pSe . ~ - - -.*• — . •••■■»•■•-• /• . % .. ‘ ' AGD/TAC:IAR/81/4 THE CONSULTATIVE GROUP ON INTERNATIONAL AGRICULTURAL RESEARCH TECHNICAL ADVISORY COMMITTEE « Twenty-fifth Meeting, Addis Ababa, Ethiopia i 24th February - 3 March, 1981 PLANT NUTRITION STUDY Working paper prepared for TAC by Pedro A. Sanchez and John J. Nicholaides, III (Agenda Item No. 7) » * TAC SECRETARIAT FOOD AND AGRICULTURE ORGANIZATION OF THE UNITED NATIONS ROME, 1981 r TABLE OF CONTENTS Page I. SUMMARY 1 II. INTRODUCTION ........................................................................... 4 A. Importance of Plant Nutrition to World Food Production 4 B. Terms of Reference .......................................................... 5 III. PLANT NUTRIENT SOURCES AND USES .’ ...................................... 9 A. Soil Reserves................. .................... 9 B. Inorganic Fertilizers ........................ 10 C. Biological Nitrogen Fixation .............. 12 D. Organic Fertilizers ........................... 13 E. Increasing the Efficiency of Input Use 13 F. Dependency on Soil Constraints . . . . 14 IV. MAJOR WORLDWIDE ASSESSMENTS 33 A. Crop Productivity: Research Imperatives (October 1975) ..... 33 B. Cornell-National Science Foundation (1976) ............................ 33 C. FAO: Improved Use of Plant Nutrients (1977) ........................ 33 D. National Academy of Science: World Food and Nutrition Study (1977).................................. .................................................. 33 E. Soil Constraints Conference (1979) ...................................... 34 F. North Carolina State University: Soil Management Planninq (1979) ...................................................................................... 34 G. Bonn Conference on Agricultural Production (1979) .... 34 V. RESEARCH AND DEVELOPMENT NEEDS 37 A. Research Components Related to Resource Appraisal .............. 37 1. Soil characterization and classification ........................ 37 2. Interpretation of soil classification into plant nutrient constraints ........................................................................ 38 3. Soil fertility evaluation ................................................ 38 4. Fertilizer supplies, price, distribution and use .... 39 5. Fertilizer manufacturing technology ............................... 40 B. Research Components for Alleviating Stress Factors .............. 40 1. Selection of germplasm ....................................................... 41 2. Management of soil acidity........................... .................... 42 3. Salinity ............................................................................... 43 C. Research Components for Alleviating Nutritional Constraints . . 44 1. Nitrogen fertilizer efficiency . 44 2. Phosphorus fertilizer management 45 3. Nutrient balance .............. ... 45 4. Sulfur . . ............................... 46 5. Micronutrients ........................... 46 Page D. Research Components for Utilizing Biological Resources .............. 47 1. Biological nitrogen fixation (BNF) ......................................... 47 2. Organic residue utilization .................................. .............. 48 3. Photosynthetic efficiency ....................................................... 49 4. Rhizosphere effects ................................................................. 49 5. Basic stress physiology and genetics ...................................... 50 E. Research Components for Alleviating Physical Soil Constraints . 50 1. Water management in rainfed farming systems 50 2. Erosion prevention and control ................. 51 3. Mechanical impedance .................................. 52 4. Land clearing methods ............................... 53 F. Research Components Related to Improving Farming Systems .... 53 1. Sustained production in Oxisols and Ultisols 53 2. Multiple cropping ......................................... 54 3. Agroforestry ................................................... 54 4. Intensive fertilization of high value crops 55 5. Management of irrigated farming systems in arid regions . . 55 6. Low chemical input farming systems .............. 56 G. Technology Transfer Needs .................................. 57 1. Validation and adaptation of research results 57 2. Training . . ................................................... 57 3. Develop effective fertilizer recommendations to farmers . . 58 4. Information services 58 H. Towards a Systematic Approach for Plant Nutrition Research ... 58 VI. SUGGESTED RESEARCH FRAMEWORK 60 A. Rationale for the Agroecologi cal Zone Approach 60 B. Assessment Parameters ...................................... 61 C. The Humid Tropics ............................................ 61 D. The Semiarid Tropics ......................................... 63 E. The Acid Savannas ............................................ 64 F. The Wetlands ....................................................... 65 G. The Steeplands ................................................... 66 H. General Considerations ...................................... 67 VII. PRESENT RESEARCH INVOLVEMENT 75 A. CGIAR System ............................... 75 B. Other International Organizations 76 C. Developed Country Institutes . . 77 D. National Research Systems . . . 78 E. General Remarks ........................ 79 VIII. APPROACHES FOR TAC/CGIAR CONSIDERATION 82 A. General Considerations ........................... 82 B. Institutional Approaches ........................ 84 C. Considerations for Evaluating Approaches 86 IX. LITERATURE CONSULTED 87 ten*-— I. SUMMARY On May 10, 1980 the authors were asked by TAC to undertake a study on plant nutrition research for consideration of TAC/CGIAR. The purpose of the study is to assess the present status and efforts on plant nutrition research as to their degree of adequacy and whether additional efforts in this field should be consid­ ered by the CGIAR system. Considering the related recent worldwide priority assessment studies which have had major inputs from developing countries, the authors have given emphasis to synthesizing the above findings in terms of re­ search needs, developing a research framework for action, and suggesting three approaches to TAC. The highlights of our findings are: 1. Food production in developing countries will be more heavily dependent on improved plant nutrition through added fertilizer inputs over the next 20 years than in the past two decades. Estimated reserves of the plant nutrients in soils, reserves of feedstock sources for producing nitrogen fertilizers and phosphorus, potassium and sulfur deposits are generally adequate to cover expected needs. Uneven distribution and development of feedstock nitrogen sources, phosphorus and potassium deposits among countries or regions, as well as rising costs, pose sign­ ificant limitations. 2. Current estimates indicate that approximately 46% of the N, P and K sup­ plied annually to the world's crops comes from the release of soil reserves, 40% from inorganic fertilizers and a small proportion from organic fertilizers, bio­ logical nitrogen fixation and atmospheric deposition. However, in order to main­ tain productivity, the soil reserves cannot be extracted continuously without being replenished. As nutrient demands are increased by intensified crop production while the amounts of nutrients released from soil reserves remain relatively con­ stant, the need for additional nutrients from other sources becomes evident. 3. The need for increasing both the amount of fertilizer use and the effi­ ciency of utilization is underscored by the fact that inorganic fertilizers have made a major contribution to food production in the developing countries. Approxi­ mately 50% of the yield increase of cereals in developing countries over the last 30 years has been attributed to the use of inorganic fertilizers. Projections in­ dicate that this proportion will increase as most of the additional crop nutritional needs worldwide will be met by inorganic fertilizers. Increasing the efficiency of fertilizer use also will involve careful attention to the use and management of organic manures, crop residues and biological nitrogen fixation. However, the increasing demand on dung and crop residues for fuel will limit their availability for soil application. 4. Plant nutrition constraints cannot be separated in practice from other soil-related constraints. The efficiency of utilization of fertilizers and amend­ ments, biological nitrogen fixation and other nutritional components is so depen­ dent on other soil constraints that it cannot be considered as a separate "factor." Examples of such constraints are soil acidity, surface soil crusting, moisture limitations and erosion hazards. Other related constraints include inadequate soil inventories, insufficient knowledge of fertilizer marketing and limited tech­ nology transfer process. Consequently, the authors found it necessary to broaden the original terms of reference to include soil-related constraints. H:- 2 5. Seven major assessment studies have been conducted during the past five years to identify priority research areas on plant nutrition-related research. Over 300 scientists and administrators from more than 50 countries provided input in identifying such priorities. Participants included members of IARC's and several of the studies had the sponsorship of various CGIAR donors. A clear con­ sensus developed with respect to the major problems, and the desirability of spe­ cific focus along agroecological zones. 6. Thirty-two research components were identified from the assessment studies. Five components relate to resource appraisal, three to overcoming soil stress factors, five to alleviating nutritional constraints, five to better utiliz­ ing biological resources, four to alleviating soil physical constraints, six to improving farming systems and four to technology transfer needs. 7. Five major agroecological zones, the humid tropics, semi arid tropics, acid savannas, wetlands and the steep!ands were identified as the regions requir- mg more attention. TJTese zones represent the regions of the developing world where soil-plant nutrition constraints are expected to exert most pressures against production increases, as well as endangering the deterioration of the land resource base. Plant nutrition aspects in irrigated farming systems were recognized as im­ portant, but better treated within the context of water management. 8. The priority research components were arranged along the five agroecolog­ ical zones according to several criteria, including research need, impact over short and long terms, relative magnitude of cost, ease of transfer, expected payoff and present capability. A suggested research framework was developed as an agro­ ecological zone x research component matrix. 9. The present status and efforts on major soil-piant nutrition research for developing countries were identified and discussed briefly. Although it was con­ cluded that, with certain exceptions, soil-plant nutrition research is not a ne­ glected area, many of these efforts are not conducted ina manner sufficiently coordinated to produce maximum benefit and interchange of information. 10. The findings were then examined in relation to TAC/CGIAR objectives, particularly the 1979 Priorities Paper. It was concluded that the present efforts and their geographical distribution are clearly insufficient to provide a reason- able degree of certainty that technology for alleviating soil-plant nutrition con- straints will be adequately developed and transferred in order to permit continuing increases of sufficient magnitude in food production. An international effort is needed in order to overcome this gap. 11. The authors recommend that TAC consider rearranging "plant nutrition" and "soil and water" into "soil-piant nutrition" and "water management" as more appropriate subjects of factor-oriented research, Plant nutrition is an important component in both areas. Soil-piant nutrition would address primarily rainfed agricultural systems where soil constraints are generally more acute than water constraints. Water management would encompass factors related to irrigated agri­ culture where the primary constraint is the management of irrigation water. 12. The authors also consider that the issue of location specificity should be brought into focus in terms of soil-plant nutrition research. The suggested research framework encompasses the kinds of problems that are generally encountered L- -*«w •• .-J-l- -- -• - - --ì-iw . 3 through one or more of the agroecological zones. The degree of expression of these problems is indeed location specific, but the kinds of problems are of international relevance. 13. The authors suggest that TAC initiate actions designed to better coor­ dinate and strengthen international research on soil-piant nutrition in order to: a) Increase the efficiency of plant nutrient inputs; b) increase and stabilize food production in marginal areas of the developing countries with emphasis on rainfed areas; c) conserve the land resource base, particularly in the priority agroecological zones. 14. Three institutional approaches are presented for TAC consideration: a) Strengthening the existing organi cations, with the suggestions that additional emphasis be given to certain soil-plant nutri­ tion research components in the current CGIAR system and that donors be encouraged to strengthen and continue other ongoing pertinent activities such as bilateral programs and particularly b) Develop a coordinating and catalytic center to foster soil-plant nutrition research, particularly in established national and international institutes. Such a center would have a small secretariat of highly qualified staff to perform the service function. c) Create a full-fledged international institute on soil-plant nutrition research with emphasis on rainfed systems. 4 ' 4 II. INTRODUCTION A. Importance of Plant Nutrition to World Food Production Plant nutrition can be defined as the portion of biology that deals with the factors affecting the supply and use of the 16 elements essential for plant growth and development (Table 1). Within the context of CGIAR objectives, the principal concerns center on the nutrition of plant species that directly or indirectly pro­ vide the basic food sources in developing countries and the constraints affecting the utilization of such nutrients. Plant nutrition, unquestionably, is one of the key factors affecting world food production and quality. The crops that feed present and future populations depend on adequate nutrition for sustained yields. Nutrients released from the soil with very few exceptions, need to be supplemental with external input in most settled food production systems. Nutrient reserves in soils are exhaustible and need to be replenished in order to maintain productivity. The different sources of plant nutrients, the interactions among them and the efficiencies with which they are utilized are major practical concerns. Much of the current emphasis focuses on the contribution of inorganic fer­ tilizers. Nearly 75% of the food production increases in the developing countries since 1950 has been due to increasing yields per hectare. The use of inorganic fertilizer has been the most important technological factor, contributing approxi­ mately 50% of these yield increases (von Peter, 1980). The aggregate use of fer­ tilizers in developing countries, unfortunately.is low. Currently, the developing countries use only 27% of the world's inorganic fertilizers to produce 28% of the world's cereal grain, yet farm 60% of the world's land planted to cereal and contain 73% of the world's population (FAO, 1980a). Table 2 shows the estimated contribution of fertilizers to cereal grain pro­ duction in three developing regions. The percent increase in production due to fertilizer use averaged 29%. Due to the limited land area where fertilizers were applied, their overall contribution to cereal crop production in developing coun­ tries during 1972-1973 averaged only 15%. The World Bank (1979) has estimated that about 50% of all food production increases in the next 20 years in developing countries will be achieved through increased fertilizer use along with other associated agricultural inputs. Through 2000, inorganic fertilizer use in the developing countries is projected to in­ crease at a faster rate than at present (IFDC/UNID0, 1978; World Bank, 1979). The latter report stated that "undoubtedly the increased use of fertilizer is the most impor­ tant way to increase crop production and help developing countries become self-sufficient in food production." However, "it is un­ likely that the overall fertilizer deficit and hence food produc­ tion will improve to a satisfactory level unless there is a major attack on the constraints which prevent fertilizer use." (World Bank, 1979). 5 As important as inorganic fertilizers are to plant nutrition and world food production, their increased use is only a partial answer. Energy limitation and the consequent cost of fertilizer production have a great deal of bearing on the inorganic fertilizer picture. For example, in the case of inorganic fertilizer N, which is the most energy-consuming and expensive to produce, not only must alternate hydrocarbon foodstocks be found, but also increased efficiencies of N fertilizer use must be developed. Additionally, closer looks at organic and biological sources of nutrients must be taken. Just as inorganic fertilizers are not the only factors limiting adequate plant nutrition, seldom is plant nutrition the only factor limiting crop produc­ tion. Crop yield and quality are a function of crop, soil, climate and manage­ ment, with each factor encompassing numerous variables. Even when plant nutrition factors are optimum, including the most judicious use of inorganic fertilizers, if any other factor, such as water, is more limiting and not alleviated, crop production will not be improved. Water stress is one of the most frequently limiting factors affecting the utilization of plant nutrients. It is not surprising, therefore, that major efforts in increasing irrigation are taking place. At present 201 million hec­ tares, 14% of the world's cropland, are under some form of irrigation (FAO, 1980a). The remaining 86% of the world's cropland depends on rainfall for its water supply. Although no statistics are available, it is safe to assert that a major propor­ tion of the fertilizers used in developing countries is used in irrigated crop­ land areas as well as plantation agriculture. Improved plant nutrition is ex­ pected to play a key role both in irrigated and rainfed farming systems during the next decades. The overall importance of plant nutrition to world food production is further emphasized in the seven recent independent major studies of the world food situa­ tion conducted with the last five years. They have all stressed the critical need for overcoming constraints related to plant nutrition for increased world food production. B. Terms of Reference Participants of the May 1979 CGIAR meeting felt that priorities for new ini­ tiatives by the CGIAR in the field of factor-oriented research, plant nutrition research, in particular, required further assessment by the TAC (CGIAR, 1980). The authors of this report were asked by TAC on 10 May, 1980 to undertake a study on plant nutrition research for consideration of TAC/CGIAR. In the subse­ quent months, several outlines for the report were proposed by TAC and by the authors and were discussed. An acceptable outline was agreed upon by the TAC Steering Committee and the authors. An interim report following part of that outline was submitted by the authors to the TAC Chairman on October 16, 1980. The study objectives were: 1. To develop a background paper which would address, at least generally and briefly, the following topics: a) The importance of plant nutrition in world food production b) The plant nutrient sources and use from -mineral and organic soil reserves -inorganic chemical fertilizers 6 -biological nitrogen fixation, both symbiotic and non-symbiotic -recycling of organic residues and wastes 2. To present, against such a background, the following: a) Plant nutrition research priorities by major recent assessments. b) Grouping of the consensus plant nutrition research priorities along specific agroecological zones within the framework of short and long-term impact, magni­ tude of cost, ease of transfer, payoff and existing capabilities of national and international research institutions. c) Detailing major current involvements in addressing these plant nutrition research priorities of various institutions in developing and developed countries. 3. To suggest, against such a background, alternatives for CGIAR/TAC consideration in addressing priority plant nutrition research needs. As one or both of the authors of this report were fortunate to have partici­ pated in the last four studies concerning plant nutrition research needs and have traveled extensively to developing and developed countries during their leadership of one of these studies, it was felt by the TAC Steering Committee and the authors that major additional travel in the development of this report would be unnecessary. A three-day visit was made to IFDC in November 1980 to augment information the authors had gathered in the course of the other studies and the present one. The TAC Priorities Paper (TAC, 1979a) and the Report of the TAC Mission to IFDC (TAC, 1979b) proved especially useful as background materials for the pre­ paration of both the interim and final draft reports. Many other reports, arti­ cles, books and personal communications concerning plant nutrition and the world food problem were utilized in the course of this study. From these, the pertinent information has been distilled, summarized and used in the present report. Gratitude is expressed to Drs. R. W. Cummings and J. K. Coulter, who comprised the TAC Steering Comnittee for this report, and to M. P. Mahler for their valuable advice and suggestions in the preparation of this report. Acknowledgement and thanks are extended to Drs. D. L. McCune, P. J. Stangel (IFDC), R. Dudal (FAO) and several NCSU faculty for supplying requested materials which otherwise would have been unavailable or extremely difficult to obtain. 7 Table 1. Nutrient elements essential for plant growth and development and their sources. Essential elements used in Essential elements used in relatively large quantities relatively small quantities Mostly from Primarily Primarily air and water from soil solids from soil solids Carbon Macroelements : Microelements: Hydrogen Primary elements: Boron Oxygen Nitrogen** Chi orine Phosphorus Potassium Copper Iron Secondary elements: Manganese Calcium Magnesium Molybdenum Sulfur Zi nc *Source: Brady (1974). **Biological nitrogen fixation and atmosphere also contribute nitrogen to plants. 8 Table 2. Estimated contribution of fertilizer to cereal grain production in developing market economies, 1948-1952 to 1972-1973.* Increase in Estimated Percent Estimated total annual increase increase total production cereal due to due to due to fertilizers Region production fertilizers ferti1izers (1972-1973) million tons % % Asia 81.5 26.2 32 15 Latin America 40.5 10.8 27 16 Africa 12.4 2.5 20 6 Total 134.4 39.5 29 15 ♦Calculated from IFDC/UNIDO (1978). 9 III. PLANT NUTRIENT SOURCES AND USE Though the contribution of other essential nutrients to crop production is acknowledged, this section shall focus mainly on the primary nutrients due to their overriding importance for crop production. Due to the lack of complete information in the literature regarding the ab­ solute and relative contributions of major sources of primary nutrients to the world's crops, the authors have calculated gross estimates of primary nutrients supplied annually to the world's 1414 million hectares of cultivated and permanent crops (Table 3). The major sources of primary nutrients were considered to be those released in available form from soils, inorganic fertilizers, organic fer­ tilizers, biological nitrogen fixation and atmospheric deposition. Available primary nutrients released from the soil and from inorganic fertilizers com­ prised most of those supplied to the world's cultivated and permanent crops, with soil release providing 46% and inorganic fertilizers 40%. Cereals, legumes and roots-crops occupied 68% of the world's cultivated and permanent cropland in 1979. Total uptake of primary nutrients by these crops is estimated in Table 4. By calculating 68% of the total N, P2O5, K20 supplied to the 1414 million hectares, a very rough estimate of the nutrient uptake by cereals, legumes and roots-crops was obtained, Those are, in million tons, 86 N, 37 P2O5, and 68 K20 for a total of 191. Thus, estimates of the overall efficiencies of nutrient uptake by these crops to nutrients supplied from al 1 sources indicate 73% (63/86) for N, 62% (23/37) for P205 and 87% (59/68) forT20. A. Soil Reserves Although large total amounts of reserves of essential elements are contained in the soil (Table 5), the capacity of the soil to supply these in available form to plants is limited. It should be recognized that even the small amounts of total nutrient reserves released annually in available form to plants cannot con­ tinue to be released, or "mined" without being replenished—from whatever source. Most soil N reserves are in organic form and small portions are mineralized slowly to become plant available. Most soil P reserves in the mineral fraction are in­ soluble forms of iron, aluminum, occluded and calcium phosphates and only slowly over time do small portions of some of these become available to plants, Some P is present in organic matter, but that mineralized is commonly incorporated into the solid inorganic fraction. Potassium availability in contrast, is generally governed by weathering of primary minerals. Published data with accurate estimates of the amounts of essential elements supplied to crops solely from nutrient reserves are difficult to find, Based on calculations using primary nutrient uptake data by non-fertilized cereals, the authors were able to arrive at the following gross estimates of primary nutrients released annually to crops from mineral and organic soil reserves: 30 N, 15 P205 and 47 K20 in kg/ha (Table 3). However, the situation is certainly variable, e.g • 5 K20 supplied to crops from Ultisols and Oxisols is estimated to be substan­ tially less. Overall, the amount of available primary nutrients supplied from reserves in the soil totals 92 kg/ha, while that estimated to have been applied from inorganic sources in the developing countries in 1980 was 32 kg/ha (Table 6). 10 B. Inorganic Fertilizers Our estimates are that inorganic fertilizers comprise 40% of the primary nutrients supplied to crops worldwide (Table 3). World Bank (1979) estimated that inorganic sources furnish "the majority of crop nutritional needs worldwide." The bulk of crop nutritional needs on a world scale through at least 2000 are projected by World Bank (1979) to continue to be from inorganic sources, which, in addition to the primary nutrients, includes Ca, Mg, S and the micronutrients. The World Bank report indicated that in terms of cost for the individual farmer and foreign exchange for the developing nations, inorganic fertilizers will be the most important input in crop production from present through at least 2000. Indeed, FA0 (1980c) reported that the developing countries' share of the imported fertilizers increased from 6% in 1972/73 to 32% in 1978/79. The developing countries' share of raw materials required in the annual production of inorganic fertilizers are expected to increase from about 28% to almost 40% between 1980 and 2000 (Table 7). 1. Nitrogen. Industrially-produced N fertilizer is critical for the pro­ duction of cereal grain, which is the world's major food source. Our estimates are that inorganic fertilizers furnish 44% of the annual N supplied to the world's cultivated and permanent cropland (Table 3). World demand for N fertilizer is projected to increase from 56 million tons in 1980 to 140 million tons in 2000, with developing countries' demand increasing from 33 to 39% of the total (Table 8). World N supplies from 1980 through 2000 are expected to exceed demand by several percentage points each year, with the developing Countries' production programs approaching the suggestion by an UNIDO study of group self-sufficiency in N and P fertilizers by 2000 (IFDC/UNID0, 1978). Thus, by 2000, about 40% of the world's N production capacity may be located in developing countries. Natural gas will continue to be the main feedstock for armonia plants to pro­ duce N fertilizer, though its use is projected to decrease from 72% of the plants built from 1980 to 1985 to 64% in 1990-2000. Coal will increase from 9% to 17% in these same years, with naptha and oil comprising the other 5 and 15%, respec­ tively (IFDC/UNID0, 1978). The developing countries most likely will use natural gas as a feedstock for ammonia production (Stangel, 1977). Nearly 80% of the N fertilizer will be urea or ammonium nitrate, with 10% each coming from anhydrous ammonia or ammonium sulfate and the N content of ammonium phosphates (IFDC/UNID0, The 1977 reserves and production of natural gas, petroleum and black coal in developing and developed regions of the world are presented in Table 9. The world's 1977 known reserves of petroleum and natural gas by country are shown in Table TO. From these tables, it can be concluded that ammonia feedstocks are widely distrib­ uted among both developed and developing countries, that developing countries' reserves are much greater relative to their current production rates than are those of developed countries, and that coal supplies are more than adequate for ammonia production. However, although these hydrocarbon feedstocks are available in adequate quantities, they are likely to become increasingly more expensive. 2. Phosphorus. Our estimates are that inorganic fertilizers furnish 54% of the P205 supplied annually to the world's cultivated and permanent cropland (Table 3). World demand for P205 is anticipated to grow from 30 million tons in 11 1980 to 64 million tons in 2000, as developing countries' demand of the total increases from 25 to nearly 37% (Table 8). World production of phosphate rock by country and region are presented in Tables 11 and 12, respectively. Ample known reserves of phosphate rock exist (Table 13); in fact, rate of discovery exceeds rate of consumption (IFDC, 1978). Quality of reserves is variable, but supplies are expected to exceed demand by several percentage points per year as the developing countries attempt to become self-sufficient in phosphate. Concentrated fertilizers shall continue to be the trend with diammonium phos­ phate (DAP), monoammonium phosphate (MPA), and triple superphosphate (TSP), comprising, respectively, 50, 30 and 20% of the total (IFDC/UNID0, 1978). The direct application of ground or partially acidulated phosphate rock (current use estimated at 8% worldwide) could decrease the need for chemically manufac­ tured phosphates. Phosphate fertilizers will be used more in compound fertili­ zers, comprising 65% and 86% of the P205 consumed in developing and developed countries, respectively, by 2000 (IFDC/UNID0, 1978). 3. Potassium. Our estimates are that inorganic fertilizers furnish 27% of the K20 supplied annually to the world's cultivated and permanent cropland (Table 3). World demand for K20 will increase from 27 million tons in 1980 to 60 million tons in 2000, with developing countries' share of world demand increasing from 16 to 24% of the total (Table 8). Though ample reserves of potash exist (Table 14), most lie in a few developed countries; thus, most developing countries will have to rely on K20 imports for the-foreseeable future, although some new potash deposits have been found in Brazil, Ethiopia, Iran, Laos, Libya, Morocco, Pakistan, Peru, Poland, Thailand and Tunisia. Deposits are being mined in China and Chile, while Brazil, Jordan and Poland have exploitation plans (IFDC/UNID0, 1978). Potash sup­ plies should equal or slightly exceed demand in the future. However, 50-60% of the new planned potash capacity is in the USSR and, if delayed, could precipitate a tight potash supply (World Bank, 1979). 4. N:P:K ratios. Through 2000 the developing countries are expected to main­ tain a nutrient ratio of 4:2:1 for N:P205:K 0, while the developed countries are expected to increase the N of the 1974 ratio of 1.4:1:1 to 2.2:1:1.1 by 2000 (IFDC/UNID0, 1978). Thus, from 1980 through 2000, the greater part of fertilizer growth will be in N, increasing 151% from 56 to 140 million tons. The growth of P205 and K20 will increase 113% from 30 to 64 million tons and 122% from 27 to 60 million tons, respectively. The demand of the developing countries by 2000 is projected to be for nearly two-fifths of the N, more than one-third of the P205 and about one-quarter of the K20. 5. Sulfur. Sulfur supplies are expected to be more than adequate to meet fertilizer needs through 2000 and beyond (Stangel, 1977). This is due to the in­ creasing emphasis on pollution control which will necessitate large amounts of S being recovered and disposed. This recovered S exceeds S demands by the phosphate industry and if economically feasible will be so used. Due to the higher analysis fertilizers being used, S deficiencies are being noted more and more on a global scale (Blair et al., 1980). World production of sulfur by country in 1975 is pre­ sented in Table 71>. Annual consumption of S for fertilizer production is projected to increase from 25 million tons to 65 million tons from 1980 to 2000, with a total consumption during these years of about 900 million tons or less than 20% of the reserves (Table 16) at present being used (IFDC/UNID0, 1978). 6. Lime. Lime supplies, both calcitic and dolomitic, are expected to exceed demand through 2000, though use is not equivalent to what is required at present. Even in the United States, lime use has been essentially static at around 25 12 million tons per year since 1947 (Nicholaides, 1981). In the developing countries, lime use also is much less than that required, With increased research in eval- uation and development of crop species and varieties tolerant to soil acidity and the consequent use of these varieties in developing countries, lime supplies in developing countries are expected to be sufficient well beyond the 21st century. 7. Micronutrients. Micronutrient supplies and demand are more site-specific, hence, information is limited. However, the generalizations can be made for B, Cl, Cu, Fe, Mn, Mo and Zn that supplies are adequate to meet demand beyond 2000. As the macroelements become less limiting to crop yields through increased and judicious use, the microelements are expected to take on increased importance in crop production. C. Biological Nitrogen Fixation Although biological sources undoubtedly contribute to nutrients supplied to the world's crops, the only one for which there is a reasonable estimate of its contribution is biological nitrogen fixation (BNF) through the syrrtbiotic Rhizobia- legume relationship. 1. Rhizobia. Biological nitrogen fixation via Rhizobia are estimated to supply 12.7 million tons annually to world crops (Frissel, 1978), about 10% of the total annual N supply (Table 3). Hardy and Havelka (1975) speculatively esti­ mated that Rhizobium-legume symbiosis contributes 80 million tons of N annually to agricultural soils, being split approximately equally between crops and pastures. Other estimates (NAS, 1977b) are for 35 million tons of N being fixed by agricul­ tural legume crops. The authors of this report feel that the data quoted by Frissel are more believable, especially when crop legume N uptake, yields and hec- tarage are considered. Legume (soybeans, peanuts, pulses) uptake of N was cal­ culated to be 88 kg/ton yield (Table 4). In 1979, 165.3 million tons of legume grain were produced on 148 million hectares (FA0, 1980a). Multiplying 88 kg N/ton legume yield by 165.3 million tons, one obtains the figure of 14.5 million tons of N taken up by grain legumes in 1979. This is closer to Frissel's 12.7 million tons than the other reported estimates. The world's 3150 million hectares of pas­ tures are also benefited by symbiotic N fixation; the only estimate of quantities of N rhizobially fixed with pastures is the 40 million tons of N speculated by Hardy and Havelka (1975). .2. Azolja culture, blue-green algae and green manuring. The Anabaena-Azolla symbiosis offers a source of organic N fertilization or green manure under flooded conditions, and thus is of particular interest to paddy rice cultivation and of some potential magnitude in the world's cereal grain-N situation. Projections by FA0 (1978) are that Azol1 a cultivation in the developing world could produce 1.5 million tons N per year for rice. Much research with Azolla is inconclusive, although indications are that it can fix as much as 800 kg N/ha/yr (Gunasena et aj_.,1979). The Chinese have reported paddy rice yield increases with Azolla- ranging from 0.4-158%, with an average of 19% over 422 field experiments (Lumpkin and Plucknett, 1980). Blue-green algae and green manures other than Azolla are also possibilities. Some work, though inconclusive, by Dobereiner with N-fixing Spirillum lipoferumand roots of tropical grasses and maize could pose possibi1i- ties (Marx, 1977). 13 D. Organic Fertilizers Approximately 6% of the primary nutrients supplied to the world's 1414 million hectares of cultivated and permanent crops are estimated to come from organic nures (Table 3), although no data are available from crop residues remaining on harvested cropland. FAO (1975) estimated that nearly 10% of all applied fertil- c°mP°*ed ?! or9anic wastes and that there is potential to increase L-Jab0Utn25?' The total amounts of fertilizer N, P205,K20 in organic wastes 97 WaS e^im?ted the Wo^d Bank (1979) to have been^S, 16, and lion tons, respectively with cattle manure accounting for 1/3 of each nu- Thls,?otal amount of 103 million tons of nutrients in organic waste was qanijyfl?tilizprrr?ffefi t???-the+tot?1 .consumption of these nutrients from inor- gamc fertilizers (28.6 million tons) in the developing countries in 1978/79. nutrW^w6 estl"iat^ in Table 3 show that only 17 million tons of these primary trients were actually applied to the world's arable and permanent cropland. tili7prina a?n^dl^-are/5e tw0 main countnes utilizing organic wastes as fer- iV] .interesting data were presented by Kemmler (1979) showing that the . g grain production/kg N, P205, K20 aoplied in China by a combination of S9Nnlp o"d ITS"1' frt1!l“rs/s a,m0si as h,'9h as in JapanTere tSe levels N, P205, K20 consumption/ha and of cereal yields are nearly three times higher. w, . Thus, there may be possibilities for increasing the recycling of orqanic for^fnplS WcT Cr°??' however, many factors such as the competitive uses fil/hpnlrì?ss during.collect!on, storage and use and economics lessen the poten­ tial benefit of organic nutritional sources for food production small increases in the proportion of nutrients recycled could Still, even ciable food production increases (NAS, 1977c). result in appre- E- Increasing the Efficiency of Input Use The supply-demand pictures show a major urgency in increasing the total fer- 1aProduction capacity in the developing countries at an unprecedented scale sourrP, a\S0V f°rt! addnional Plant nutrients from biolSgicfl andorganic sources. That statement, however, must be brought into the context of limited energy supplies for production and distribution of nutrient inputs. fo ^ Pimentel (1979) stated that the world's energy resources are too limited to product^n0s^st^SeninPfacJatJ?n U!ilj21‘n9 the hi9h1^ enerW consuming U. S. food Deduction lf petroleum were the only source of energy for food production and if all petroleum reserves were used via the U. S hioh enorav rnn- of^fuplS!Ltem t0 pr°djjce tood for the world's population, the 87 trillion liters fpp[ hie !c^Ve? W°Uld aSt only 13 years (Pl'mentel, 1979). Though the authors 5?L5ls estimates are questionable, Pimentel makes a point. That point is fer- ikp nf^■P^educti°n systems utilizing either less energy or making more efficient use of inputs must be developed, and especially for the dev^oping^ountries. There are several ways to approach the solution and these are not mutual!v exclusive. One is certainly that major efforts are needed to produce oTant trients more efficiently. The classic western style Sels of laroe fer??lizpr -cii‘?£tdi??sJtP].0s,t,enfo,ti? «xcsoouunrctreise so' f nutrient supply and 14 the centers of food production, thereby reducing energy costs in terms of both production and transportation. Another would be looking at traditional and non-traditional agronomic ap­ proaches in developing country situations. Improved methods of placement and time of application of fertilizer nutrients will certainly play a large role in increased efficiencies of these nutrients, be they from inorganic or organic sources. The increased N efficiencies in rice production in Asia by deep place­ ment of urea supergranules is one such example (Yamada et aK, 1979). Another way of utilizing plant nutrients more efficiently would be the use of germplasm tolerant to suboptimal soil conditions. Evaluation and selection of crop species and varieties tolerant to suboptimal soil and climatic conditions, especially Al and drought tolerances, has been widely acknowledged as a major re­ search area (NAS, 1977b; NCSU, 1979; IRRI, 1980). Evaluation and selection of crops and varieties tolerant to acid soils could be of major benefit in opening up many areas of the humid tropics and seasonal savannas where these soils pre­ dominate. Evaluation and selection of salt tolerant plants could do the same for saline soils in the arid and semiarid regions of the world (FAO, 1980b). Re- search possibilities of tolerance to adverse soil conditions are not limited just to plant germplasm, as tolerances among Rhizobial strains are also varied (Add et al., 1980). Therefore, the "green revolution" must become the "adaptive revolution" in which soil scientists, plant breeders and microbiologists work together to evaluate, select and develop crop cultivars and beneficial soil mi­ crobes which are capable of producing food on less than optimal soil conditions, some of which require lower energy inputs than those produced by the "green revolution." Another possibility is improved utilization of mycorrhizae, expediters of nutrient absorption,particularly P, by plant roots. Ectotrophic mycorrhizae have long been known to be important to trees. Endotrophic mycorrhizae recently have been found to be lamost ubiquitous and to infect crops (NAS, 1977b). Mycorrhizae help supply the most infected plants with enlarged root systems, thereby improving the absorption of P, Mg, Ca, some trace elements, and water, and in legumes stim­ ulating N fixation, and improving overall growth of both non-legumes and legumes due to better mineral nutrition. Their activities are especially beneficial to tropical legumes and thus could be of importance in establishing legumes on acid soils (NAS, 1977b). Safir (1980) has summarized field work which has shown corn and wheat yield improvement with use of heavily mycorrhizal seedlings and soybean yield increases following inoculation with mycorrhizae. Thus, increasing the efficiencies of input use as related to plant nutrition can be addressed in many potential ways. Ignoring the production of plant nutrients and looking at the overall situation, one is impressed by the fact that increased efficiency of plant nutrients depends to a large extent on soil constraints. F. Dependency on Soil Constraints Plant nutrition under field conditions is far from a simple matter of supply­ ing nutrient inputs and producing crop output. In addition to the many interactions that take place among nutrient sources, several other factors exert major influence on plant nutrient efficiency. Adverse soil conditions such as high acidity, salinity or drought can easily decrease plant nutrient utilization to very low levels. Physical soil constraints such as erosion, surface crusting and others 15 can have a similar impact. It is difficult, therefore, to view plant nutrition research solely in the context of soil fertility, i.e • » the capacity of the soil to provide nutrients for optimum plant growth, One immediately asks, which soil? Which farming systems? It seems more practical to consider the broader issue in terms of soil management, i.e., the manipulation of soil properties and inputs to increase production on an agronomically, economically and ecologically- sound basis. Scientists and administrators of research programs in developing countries are increasingly aware of the importance of soil-related constraints as the next major bottleneck in tropical agricultural research. Earlier production break­ throughs came with high yielding varieties on fertile soils with adequate irriga­ tion systems. The limits of direct adaptability of such technology are largely being reached. The genetic breakthroughs and accompanying cultural practices are insufficient in the face of environmental constraints of which soil and water are the main ones. Consequently, the authors of this report decided to consider, within the scope of this study, the soil constraints that affect plant nutrition under field conditions in developing countries. Table 3. Gross estimates of primary nutrients supplied annually to the world's 1414 million hectares of cultivated and permanent crops.* N P2O5 k2o kg/ha Source % of kg/ha % of kg/ha Primary nutrients /yr Total Total /yr Total Total % of kg/ha Tof/yr Total Total /yr Total Total million t million t million t million t Soil release 30 42 34 15 21 38 47 66 66 92 86 46 Inorganic fertilizers 39 56 44 21 30 54 19 27 27 79 113 40 Organic fertilizers 4 6 5 3 4 8 5 7 7 12 17 6 Biological N fixation 9 13 10 0 0 0 0 0 0 9 13 5 Atmospheric deposition (wet and dry) 6 9 7 0 0 0 0 0 0 6 9 3 cn Totals 88 126 100 39 55 100 71 100 100 198 281 100 *?S7^re-eaSe d?ta/re.from authors' calculations based on uptake data by non-fertilized crops (Sanchez Jh,n]S^S",C,^or11frJdat! ^ f™. I™/UNID0 (1978); organic fertilizer data are ™om datS for’ j 979 ^ ai?d adJusted by dividing China hectarage by world hectarage (these organic manures do not include crop residues which have remained on harvested fields); biological nitrogen fixation and atmospheric deposition data are from Frissel (1978) 9 lxauon ana Table 4. Estimates of average uptake per ton dry matter yield of cereals, legumes and roots and tubers and total uptake of primary nutrients in 1979 on a world basis.* Crop (x yield, t/ha; N Po2O 5 K20 Primary nutrients million ha) kg/t yieldmillion t kg/t yield million t kg/t yield million t kg/t yiel d million t Cereals (2.04; 761) 27 42 11 17 28 43 66 102 Legumes** (1.12; 148) 88 15 21 4 64 11 173 30 Roots and tubers (11.0; 50) 11 6 3 2 9 5 23 13 Total 126 63 35 23 101 59 262 145 *Data calculated from that presented in Sanchez (1976), Mengel and Kirkby (1978) and FAO (1980). "-j **Soybeans, peanuts and pulses. . . - ....... • - 18 Table 5. Average contents of total reserves, the bulk of which are not di­ rectly available to plants,of selected essential nutrients in soils.* Nutrient Content kg/ha N 3,136 P2„0 5 3,055 K2„0 22,400 Ca 30,688 Mg 11,200 S 1,568 B 22 Cl 224 Cu 67 Fe 85,120 Mn 1,344 Mo 4 Zn 112 *Data adapted from Lindsay (1979). ;S'f*- ».• i» Sfili i ■ i —■ • 19 Table 6. Actual and projected fertilizer use in developing and developed countries, 1974-2000.* kg/capita kq/hectare 1974 T980TO) 2000 vm TO) 1990 20UO Developed countries 58 73 100 130 109 149 225 322 Developing countries 7 9 14 19 22 32 55 83 ♦Adapted from IFDC/UNID0 (1978). s 20 Table 7. Annual raw material requirements for fertilizer production, 1980-2000.* Developed countries Developing countries 1980 1990 2000 1980 1990 2000 Natural gas (billion m 3 ) 33.0 60.0 94.5 14.1 36.5 61.3 Naptha (million t) 5.9 7.3 8.6 2.4 3.7 4.7 Fuel oil (million t) 3.0 7.1 12.5 1.3 4.8 8.8 Coal (million t) 6.5 25.0 57.6 2.8 18.3 40.3 Phosphate rock (million t P2O5) 29.3 40.6 54.2 10.0 20.4 33.7 Sulfur (million t) 19.2 27.8 38.3 6.5 14.6 24.9 Potash (million t K^O) 24.6 36.7 51.2 4.5 8.9 14.8 * Adapted from IFDC/UNID0 (1978). -■» 21 Table 8. Estimated and projected fertilizer production and consumption or demand by developed and developing countries, 1960-2000.* _________ Production _____ Consumption/Demand World Developed** Developing*** World Developed Developing 1960: million t N 10.36 9.43 0.93 9.75 7.80 1.95 P2O5 9.96 9.24 0.72 9.84 8.90 0.94 K20 8.73 8.61 0.12 8.25 7.83 0.42 Total 29.07 27.30 1.77 27.81 24.50 3.31 1970: N 30.17 26.10 4.07 28.70 21.00 7.70 P2O5 19.32 17.0 2.32 18.85 15.60 3.25 K2Q 16.69 16.10 0.59 15.47 14.00 1.47 Total 56.18 59.20 6.98 62.90 50.50 12.40 1980: N 55.6 37.5 18.1 P2°5 30.4 22.8 7.6 K20 27.1 22.8 4.3 Total 113.1 83.1 30.0 1990: N 92.8 58.9 33.9 P2O5 45.4 31.0 14.4 K20 41.9 33.3 8.6 Total 180.1 123.2 56.9 2000: N 139.6 85.1 54.5 P2O5 63.9 40.6 23.3 K20 60.2 45.8 14.4 Total 263.7 171.5 92.2 * Adapted from IFDC/UNID0 (1978). ** Developed countries include North America, West Europe, East Europe, USSR, Japan, Israel, South Africa, Australia and New Zealand. *★* Developing countries include Latin America, Asia (except Japan and Israel), Africa (except South Africa) and Oceania (except Australia and New Zealand. Table 9. Reserves and production of natural regions of the world.* gas, petroleum and black coal in developed and developing r Natural gas Petroleum Black Coal Reserves Reserves '76 Production Reserves 76 Production Iden. Prob. 76 Production ■3 billion m -- — million t billion t- --million t — World 65,875 1,429 87,938 2,949 1,080 8,150 2,210 Developed countries 38,893 1,238 19,773 1,176 740 7,000 1,630 Dev'ed Market Econs. (N.Am • J W.Eur, Oceania, Other) 11,987 833 8,720 558 535 2,948 973 Centr. Planned Econs. (E. Eur + USSR) 26,906 405 11,053 618 205 4,052 657 rroo Developing countries 25,982 191 68,165 1,773 340 1,150 580 Africa 5,923 46 Asia and Far East 8,299 291 6 15 52,250- 28 Latin America 2,434 116 23 862,558 9558 Near East 4,604 228 9 3614,543 12 China 59 50,088 1,138 1 2708 62,740 300 1,011 458 * Adapted from IFDC/UNID0 (1978). Reserves as of January 1, 1977, except for black coal which is as of 1974. 23 Table 10. World reserves of petroleum and natural gas by country, 1977.* Oil Reserves Gas Reserves Country Jan. 1, 1977 Jan. 1, 1977 million t billion m 3 WEST ASIA Abu Dhabi 3,973 566 Bahrai n 40 85 Dubai 205 42 Iran 8,631 9,348 Iraq 4,658 764 Israel 1 Kuwait 9,234 898 Neutral Zone 863 142 Oman 795 57 Qatar 781 779 Saudi Arabia 20,550 1,785 Sharjah 4 28 Syria 301 34 Turkey 53 15 Total 50,088 14,544 EAST ASIA-PACIFIC Afghanistan 12 78 Australia 189 915 Bangladesh 227 Brunei 223 238 Burma 9 4 Taiwan 2 23 I ndi a 411 99 Indonesia 1,438 680 Japan 4 59 Malaysia 333 425 New Zealand 26 175 Pakistan 10 448 Thailand 28 Total 2,657 3,399 AFRICA Algeria 932 3,564 Angola-Cabinda 166 42 Congo Republic 39 1 Egypt 267 79 Gabon 291 71 Libya 3,494 731 Morocco 1 Nigeria 2,672 1,246 Tunisia 370 187 Zai re 68 1 Total 3,360 4,019 ~ ‘ Vv. 24 Table 10. (Continued). Oil Reserves Gas Reserves Jan. 1, 1977 Jan. 1, 1977 million t billion m 3 EUROPE Austria 22 20 Denmark 41 19 France 7 142 Germany (West) 45 212 Greece 5 227 Italy-Sicily 43 187 Netherlands 12 1,754 Norway 775 524 Spai n 60 14 United Kingdom 2,302 850 Yugoslavia 48 42 Other (Ireland) 28 Total 3,360 4,019 WESTERN HEMISPHERE Argentina 315 193 Barbados 8 Bolivia 33 142 Brazil 110 25 Canada 849 1,586 Chile 25 56 Colombia 113 142 Ecuador 233 340 Guatemala 3 Mexico 1,507 340 Peru 102 62 Trinidad and Tobago 71 97 Venezuela 2,092 1,153 United States 4,288 6,232 Total 9,741 10,376 CENTRALLY PLANNED ECONOMIES Bulgaria 2 2 Chi na 2,740 708 Czechoslovakia 3 19 Hungary 43 121 Poland 11 124 Romania 294 640 U.S.S.R. 10,700 26,000 Total 13,793 27,614 TOTAL WORLD 87,938 65,881 ♦Source: IFDC/UNIDO (1978). UMhéùlU* -.*• w — 25 Table 11. World production of phosphate rock by country, 1976.* Portion Country Product of Total 1000 t United States 44,671 41.8 U.S.S.R. 24,200 22.6 Morocco 15,293 14.3 Chi na 3,400 3.2 Tunisia 3,294 3.1 Togo 2,067 1.9 Senegai 1,796 1.7 Jordan 1.717 1.6 South Africa 1,639 1.5 Vietnam 1,500 1.4 Christmas Island 1,033 1.0 Israel 831 Algeria 820 Nauru Island 755 Syrian Arab Republic 511 India 510 Brazil 463 Korea, Democratic Republic 450 Egypt 443 Ocean Island 417 > 5.9 Australia 248 Mexico 197 Sahara 173 Rhodesia 130 Germany, Federal Republic 85 Venezuela 80 Curagao 54 Sweden 25 Uganda 15 Peru 2 Colombia 1 y Total 106,820 100.0 *Source: IFDC/UNID0 (1978). r- 26 Table 12. World production of phosphate rock by regions, 1976.* Phosphate rock — 1000 t — World 106,819 Developed Regions 71,434 North America 44,671 West Europe 110 East Europe 24,200 Oceania 2,453 Developing Regions 35,385 Afri ca 25,227 Asia and Far East 510 Latin America 797 Near East 3,501 Socialist Asia 5,350 ♦Source: IFDC/UNIDO (1978). ~ • ■. ; -i -- • K '»TJ'tfìW •. • 27 Table 13. World phosphate reserves and resources, 1977.* Total reserves av^e2^ ra5ge Country and resources or range Remarks million t - — % — AFRICAa Al geria 1,000 Angola 120 Egypt 2,800 Liberia 1.5 Al-Fe phosphate Mali 20 Mauritania 5 Exploration incomplete Morocco 40,000 West Sahara 16,600 Senegal Taiba 1,100 Thies 2,090 Aluminum phosphate Tanzania 10 Togo 300 Tunisia 1,300 Rhodesia 20 South Africa Palabora 1,400 Other 35 Uganda 200 Upper Volta 4 May be much larger Zai re 83 Total 67,189 WEST ASIA Iran 130 Iraq 660 Israel 1,000 Jordan 1,000 Ore of all grades above 15% in drilled area Lebanon small Saudi Arabia 1,000 Syria 800 Turkey 300 Total 4,890 EAST ASIAC Chi na 30,000 Christmas Island 200 29-38 Includes aluminum phosphate I ndi a 140 17.5 Assumes 100 at Jhamar Kotra Korea, North 88 12.5 Mongolia 1,000 20-22 Pakistan 12 20-37 Paracel Islands 20 10-27 Ownership disputed Sri Lanka 300 30 Vietnam 500 30 b Total 17,260 (China adjusted to 15,000 million tons of equivalent 30% ^5) 28 Table 13 (continued). P«0 Total reserves av^r^ge Country and resources or range Remarks - million t - —.% — OCEANIA Australia 2,000 30b Nauru 44 38.5 Ocean Island 2 40 New Zealand 70 30 Underseas nodules Total 2,116 NORTH AMERICA Canada 50 9 Igneous deposits U.S.A. Eastern 19,900 26 Western 14,700 26 Alaska 1,000 25 May be larger Mexico 1,000 30 b May be larger; does not include b underwater140 30 Total 36,790 SOUTH AND CENTRAL AMERICA0 Aruba 10 30 b Aluminum phosphate Brazil Bambui 700 30b Olinda 20 30b Igneous 1,000 30b Carbonati tes Other 25 b Aluminum phosphate Colombia 600 ?305b Chile 4 New discovery, may be much larger Curacao 10 ?2b Peru 6,100 ??b Venezuela 40 3?02b Total 8,509 EUROPE including U.S.S.R. Finland Sakli 200 18 Siilinjarva 25 10 Ireland 8 25 Norway 100 6-10 Igneous Sweden no estimate Igneous U.S.S.R. Kola 1,125 39.4 Estimated recoverable concentrate Other 6,000 14 Various sedimentary deposits. Some Total 7,458 new discoveries may not be included. WORLD TOTAL 144,212 29 Table 13 (continued). a. Other countries that have small or unquantified deposits incude Cameroon, Benin, Gambia, Niger, Gabon, Nigeria, Dahomey, and perhaps Chad. b. Tonnage and grade stated in terms of equivalent quantity of marketable phosphate rock of 30% P^Oc grade or higher. c. Also small or unquantifrea deposits in Cambodia, Malaysia, Taiwan, Japan, Philippines, and Indonesia. d. Also small amounts on various islands. e. Also small or unquantified deposits in Belgium, Bulgaria, France, Germany, Greece, and Yugoslavia. ♦Source: TFDC/UNIDO (1978). ■ .'.jfri',,, C,;,.- ----- - ■«.> • »w»—. 30 Table 14. World potash production and reserves by country, 1975-76.* k2o k2o Country production reserves -1000 t - million t U.S.S.R. 7,944 15,900-24,000 Canada 4,842 18,000-66,500b Germany, Democratic Republic 3,019 4,000-10,000 Germany, Federal Republic 1,950 2,000-9,000 United States 2,220 200-400° France 1,720 200-270 Israel 716 500-2,000d Spain 506 80-270 Chi na 450 no estimate Congo 278 17-70 Italy 141 200 United Kingdom 34 20 Chile 10 no estimate Others 5 no estimate Total 23,835 35,517-112,730e a. Source of production data: British Sulphur Corp., Statistical Supple­ ment No. 14, November/December 1976. b. Does not include deposits in New Brunswick. c. Does not include deposits in North Dakota and Montana. d. Dead Sea, including Jordan. e. Other deposits not being mined and with no reliable estimate of reserves in Brazil, Ethiopia, Iran, Laos Libya, Morocco, Pakistan, Peru, Poland, Thailand, and Tunisia. *Source: IFDC/UNID0 (1978). --- ----- - 31 Table 15. World production of sulfur (all forms) by country, 1975.* Country Production — 1000 t — % of total United States 11,800 22.8 U.S.S.R. 9,460 18.2 Canada 7,420 14.3 Poland 5,040 9.7 Japan 2,400 4.6 Mexico 2,200 4.2 France 1,940 3.7 Spai n 1,560 3.0 Germany, Federal Republic 1,070 2.1 Italy 710 1.4 Iraq 600 1.2 Fi nland 510 1.0 Iran 475 0.9 Germany, Democratic Republic 365 0.7 South Africa 355 0.7 Sweden 266 0.5 Norway 262 0.5 Australia 255 0.5 Others 5,157 10.0 Total 51,845 100.0 * Source: IFDC/UNID0 (1978). ,̂.l. ______ 32 Table 16. World sulfur reserves and production, 1974.* Sulfur reserves Sulfur Identified Probable Total production million t Elemental : Evaporites 580 100 680 17.6 Volcanic rocks 130 100 230 Natural gas 155 885 1,040 Petroleum 265 1,330 1,595 15.0 Pyri tes 640 >640 11.0 Metallic sulfides 260 >140 >400 8.2 Subtotal 2,030 >2,555 >4,585 51.8 Tar sands 50 >1,800 >1,850 Coal 20,000 200,000 220,000 Oil shale 280,000 Gypsum Vast Total 22,000 >200,000 >500,000 Source: IFDC/UNID0 (1978). 33 IV. MAJOR WORLDWIDE ASSESSMENTS The increasing awareness of the importance of plant nutrition on world food production has stimulated a series of studies on research priorities related to plant nutrition. Seven major studies were conducted during the last five years, where working scientists met and developed a list of priorities in response to requests from different sponsoring institutions. Many other conferences have dealt with this subject during the last five years but the authors of this study are not aware of other studies that led to detailed research, priorities formulated by scientists actively engaged in plant nutrition research for the developing world. A short description of the seven studies follows in chronological order. Table 17 summarizes the outcome of these studies under a common format. The term "research component" is used herewith to underscore the interdependence of these issues, as mentioned in all studies. A. Crop Productivity: Research Imperatives (October 1975) This study focused on identifying the fundamental biological processes that control the productivity of economically important food crops and/or the utiliza­ tion of non-renewable resources. It was sponsored by Michigan State University, the Charles F. Kettering Foundation with the support of the U. S. National Science Foundation, the Energy Research and Development Administration, the U. S. Depart­ ment of Agriculture and USAID. A total of 96 scientists, mostly U.S.-based, par­ ticipated in the working sessions that dealt specifically with plant nutrition (nitrogen input; water, soil and mineral input; and environmental stress). A total of 20 priority research components are identified in Table 17 under the heading "M-K 1975." The proceedings are published in a book edited by Brown et aK, 1975). B. Cornell-National Science Foundation (1976) A study entitled "Potential Increases in Food Supply Through Research in Agriculture" was conducted by Cornell University with the participation of 16 scientists, mostly U.S.-based. Two volumes relevant to plant nutrition were pro­ duced, "Fertilizers and Increased Food Production" (Lathwell, 1975) and "Research- able Areas Which Have the Potential for Increasing Crop Production" (Ozbun, 1976). A total of 14 priority research components were identified. They are shown in Table 17 under the heading "Cornell 1976." C. FAQ: Improved Use of Plant Nutrients (1977) FAO held an expert consultation in April 1977 to review plant nutrition re­ search and develop a set of recommendations. A total of 34 scientists from dif­ ferent parts of the world participated. Fifteen research priorities are reported in Table 17 under "FAO 1977." A published report is available (FAO, 1978b). D. National Academy of Sciences: World Food and Nutrition Study (1977) A worldwide assessment of food and nutrition was produced by the National Academy of Sciences in response to a request from the President of the United States, arising from the World Food Conference. Working groups on crop produc­ tivity and resources for agriculture identified priorities relevant to plant 34 nutrition. A total of 26 scientists participated in the development of priority profiles relevant to this study. The overall recommendations and the detailed reports of these two work groups are available as separate volumes (NAS, 1977abc). A total of 21 priority research components related to plant nutrition are iden­ tified in Table 17 under the heading "NAS 1977." E. Soil Constraints Conference (1979) This_conference was co-sponsored by IRRI and Cornell University and was held in Los Banos in June 1979 with support from USAID and the German Agency for Tech­ nical Cooperation (GTZ). The specific purpose was to develop priorities for alle­ viating soil-related constraints to food production in the tropics. It was a joint effort of 75 scientists from national institutions from developing and de­ veloped countries as well as from the international centers. The proceedings have been published by IRRI (1980). Two follow-up meetings of a steering committee set to pursue implementation of the priorities have been held. Twenty-five research components are identified in Table 17 under the heading "SCC 1979." These prior- i ties were arranged according to three major agroecologi cal zones. E. North Carolina State University: Soil Management Planning 1979) This USAID-sponsored study aimed at identifying priorities for the new Title XII Program. A total of 197 scientists and administrators from 46 countries repre­ senting 118 different institutions provided inputs. Priorities were developed with the assistance of an External Advisory Panel of international soil scientists. Extensive travel to developing countries was conducted as a major part of the study. A report is available (NCSU, 1979). Twenty-seven research components are shown in Table 17 under "NCSU 1979" but they were arranged into five major agroecological zones in the report. G. Bonn Conference on Agricultural Production (1979) The most recent study was organized and sponsored by the GTZ, the German Foundation for International Development (DSE), the Federal Ministry of Economic Cooperation (BMZ) and the Rockefeller Foundation. The objective was to assess research and development strategies for increasing agricultural production in the 1980‘s and beyond. A total of 63 scientists developed priorities relevant to plant nutrition in the panel on soils, energy, water and biological resources (Wolff, 1979). Background reports prepared prior to the conference are also published (Bentley et al., 1979; Leach, 1979; Hanson, 1979). The unpublished draft report of the soTTs panel (Bentley, 1979) describes a framework of research components by agroecological zones and a set of assessment parameters. A total of 24 priority research components were arranged in terms of five agroecological zones and are shown in Table 17 under "Bonn 1979." .... 35 Table 17. Summary of priority research and development components identified by the seven assessment studies conducted between 1975 and 1979. Priority Assessment Studies* M-K Cornell MS FAC n£5u Bonn Research and Development Components 1975 1976 1977 1977 1979 1979 1979 A. RESOURCE APPRAISAL 1. Soil characterization and classiti cation X X X X 2. Soil classification for plant nutrition X X X X X 3. Soil fertility evaluation X X X X X 4. Fertilizer supplies, price, distribution and use X 5. Fertilizer manufacturing technology X X B. STRESS FACTORS 1. Selection of germplasm tolerant to soil stresses X X X X X X X 2. Management of soil acidity X X X X X X X 3. Sali nity________ X X X X X X X C. NUTRITIONAL CONSTRAINTS 1. Nitrogen fertilizer efficiency X X X X X X X 2. Phosphorus fertilizer management X X X X X 3. Nutrient balance X X X X 4. Sulfur X X X X X 5. Micronutrients X X X X X D. BIOLOGICAL CONSTRAINTS 1. Bioloti cal nitrogen fixation (BNF) X X X X X X X 2. Organic residue utilization X X X X X X X 3. Photosynthetic efficiency X X 4. Rhizosphere effects X X X X X 5. Basic stress physiology and genetics X 36 Table 17 (Continued). Priority Assessment Studies* TFK Cornell NAS TAO 5CC NCSU Bonn Research and Development Components 1975 1976 1977 1977 1979 1979 1979 E. PHYSICAL SOIL CONSTRAINTS 1. Water management in rainfed systems X X X X X 2. Erosion prevention and control X X X X X 3. Mechanical impedance X X X X 4. Land clearing methods X X F. IMPROVED FARMING SYSTEMS 1. Sustained production in Oxisols/UItisols X X X X X 2. Multiple cropping X X X X X X X 3. Agrofores try_____ X X X 4. Intensive fertilization of high value crops X 5. Management of irrigated farming systems in arid areas X X X X 6. Low fertilizer input farm- ing systems X X X X G. TECHNOLOGY TRANSFER 1. Validation and adaptation of research results X X X X X X X 2. Training___________ X X X X X X X 3. Developing fertilizer recommendations X X X 4. Information Services X X *For identification see text. 37 V. RESEARCH AND DEVELOPMENT NEEDS Assembling Table 17 required some necessary interpretation by the writers of this report, as the specific objectives and terminology of the six studies varied. The participation of one or both writers of this report in the last four studies, including related travel, facilitated this task. For more detailed information, the readers may wish to consult the publications of the specific assessment reports (Brown et al., 1975; Lathwell, 1975; Ozbun, 1976; National Academy of Sciences, 1977a5c;TA0, 1978b; NCSU, 1979; Wolff, 1979; Bentley et al_., 1979; Leach, 1979; Hanson, 1979; IRRI, 1980). Table 17 shows considerable agreement as to what are the priority research components related to plant nutrition. The aggregate total of 32 components arising out of six separate studies that identify an average of 21 priorities each is remarkably low. It seems appropriate to consider this list as a consen­ sus of research priorities arising from the opinions of over 300 scientists from more than 50 countries representing more than 150 different institutions around the world. No weighing is given or implied in the ordering of these research components. They are arranged in broad categories, resource appraisal, overcoming stress fac­ tors, mineral nutrition aspects per se, biological aspects, physical aspects, farming systems and technology transfer aspects, in an attempt to group them in a logical but not totally satisfying fashion. It should be emphasized again that the three most recent studies disaggregated these research components by agro- ecological zones, recognizing that priorities differ in different major regions of the developing world, although many cut across geographical regions. The rela­ tive weighting by agroecological zone will be treated in a subsequent chapter. A. Research Components Related to Resource Appraisal All studies have emphasized the need for a better characterization of the land resource base as a prerequisite for tackling plant nutrition problems in the field. Without knowing to a reasonable degree what the soil resources are, it is difficult to develop or transfer technology that would improve plant nutrient utilization. The three 1979 studies recognize three research components that, operating in sequence, carry the assessments of a geographical area to individual farmer fields: 1) Soil survey and classification; 2) interpretation of classifi­ cation terminology in terms of soil-related constraints; and 3) soil fertility evaluation at the farmer's fields. From the chemical input side,the status of fertilizer production, supply and marketing plus the development of improved fer­ tilizer manufacturing technology have been identified as priority research com­ ponents . 1. Soil characterization and classification. Although a soil map of the world has been produced by FA0 at the scale of 1:5 million, much of the data base from developing countries consists of general estimates or exploratory studies (FA0-UNESC0, 1971-1979). More systematic studies are needed in developing areas in order to provide a reasonable assessment of attributes and limitations of the soils. The degree of detail or the methodology used varies with the intended use. Research on how to characterize and classify soils is not considered high priority. The gap consists of the limited geographical coverage at sufficient *i*i.. ___ _ .. 38 detail. Whenever possible, land classification rather than soil classification is more appropriate as it includes also climate, present vegetation and sometimes available infrastructure. Examples of regional studies are CIAT's land resource evaluation of tropical Latin America (Cochrane et al_., 1979) and FAO's agroecolog- ical zones project (FAO, 1978a). The degree of importance of this research com­ ponent varies very much with countries and regions although most developing countries have begun more detailed systematic soil inventories in relation to present and potential land use. Such studies will yield much basic information and require continuing support. Given the diverse methods of analyzing and classifying soils, it has been difficult in the past to transfer basic soil information from one country to another in a way that is readily understood. Within the last decade a major ad­ vancement has been made in the development of quantitative classification systems such as Soil Taxonomy (SCS, 1975) that are based on criteria determined by spe­ cific methodologies. The expanded use of quantitative soil classification provides a common language akin to plant taxonomy. Expanding the use of quantitative clas­ sification systems throughout the developing world is considered a high priority activity (Swindale, 1978; IRRI, 1980). Research on how to improve these systems for better adaptability to tropical areas is in progress by a series of interna­ tional work groups and should continue. 2. Interpretation of soil classification into plant nutrition constraints. Soil classification systems are essentially a way to store morphological, chemical and physical data in a systematic and retrievable fashion. Soil taxa do not di­ rectly identify plant nutrition constraints. Furthermore, classification systems concentrate on the more stable subsoil properties rather than on the highly dynamic topsoil properties. This divergence has resulted in a major communication gap between the soil classification specialists and agronomists who are primarily in­ terested in topsoil properties because they most directly affect plant growth. Quantitative classification systems therefore, need to be translated or inter­ preted into technical systems for plant nutrition purposes. One such attempt is the Fertility Capability Classification System (FCC) which selected out of Soil Taxonomy and topsoil properties a series of parameters that can be routinely analyzed to identify constraints to plant nutrition in a quantitative fashion (Buoi et al_., 1975; Buoi and Nicholaides, 1980). Another approach is to develop ways of~transferring fertility management information from thoroughly classified soils to other soils classified at the same family level (Benchmark Soils Project, 1979). Latest advances in this project indicate that transferability is signifi­ cantly increased when soil test data not included in Soil Taxonomy are incorporated in the analysis (Cady and Silva, 1980). FAO's Framework on Land Evaluation also includes "ability to supply nutrients" as one of its land qualities (FAO, 1976). Significant interaction among these three approaches is taking place. The World Food and Nutrition, Soil Constraints, North Carolina and Bonn studies strongly recommended strengthening research on technical interpretations of soil classifi­ cation systems for plant nutrition purposes and their adaptation to specific farm­ ing systems by national programs. 3. Soil fertility evaluation. The third step in the process of appraising soil resources for plant nutrition purposes is soil fertility evaluation which is often incorrectly referred to as soil testing. Soil fertility evaluation is the process by which plant nutrition constraints of individual farm fields are identi­ fied and fertilizer recommendations are made. Several approaches are in use - ■if Y.HVi u* -> >• \t - , », , 39 throughout the world, but the most widespread are based on soil testing, pland analysis, missing element techniques, fertilizer response trials and frequently a combination of these (Sanchez, 1976). A major review of soil and plant test­ ing as a basis for fertilizer recommendations has been prepared by Cottenie (1978). In most developed countries, soil fertility evaluation services are well developed and constitute one of the foundations of successful agriculture as well as one of the most important means of increasing the efficiency of fer­ tilizer use. In developing countries, one of the most successful programs has been the International Soil Fertility Evaluation and Improvement Program (ISFEIP) which developed simple, low cost procedures and established a network of national soil fertility evaluation services in most countries of Latin America (ISFEIP, 1974; Palencia et al_., 1975; Hunter, 1975; Waugh et al_., 1975). That program terminated in 1975. In tropical Asia, only India~fTas a major national program. Lack of adequate methods for formulating fertilizer recommendations for flooded rice is a major limiting factor in this region, and it even hampers the develop­ ment of soil fertility evaluation services for upland crops in Southeast Asia. In much of Africa the very limited research conducted at adequate rates of fer­ tilization, coupled with the unavailability or very high costs of fertilizers have largely prevented the establishment of workable soil fertility evaluation services, except on certain large scale plantations. The FAO fertilizer program has provided an impressive amount of field fertilizer response da^a, which is now available in computerized form by country. The need to initiate or strengthen soil fertility evaluation services was the most widely mentioned research need by developing country scientists in the North Carolina study. The Cornell, Soil Constraints and Bonn studies have also endorsed the high priority nature of this component. The need for determining the critical levels of plant nutrients of new varieties that are rapidly being developed is a clear prerequisite for improving plant nutrition at the farmers' fields. With the exception of N for which no adequate rapid diagnostic technology is available, the efficiency of utilization of plant nutrients largely depends on the effectiveness of soil fertility evaluation services. The research and development needs vary with the level of development in dif­ ferent countries. Lopes and Sanchez (1980) have listed specific activities for regions or countries with 1) only rudimentary soil fertility evaluation services, 2) operational semiautomated laboratories, calibration and correlation at the greenhouse level, and 3) those with adequate operational facilities and field testing. The "FAO 1977" plant nutrition study placed major emphasis on soil fer­ tility evaluation. 4- Fertilizer supplies, price, distribution and use. Turning to the input side of plant nutrition, the research and development priorities focus on fertili- zers. The World Food and Nutrition Study recognized that some of the main con­ straints to increased fertilizer use in developing countries lie in the limited understanding that planners have about 1) the economic and social factors that persuade farmers to increase food production through increased fertilizer use and 2) the factors that govern fertilizer supplies (NAS, 1977c). This results in cyclic imbalances with major detrimental consequences on food production. NAS study identified five areas of research to alleviate this constraint: The a) Establish a better understanding of the economic and social factors that influence the farmers' use of fertilizers. This includes the inclusion of risk factors in fertilizer response studies. . j\nt, vi-j»—.. . ■ V> . 40 b) Develop improved methods of demand analysis and forecasting of fertilizer use. c) Develop a methodology for reliable fertilizer supply forecasts. d) Develop a system that will collect and transmit reliable informa­ tion cheaply to central points. e) Develop investment analysis tools for policymakers. Since then, country studies made by IFDC have significantly contributed to this direction and such efforts should continue. 5. Fertilizer manufacturing technology. The Michigan-Kettering and National Academy of Sciences studies identified lowering the cost of fertilizer manufactur­ ing as an important research priority in view of the energy limitations of most developing countries and the world as a whole. The main aspects of this research priority identified by NAS (1977c) are: a) Improve ammonia production through coal gasification. b) Develop alternate sources of hydrogen for ammonia production, such as low cost water hydrolysis, thermochemical processes, photoinduced electron transfer processes and the use of waste hydrocarbons. c) Develop an abiological process of fixing nitrogen without using hydrogen. d) Assess accurately the size, quality and economic potential of global reserves of phosphate rock. e) Develop new or improved methods for the mining and beneficia­ ti on of phosphate ores of generally different composition from those found in developed countries, for example, those having high contents of silica, carbonate, iron, aluminum or chlorides. f) Develop improved acidulation technology designed to handle in­ ferior grades of raw materials. g) Develop improved diagnostic techniques to determine the suita­ bility of direct application of phosphate rock to the soil. Other aspects identified since by IFDC (1980) also merit mention: h) Transform prilled urea plants to produce granules of differing size through pan granulation. Granular urea improves physical properties and permits the use of large sizes with slow release properties for rice culture (IFDC, 1980). i) Assess the potential use of lower cost clinker process of phos­ phate rock acidulation which appears promising for relatively remote areas such as the Sahel where small scale plants can satisfy the relatively low but important demand for P. B. Research Components for Alleviating Stress Factors The second major group of research components include those related to alle­ viating widespread soil constraints such as soil acidity, low available soil phos­ phorus levels, salinity and drought. In the past, the conventional approach has been to eradicate such constraints by sufficient liming, superphosphate applica­ tions, drainage and irrigation. In other words, alter the soil to fit the plant's nutritional demands, thereby eliminating or reducing stress factors. In response 41 to the energy crisis, a different approach has been developed based on the concept of using plants that tolerate to a significant degree these soil constraints; in other words, fit the plants to the soil's limitations (Foy and Brown, 1964; Spain et al_ • » 1975). These efforts have caused misconceptions such as the belief that fertilizer-proof" varieties can be developed and that such tolerant plants could "mine the soil of its available nutrients." A recent review on this subject as applied to acid soils shows that the more successful research results are based on the use of tolerant germplasm together with lower rates of fertilizers and lime. This combination produces reasonably high but seldom maximum yields, but has the advantage of approaching the highest yield per unit of plant nutrient input (Sanchez and Salinas, 1981). Three main research components fall into this cate­ gory: Select tolerant germplasm, manage acid soil stresses and manage saline soils. It is relevant to note that the first two research components are mentioned prom­ inently in the seven assessment studies (Table 17). 1. Selection of germplasm tolerant to soil stresses. Research conducted within the last ten years has demonstrated that plant species and varieties differ significantly in their tolerance to excess amounts of available Al, Mn, Fe, B, high electrical conductivity, high organic acid levels as well as to low levels of available P, Ca, Mg, Fe, Zn, Cu and other plant nutrients. The literature has been compiled in several recent reviews (Wright, 1976; Ponnamperuma, 1977; Jung, 1978; Andrew and Kamprath, 1978; Mussel! and Staples, 1979; Sanchez and Salinas, 1981). They provide ample evidence that many of these differences are agronomi cally rele­ vant and many of them are controlled by rather simple gene combinations that allow breeding for tolerance to specific stresses. Acid, inherently infertile soils, mostly classified as Oxisols and Ulti sols cover approximately 43% of the tropics. Acid soil infertility is often due to the combination of individual stress factors,principally Al toxicity, deficiencies of P, Ca and Mg and to a lesser extent Mn toxicity. These stresses interact with each other. Several plant species and varieties are tolerant to two stress factors, such as AT toxicity and low P availability. Selection and breeding efforts have identified several important species of annual food crops, pastures, perennial crops and trees that are generally quite tolerant to acid soil stresses. Sanchez and Salinas (1981) report 51 such species, including cassava, cowpea, upland rice, pigeon pea, coffee, mango, oil palm, rubber, Andropogon gayanus and Stylosanthes guianensis. In addition, acid tolerant varieties of generally sensitive species such as wheat, soybeans, maize and sorghum have been identified. The use of acid tolerant varieties and species decreases the liming requirements often to low rates sufficient to serve as Ca and Mg fertilization. In addition, Al tolerant plants are able to penetrate acid subsoil layers, thereby being able to tap a larger volume of soil and utilize available water in the subsoil. Aluminum tolerant varie­ ties or species therefore, contribute significantly to better soil moisture utili­ zation and enable plants fo withstand better drought stress periods. In the case of legumes, Al tolerance of the rhizobium is as important as Al tolerance of the plant. Fortunately rhizobium strains also differ in their ability to tolerate acid soil stresses (Munns, 1978; Date and Halliday, 1979). Tolerance to the various factors involved in soil salinity (high electrical conductivity, high Na saturation) have similarly been identified, up to the point of identifying tomato varieties capable of growing in dilute salt water (Epstein, 1976). The widespread use of such germplasm would reduce, but not eliminate the need for drainage and gypsum for eliminating salinity and alkalinity. 42 Rice varietal differences in tolerating several stress factors found in flooded soils have been identified by Ponnamperuma (1977). They include tolerance to Fe and B toxicity, Zn, Fe and P deficiency, and high organic acid concentra­ tions. Breeding for multiple stress tolerance has been recommended as a way to fit rice varieties better to specific marginal soils (F. N. Ponnamperuma, personal conmunication). The evidence suggests that joint efforts between soil scientists, plant breeders and microbiologists be expanded and continued in order to identify germ- plasm tolerant to adverse soil conditions throughout the developing world. The main avenues include: a) Characterization of main varieties or ecotypes of the relevant species for an area for their tolerance to adverse soil factors in quantitative terms. Determine the critical levels for each factor beyond which yields are decreased substantially. b) Match these plant critical levels with soil critical levels for deficiencies or toxicities as identified by soil fertility eval­ uation. c) Collect germplasm (plant and rhizobia) that may be tolerant to adverse soil factors and evaluate them. d) Breed for single or multiple soil stress tolerances and combine with other desirable agronomic attributes such as yield potential and seed quality. Breeding for tolerance to soil stresses is in its infancy in comparison with breeding for insect and disease resistance. Special techniques may have to be developed. Nevertheless, breeding for soil stress tolerance has the advantage that the adverse factors do not mutate as pathogens often do. 2. Management of soil acidity. Soil acidity is a major barrier preventing the development of large areas of the humid tropics and acid savanna regions of the world where much of the expected increases in land areas are likely to occur. In tropical America, for example, there are over 700 million hectares affected by Al toxicity, Ca and Mg deficiencies (Sanchez and Cochrane, 1980). Also Mn toxi­ city is locally important. Soils with similar problems are also important in Indonesia, other parts of Southeast Asia and in Central Africa. Although topsoil acidity can be eliminated by liming to neutralize the exchangeable Al at pH 5.5 several economic constraints limit the straightforward solution to a small propor­ tion of the acid soils. The seven assessment studies concur that research efforts should be aimed at developing a package of practices designed to alleviate this major constraint. The following aspects should be considered according to Sanchez and Salinas (1981): a) Identify plant species and varieties tolerant to Al and Mn toxicities. b) Apply enough lime to satisfy Ca and Mg requirements of plants and to decrease Al saturation levels below those that plants cannot tolerate. c) Promote the downward movement of Ca and Mg into the subsoil in order to increase root development. d) Develop practices that prolong the residual effect of liming. e) Prevent the development of secondary acidity. Secondary acidity is that caused by the residual acidity of added fertilizers, particularly N sources, in soils with low buffering capacity. 43 This problem is not only important in acid soils that have been limed, but also in non-acid soils such as those of the semi arid tropics of Africa (IRRI, 1980). Other important constraints also arise when lime use is introduced in new areas. The lime deposits need to be identified and characterized. Crushing equipment for producing a fine grade of calci tic or dolorni tic limestone in the carbonate form is needed. Usually, the only source available in such areas is slaked lime, Ca(0H)2> which is needed for building and road construction. The Ca(0H)2 is a poor liming material because of physical problems, extremely high reactivity and short residual effects. Although no new technology needs to be developed, attention should be given to the composition, chemical form and fine­ ness of limestone production and its transportation to the users. Financing agencies should look at lime and basal phosphate applications as capital improvements and not as inputs to get the first planting underway, The residual effect of appropriate lime applications should last for several years. The use of these amendments, therefore, should be amortized over the period of time they are expected to be effective. 3. Salinity. Three major types of salinity can be distinguished, saline soils in arid areas under irrigation, secondary salinity, and coastal saline soils. The knowledge on how to ameliorate saline soils through irrigation, drainage and gypsum applications is one of the most advanced and quantified aspects of soil science (Soil Salinity Laboratory, 1954). Nevertheless, the application of such knowledge in many irrigation projects of arid regions in the developing world is often clearly inadequate. Technology transfer, with emphasis on training water management specialists is urgently needed in many irrigated areas of the Middle East and South Asia. There are, however, two researchable issues: 1) The relative tolerance of new species and cultivars, 2) use of green manures to ameliorate sodic soils (Bentley, 1979). Secondary salinity is that caused by mismanagement of irrigation water, transforming non-saline soils into saline ones. This problem is very prevalent in the areas previously mentioned and also in small irrigation systems found in the semi arid tropics (IRRI, 1980). Much less is known about coastal salinity areas, many of which could be de­ voted to rice production in Asia. The Soil Constraints Study (IRRI, 1980) sug­ gested the following research topics: a) Demarcate the different kinds of salt-affected soils in wetland regions. b) Determine their dynamics and the variability of their chemical, physical, hydrologic and climatic properties. c) Establish the critical levels for salinity tolerance for impor­ tant food crops and the breeding of varieties for salinity tolerance. d) Develop criteria for determining which saline tracts have poten­ tial for rice and other crops and what the cost/benefit ratios of development would be. 44 C. Research Components for Alleviating Nutritional Cons train ts The third group of priority research components comprise those that are di­ rectly related to the efficiency and availability of plant nutrient elements. Among the 16 essential nutrient elements,the assessment studies assigned pri­ ority attention to N, P, S and micronutrients in general. Also, four studies called attention to the issue of nutrient balance, particularly between K, Mg and Ca. 1. Nitrogen fertilizer efficiency. This research component was not only considered in all seven studies but was given high rankings in all of them. Lack of sufficient N is the most widespread plant nutrient deficiency in terms of land area of any nutrient in the tropics (Sanchez, 1976). Nitrogen is also the most expensive and energy requiring of fertilizer sources and the most widely used. Unlike P and K, N fertilizer needs are difficult to predict quantitatively because the dynamics of inorganic N prevents meaningful soil analysis. It is not surprising therefore, that usually less than half the N applied as fertilizer is recovered by most annual crops. Recovery is substantially lower (about 30%) in poorly managed flooded rice systems where alternating oxidation-reduction accen­ tuate loss mechanisms. Inorganic N tends to surpress biological N fixation in the soil and in nodules of legume roots, thus decreasing the efficiency of this natural source of N. Organic nitrogen additions as manures, crop residues, and compost also affect the efficiency of applied N, but relatively little is known about the interactions between these sources of N. The main areas requiring attention are summarized below, many of which are drawn from the review by Bouldin et al_., (1980) and the conclusions of the various assessment studies. These areas are not relevant to legume plants or to grass/ legume associations where no N fertilization is contemplated. a) Although the basic concepts of N management are well known for most cropping systems, site-specific fine tuning is needed. It is sug­ gested that N management research follow an integrated approach con­ sidering that plant N uptake at a desired yield level is a function of N mineralized from soil organic matter, N mineralized from organic additions (crop residues, legume residues and manures), biological N fixation and fertilizer N. b) An exception to the above statement is the need to understand the basic concepts of N management in intercropped systems. c) Maximize the recycling of N through use of crop residues, rotations or interplantings with legumes, and utilization of organic N. Bouldin et ajL, (1980) described the Chinese experience where 2/3 of the N comes from organic sources, and the possible adaptations and limitations to other areas. d) Quantify loss mechanisms better, particularly leaching in well drained soils, and denitrification and ammonia volatilization in wetlands. e) Evaluate new fertilizer sources and methods of application. An important breakthrough appears to be in the making with the deep placement of urea supergranules in flooded rice soils. Work by IFDC and IRRI indicate that the N efficiency of flooded systems without ideal water control can increase from about 25 to 60% (IFDC, 1980). Similar efforts that evaluate combinations of ni­ trogen sources, placement and timing of application should be encouraged throughout the developing world. 45 2. Phosphorus fertilizer management. Phosphorus deficiency is a widespread problem throughout the tropics, particularly in the humid tropics where the domi­ nant soils are Oxisols and Ultisols, in Vertisols of the semiarid tropics and in Andisols derived from volcanic ash. In addition, most Oxisols, Ultisols and Andisols with loamy or clayey topsoil texture fix large quantities of added P, thereby rendering that nutrient at best only slowly available for plant growth. The residual effects of P fertilization in high-fixing Oxisols and Ultisols, however, can last for many years. For example, an application of 1280 kg P205/ha as triple superphosphate broadcast and incorporated into an Oxisol of Brazil has produced an average of 6.3 tons/ha of corn per crop during the past nine years. Economic analysis assuming a 25% annual interest rate on capital and price:cost ratio of 6.7 kg corn to pay for 1 kg of P205 showed that this alternative was more profitable than smaller yearly applications (Yost et al_., 1979; Sanchez, 1981). As in the case of lime, basal or corrective phosphorus applications should be viewed as a capital investment and financed accordingly. In many cases, socioeconomic constraints impede the application of large quantities of P to high fixing soils. For soils that are both deficient in P and have a high fixation capacity, a phosphorus fertilizer management strategy needs to be devised for major farming systems. The main research components to develop such a strategy are: a) Studies of different sources of P, in order to determine the feasi­ bility of direct application of cheaper phosphorus sources such as locally available phosphate rocks. b) Determine better placement methods, including combinations of banded and broadcast applications. c) Long-term studies on the residual effect of phosphorus applications to evaluate their full economic value. d) Determination of the critical requirements of P by main varieties and plant species both in terms of external (soil) and internal (plant) requirements. e) Selection of plants that utilize more efficiently low levels of available soil phosphorus. f) Determination of the role and potential of endomycorrhizal inocula­ tions for increasing the ability of plants to absorb phosphorus from the soil. g) Elucidation of the interactions between soil amendments and phosphate applications. 3. Nutrient balance. After deficiencies of major nutrient elements such as N, P, K and S are identified and corrected by fertilization or liming, crop yields often do not increase as expected and in many cases decline. One increasingly common reason for such decline is the development of nutritional imbalances, par­ ticularly in soils with low activity clays such as Oxisols, Ultisols, oxic Alfisols, particularly when the topsoils have coarse textures. Correction of K deficiency often causes Mg deficiency because of an improper K/Mg ratio on the exchange com­ plex (NCSU, 1978). Likewise, nitrogen fertilizer applications may induce secondary acidity which, in turn, may reduce availability of other nutrients. These problems are more severe in areas where fertilizers are available only in one or two formu­ lations and one or both have high residual acidity. Nutrient imbalances are partic­ ularly important in the humid tropics, but they are also widespread in soils of the semiarid tropics and acid savannas with low activity clays. Nutrient imbalances are more frequent where only fertilizers are used, or where excessive applications of lime or P are erroneously applied. 46 For each major farming system on soils with low activity clays, the nutrient dynamics need to be determined as a function of time and depth. The effects of recommended fertilizer and lime applications on the status of K, Ca, Mg, S and micronutrients should be determined as well as the critical ratios that indicate imbalances. The possibilities of solving such problems by alterations of fer­ tilizer ratios or by changes in the manufacturing of fertilizers also need to be determined. The imbalances being discussed are not limited to arable or food crops; tree crops and grazing lands may be affected too. Thus, nutrient balance studies should be concerned with the whole nutrient cycles within soils for farm­ ing systems of general importance. 4. Sul fur. This element is of special concern because of the increasing frequency of its deficiency and its relationship to N. The decomposition of or­ ganic matter releases both N and S in plant-available forms with N:S ratio of about 15 to 1. When N fertilizers that contain no S are applied, the ratio of available N to S often increases sharply and plants suffer from lack of suffi­ cient S to produce the normal N:S ratio of 17:1 in their tissues. With some cereals or oilseeds, such imbalances may actually reduce grain yields even though the N fertilization may increase vegetative growth of the crop. Blair et aK, (1980) emphasized that S deficiencies have been reported throughout tFe tropics, although the amount of research is rather limited. The increasing use of lime and phosphate fertilizers may decrease S retention in sur­ face soils and may result in less S available for crop growth. Higher analysis fertilizers manufactured at present are devoid of or low in S and deficiencies will increase unless S is incorporated into the fertilizers. According to Blair et al_. (1980), sulfur fertilization dramatically increases the methionine content o? grain in areas where S is deficient. Priorities for sulfur research are: a) Development of appropriate chemical methods to estimate S availa­ bility. b) Coordinated investigations of the effect of S fertilization on crop yield and quality. c) Selection of varieties which are efficient in the use of S. d) Study S reactions in dryland and wetland soils as to efficiency of fertilizer S sources, leaching and residual values and long­ term effects. e) Methods of incorporating S into fertilizer formulations for use in the tropics. 5. Micronutrients. Deficiencies of Zn, Fe, B, Mn, Cu and Mo are becoming increasingly important constraints in the developing world because 1) the increas­ ing use of NPKS fertilizers raises yield levels and consequently plant micronu­ trient requirements, and 2) the expansion of the agricultural frontier into mar­ ginal soils, where micronutrient limitations are generally more acute. The basic problem is a paucity of information about micronutrient levels in the soil and micronutrient requirements of plants to be grown. The widespread nature of micronutrient deficiencies can be illustrated by comments from recent reviews. Zinc is probably the most limiting micronutrient in terms of areal extent, because it occurs both in acid and calcareous soils. *■*<>——Ifc, I •■ >■•*•.................. . ------------- 47 Sanchez and Cochrane (1980) estimate that 50% of tropical America's land area (approximately 740 million hectares) suffer from Zn deficiency. Large areas de­ voted to lowland rice in Asia are also Zn deficient, including many soils that are kept constantly flooded (Ponnamperuma, 1977). About half of the soils of Brazil are deficient in Mo for legume crops (J. Dobereiner, personal communica­ tion). Poor rhizobiurn-legume symbiosis is often due to unidentified micronu­ trient deficiencies, which lead to pasture degradation (Hutton, 1979). A review by Lopes (1980) notes that Ultisols in the Amazon jungle of Peru are deficient in B, Cu and Mo. Volcanic ash soils, particularly the older ones, are often defi­ cient in Mo.^ Overliming of Enti sols, Oxisols and Ultisols in Africa have resulted in deficiencies of Mn and Zn. On the other hand, Mn toxicity has been observed in the acid Enti sols. Boron deficiencies are extensive in Africa on hydromorphic soils and Alfisols. Molybdenum deficiencies are a problem in acid sandy soils in Africa. Iron deficiencies of paddy rice have been found in the calcareous soils where low organic matter contents limit soil reduction. Deficiencies of micronutrients in legumes must be studied with plants inocu­ lated with rhizobia, because the legume-rhizobia symbiosis often requires more Mo, Fe, Co, S and Ca than the plant itself. Identification and solution of micronutrient deficiencies and problems re­ quire sophisticated laboratory facilities and extensive field experiments. Such investigations should include: a) Determination of soil test or plant tissue critical levels (deficiency, toxicity and balance) of the various micronutrients for the various crops to be grown in a region. b) Correlating micronutrient differences with natural soil classification systems or technical interpretations thereof. c) Determine appropriate rates, timing and methods of applications of the necessary micronutrients, estimating the length of their residual ef­ fects and possible interaction with other plant nutrients. Monitoring of possible buildups of B and Cu that may reach toxic levels should be included. d) Determine appropriate ways of incorporating micronutrients in fer­ tilizer combinations that will be used in micronutrient-deficient areas. D. Research Components for Utilizing Biological Resources The fourth group of research priorities encompasses those that include a direct plant input as a source or expediter or improved plant nutrition. BNF is of overwhelming importance, but other aspects of a more fundamental nature have been identified by the assessment studies. In addition, soil-borne pathogens, including nematodes are important biological constraints. They will not be dis­ cussed in this paper because this constraint is generally considered the province of plant protection. 1. Biological nitrogen fixation (BNF). Among the soil nutrients, only N has a natural Biological mechanism for replacing crop removal and losses by leaching. The unlimited reserves of N in the atmosphere cannot be used by plants directly. But atmospheric N can be transformed into ammonia by N fixing bacteria. Biological N fixation together with photosynthesis are among the key processes re­ sponsible for the maintenance of life on earth. The exploitation of BNF for 48 modern productive agriculture is gaining increasing importance because by using sun energy it replaces fossil fuels in supplying crops with N. The principal mechanism is the legume-rhizobium symbiosis, which unfortunately is not present in cereals or root crops. A second important mechanism is asymbiotic fixation in the soil and rhizosphere of plants, which is of particular importance in flooded soils. Also, the use of Azolla-Anabaena symbiosis between a blue-green algae and an aquatic plant has recently been introduced from Vietnam and China to the rest of the world. The N fixed by Azolla is incorporated into the soil by mixing the plants into the topsoil. A major advance in increasing BNF for marginal soils is the existence of dif­ ferential tolerances by rhizobium strains to adverse soil factors such as soil acidity, salinity, temporary flooding and even high soil N content (Peter Dart, personal communication). Some priority research areas suggested in the Soils Constraints Conference (App et aK, 1980) and by the Bonn study are outlined below: a) Select rhizobium strains to match soils and local cultivars. b) Review the needs for P and Mo fertilization of rhizobia and associated legumes. c) Develop superior yielding varieties of grain legumes more capable of being better partners with improved rhizobia. d) Develop legume-based forage production systems for those soils marginal for food grain production. e) Develop mycorrhizal inoculants for legumes. f) Develop improved methodology for estimating non-symbiotic N fixation. g) Select variant forms of Azolla and blue-green algae suited to specific rice soils. Mention should be made of the possibility of drastically changing the genetic makeup of cereals in order for them to supply sufficient energy to the roots to support symbiotic or associative N fixation. This issue was featured prominently in the earlier studies but not in the three 1979 studies. This is probably a re­ flection of more urgent needs in tropical areas. Such long-term low probability of success research, however, merits continued attention by advanced laboratories around the world, but no longer appears as a high priority item for problem- oriented plant nutrition research in the developing countries. 2. Organic residue utilization. The rising cost of fossil fuels draws atten­ tion to the need to make better use of organic materials from agricultural residues and other sources for supplementing the supply of plant nutrients available from the soil and from inorganic fertilizers. Increasing petroleum costs, however, also increase the demand for organic residues for direct conversion into liquid fuel. Consequently, the competition between agriculture and industry for manures and crop residues is an important consideration. Two important uses of organic materials are in mulching for moisture manage­ ment and the use of green manuring for improvement of soil structure and increase plant nutrient availability. Currently, these potentials are inadequately exploited, The Soils Panel of the Bonn Conference suggested the following areas of research emphasis: 49 a) Improved recycling of organic materials including better col­ lection, conservation and application of organic materials to be returned to the land, such, as crop residues and animal manures. The focus here needs to be on finding out why, with few exceptions, utilization of organic materials has been so inadequate since on superficial examination there is so much promise. The example of China shows that full utilization can lead to the provision of a major portion of plant nutrient re­ quirements in this fashion-even in intensive agriculture. Research is needed to provide knowledge regarding more efficient handling of organic materials and to determine the factors af­ fecting their utilization. b) Evaluations are needed on the comparative benefits of alternative sources of plant nutrients, the interaction between organic and inorganic nutrient inputs, as well as the real costs of using organic materials as fertilizers. c) Research is needed to determine the factors which impede adoption of effective organic materials used in farming systems. Results should lead to improvements in the applicable technologies. 3- Photosynthetic efficiency. Plants capture less than 3% of the solar energy they receive in the process of photosynthesis. The World Food and Nutrition Study suggests that the theoretical maximum is 12% and that both basic laboratory and agronomic research could significantly increase the rate of solar energy conversion. The Michigan-Kettering study and the World Food and Nutrition Study emphasized the following priority aspects (Brown et al_., 1975; NAS, 1977b): a) Slowing photorespiration in C3 crop species. b) Increasing the efficiency of dark respiration. c) Investigating C3 and C4 species differences.. d) Improving plant architecture and transport of photosynthate. This priority area, however, received a rather different agronomic emphasis at the Bonn Study (Wolff, 1979). The suggested areas of work were: a) Appropriate multiple cropping systems for specific environments to take full photosynthetic advantage of available solar energy, soil and water resources. b) Increase the capability of root and tuber crops to store photo­ synthate. c) Breed and select crop plants with improved architecture for capturing solar energy and storing photosynthates. d) Plant well-adapted tree crops that can rely on stored soil moisture and photosynthate reserves to withstand periods of environmental stress. e) Select varieties of crop plants with high tolerance for drought and other environmental stresses. This is the only research component where real divergence was observed among studies as to the means to accomplish the same objective. 4. Rhi-z-o--s-p--h-eT_r_e _e__ff_e_c_ts-. . Five studies identified research on plant-soil micro­ organism interactions (in addition to BNF) as a major priority component. The 50 Michigan-Kettering and World Food and Nutrition Study emphasized a variety of aspects, while the Soil Constraints, North Carolina and Bonn Studies concentrated on the potential of endoniycorrhizal associations. The rhizosphere is an incredibly complex and ever changing region of the soil in which microflora and plant roots interact with each other, This is "where the action is" in terms of plant nutrient uptake because nutrient ions are affected by a different chemical composition from the rest of the soil resulting from root secretions and microbiological activity (NAS, 1977c). Our understanding of this crucial region is limited, aside from BNF. Two major considerations are the poten­ tial increases in nutrient uptake via mycorrhizal associations and a better under­ standing of nutrient uptake in the rhizosphere. Endomycorrhizae enter into symbiosis with roots of most important crop plants. Fungal hyphae act essentially as extension of the plant's root system, increasing the volume of soil from which the plants can absorb relatively immobile nutrients, particularly P. Most annual and perennial crops are mycorrhizal and the benefits of such associations are already taking place. A classic example of cassava, a species that has a very high P requirement in culture solution but a very low re­ quirement in soil culture because of endomycorrhiza infection (Yost and Fox, 1979). The principal research aspects are: a) Develop practical methods of inoculating plants with improved mycorrhiza strains under field conditions. b) Determine whether inoculated strains persist and improve nu- trient uptake. c) Determine the importance of rhizosphere reactions such as "hydrogen leaking" that may affect or improve nutrient up­ take (Israel and Jackson, 1978). 5* Basic stress physiology and genetics. The physiological mechanisms that govern plant tolerance to soil stresses are not sufficiently well understood (Wright, 1976; Jung, 1978). It is known that some varieties require less P for maximum yields than others of the same species but we do not know why. Likewise the inheritance mechanisms of tolerance to adverse soil stresses is not sufficiently documented. Basic research in these aspects have been identified by the Michigan- Kettering study as a priority research component. E. Research Components for Alleviating Physical Soil Constraints Four priority research components for preventing or overcoming soil physical constraints to improved plant nutrition have been identified by the different studies: Improved water management in rainfed farming systems, prevention and co_ n- trol of soil erosion, surface crusting and other mechanical impedances, and land clearing methods. These constraints are receiving increasing attention in the tropics, particularly in areas where physical soil limitations are more critical than chemical, such as in West Africa. Major reviews on the subject have been produced by Greenland and Lai (1977) and Lai and Greenland (1979). 1. Water management in rainfed farming systems. Rainfed farming systems often suffer from temporary periods of water stress because of the vagaries of rainfall distribution during the rainy seasons. The Bonn study notes that the failure to 51 make the most of the available precipitation is exacerbated by losses via runoff, and leaching and the subsequent damage to the environment. Nowhere is this con­ straint more critical than in the semiarid tropics. This region is also fortunate to begin experiencing a breakthrough on how limited and undependable rainfall can be utilized in a way that two good crops can be grown per year where only one mar­ ginal crop could be grown before. ICRISAT's Farming Systems Progralm and related national programs are showing the way for one major soil type, deep Vertisols (Krantz et al_., 1978). Similar technology needs to be developed for areas with different soils, particularly the sandy and plinthic Alfisols of the Sahel and Sudan savanna regions of West Africa. The Bonn Study identified the following aspects as key ones to improve water utilization in rainfed semiarid farming sys­ tems (Wolff, 1979): a) Technologies for collecting, using and conserving water to increase crop production, including "water harvesting." b) Effective surface drainage techniques especially for heavy soils to eliminate excess surface water during periods of intense rainfall and deliver it to storage tanks. c) Adapting animal-drawn equipment to conduct tillage operations at low cost. d) Cooperative efforts by local farmers to develop and manage water­ shed systems, including storage tanks for supplmenetal "crop saving" irrigations. e) Labor intensive technologies for soil, water and crop management by small farmers. 2. Erosion prevention and control. Clearing and cultivation of land exposes the soil "to the erosive effects of wind and rain, and leads to accelerated erosion, reducing the productivity of the soil and causing siltation of streams and reser­ voirs. This, in turn, may result in flood damage downstream. Overgrazing, exploi­ tative logging practices and construction work also lead to accelerated erosion problems. Although the imnediate effects of erosion are most spectacularly visible in the steeplands and the semiarid tropics, it is a phenomenon common to all areas other than those river basins where lowland rice is produced and where carefully controlled water use and distribution systems are well established. Although the damage caused by severe erosion is easy to visualize, development agencies find it difficult to estimate the value of soil conservation programs that will prevent such damage. The basic principles of soil erosion prevention and control are well known and can be summarized in one sentence: Keep the soil covered with a plant canopy at critical times. Much work is needed, however, to translate this principle into viable action in the developing world. Lai (1980) reviewed the impressive amount of existing data on soil erosion losses, particularly in Africa, and noted the depressing fact that very little has been done about preventing them. He expressed the need to become quantitative about erosion losses and proposed the use of the "Y50" parameter, i.e., tons per hectare of soil loss required to decrease yields by 50 percent. Priority should be given not only to preventing erosion but also to reclaim eroded land economically. Research needs are both basic and applied. The basic information currently used in the tropics is that developed in the temperate region. Major differences in climate and soils suggest that it would be mere coincidence if the empirical i*c. Jafl&ù. 52 relationships developed in one climatic region can be directly transferred to the other. The specific research needs outlined by Lai (1980) are: a) Wind erosion, an essentially neglected area in the tropics. b) Develop inexpensive and effective control methods for gully erosion. c) Rainfall parameters affecting erosivity such as drop size, distribution, kinetic energy and momentum of tropical storms should be determined to quantify the erosi vitity of tropical rains. d) Basic and applied aspects of erodibility of key soils. d) Soil management practices to prevent erosion, such as zero tillage. f) Integrated watershed management. In addition, the authors suggest that methods be developed to demonstrate the benefits of soil conservation in the various agroecologi cal zones of the developing world. 3. Mechanical impedance. Different kinds of mechanical impedances seriously affect food production in the tropics. Perhaps the most damaging is the widespread surface crusting or capping common in many soils of the semiarid tropics and to a lesser extent of other regions. Surface crusting can retard or delay seedling emergence and result in poor plant stands. Tillage-induced compaction of the top­ soil often occurs when excessive land preparation takes place on soils without strong granular structure. Subsoil hardpans may also develop as a result of mech­ anical tillage. Articles by Nicou and Charreau (1980) and Taylor (1980) provide an up-to-date review of these limitations, including the soils where they are likely to occur. Nicou and Charreau (1980) note that the soils most susceptible to mech­ anical impedance have topsoils with kaolinitic clay mineralogy, less than 18% clay and probably less than 5% organic matter. They are mostly classified as Alfisols and Ultisols. The main research issues include: a) A better understanding of the process of surface crusting and soil hardening under semiarid tropical conditions in relation to soil characteristics. b) Development of management systems to prevent compaction. In the humid tropics this may include minimum tillage or zero tillage, but the hardness of many soils of the semiarid tropics at the onset of the rainy season requires the use of mechanical tillage. c) Train extension specialists in preventing excessive tillage, particularly with heavy machinery which often pulverizes the soils leading to compaction, runoff and erosion. d) Study the possibility of selecting crop varieties for the ability of their roots to penetrate hard subsoil layers. It should be noted that the danger of laterite or plinthite formation is not men­ tioned as a constraint by any of the seven studies. Tropical soil scientists are well aware of the limited importance of this phenomenon, but unfortunately the popular press often mentions laterization as a major hazard (Sanchez and Buoi, 1975). li-J r— . I rt». 53 4. Land clearing methods. Large scale deforestation is taking place in many humid tropical areas with the use of mechanized land clearing. The rudimentary bulldozer clearing technologies employed are resulting in major physical damage to the soil in terms of topsoil displacement and surface soil compaction. This is particularly evident in certain transmigration areas of Indonesia and in parts of the Amazon. Research conducted in the Amazon and elsewhere shows that the traditional slash and burn method is a better way to clear tropical forests than any mechanized method. With slash and burn, the nutritive value of the ash becomes free fertili­ zer and there is no significant topsoil displacement or compaction problems. Yields of most crops and pasture species are higher in areas cleared by slash and burn than those cleared by bulldozing (Seubert et al., 1977; Sanchez, 1979). The detri­ mental effects often last for several years. Unfortunately it is no longer suffi­ cient to recommend slash and burn clearing because the pressure of land clearing in many areas is so high that it has to be done by mechanized means, are: The main issues a) Develop alternative mechanized land clearing techniques that minimize the damage to soil properties. Combinations of mech­ anized clearing with burning are also worthy of investigation. b) Determine appropriate land preparation and crop establishment methods for sustained production to follow the different clear­ ing methods used. c) Develop management practices for reclaiming abandoned land cleared by mechanical means. d) Train bulldozer operators and colonization project managers oh how to minimize soil damage while clearinq tropical forests. F• Research Components Related to Improving Farming Systems All studies place special emphasis on integrating the information generated into new or improved farming systems capable of sustained and profitable produc­ tion. The choice of farming systems is quite variable within a region and is very dependent on market demand or opportunities, farming tradition and government policies. The invention of new fanning systems is not envisioned by the authors of this report as an appropriate research goal in most circumstances. The improve­ ment of present farming systems by the incorporation of new technology components is usually the most effective approach and is strongly recommended here as a key priority research area. New technology that produces improved plant nutrition must fit with other aspects within a farming system, not only the purely agronomic ones such as pest control, but also socioeconomic ones. The various assessment studies have highlighted six research components as specific areas of attention within the general scope of farming systems. Some will be discussed in less detail than the previous one because many of them are better described within the context of management systems for specific agroecolog­ ica 1 zones. 1. Sustained production in Oxisols and Ultisols. Five of the studies strongly recommend the development of continuous farming systems in acid, infertile soils regions of the humid tropics presently under shifting cultivation. Population pres­ sures are destroying the stability of traditional shifting cultivation systems in ii'i» i — /^--i — 54 much of the humid tropics. The change from shifting cultivation to some form of permanent farming system is probably drastic enough to be considered the develop­ ment of a new farming system. Substantial research has been conducted primarily in the Amazon and in West Africa that demonstrates the feasibility of replacing shifting cultivation with continuous agriculture. Continuous cultivation systems of Ultisols in the Amazon of Peru have been developed by North Carolina State University's Tropical Soils Program in Yurimaguas, Peru where three crops a year are grown continuously with judicious use of plant nutrient input. A total of 20 continuous crops have been grown to date and yields are increasing rather than decreasing because of experience (Sanchez, 1977, 1981; Vaiverde and Bandy, 1981). Examples of long-term livestock production based on grass/legume pastures have also been developed in the Amazon of Peru (Toledo and Morales, 1979). The IITA Fanning Systems Program has also developed means for continuous crop production for West African Alfisols, based primarily on preventing the deterioration of physical soil properties. These two different approaches reflect the differences in constraints between Ultisols of the Amazon and Alfisols of West Africa. In the former case, chemical constraints are the main ones,while in the latter soil physi­ cal constraints predominate. Much of this technology needs to be validated in other areas both in agronomic and economic terms. The specific items are better described with the content of the humid tropics agroecological zone. 2* Multipie cropping. This priority research component was included in all of the studies. The principal issue is to gather more fundamental information as to how plants interact when two or more species are grown at the same time in terms of their nutritional relationships. Although most food crops in Africa are grown in intercropped combination, most of the fertilizer response work has been con­ ducted in monocultures. Much more work is needed on how to fertilize intercropped and other multiple cropped systems. For additional information, the readers are referred to a book edited by Papendick et al_., (1976). 3. Agroforestry. Agroforestry is a general term encompassing the planting of annual crops and/or pastures with trees, either intercropped or in sequence (King and Chandler, 1978). Consideration of this topic as a priority research did not surface until 1979. The increasing importance of agroforestry is partly due to the potential benefits of including tree crops for sustained farming systems in the humid tropical areas with little input, decreasing erosion hazards and the need to counteract the severe deforestation common in many parts of the semiarid tropics and in the steeplands. In the latter two regions, agroforestry is envisioned by many as the main means for alleviating the fuelwood crisis (Hanson, 1979; Leach, 1979). The "agro" part of agroforestry (its food production potential) is also of considerable importance. A recent review of soils research in agroforestry (Mongi and Huxley, 1979) suggested several priority areas, among which the following seem particularly relevant to plant nutrition: a) Determination of nutritional requirements and stress tolerance of potentially important tree crops for agroforestry purposes. b) Identify the most promising combinations of annual crops with tree crops, pastures with tree crops and annual crops/pasture/ tree crop successions for different environments. ■V TROPIC OF CAPRICORN 100° x # TROPIC OF CANCER Figure 1. Location of the five priority agro- ecological zones (from NCSU, 1979). 5c 20°m vX [•ili » m m Humid Tropics M ■«i io Semi arid Tropics EJ è 0 1 <# Acid Savannas I • y o“ Steeplands "^1 <£*> Approximate Scale Along Equator • 0 Wetlands I 147,000,000 o 0 500 1000 1500 km L:; |0' TROPIC OF CAPRICORN 37 20° 75 VII. PRESENT RESEARCH INVOLVEMENT* Various institutions have major involvement in plant nutrition research in developing countries (Table 21). With few exceptions, most portions of the major research components are being addressed by some combination of the IARCs, other international institutes, developed country institutions and national research systems. It is not within the purview of this chapter to detail what is being done in each of the major research areas by all involved national, bilateral and international organizations. If this were attempted, most likely some important contributors would be inadvertently omitted. Rather, this chapter will briefly review the major soil-plant nutrition research activities of selected IARCs, other selected international organizations, developed country institutes and na­ tional institutions. Linkages with other institutes are not mentioned. A. CGIAR System 1. IRRI. Through IRRI's aim to increase and stabilize rice production in the developing countries, it has had major involvement in a) the chemistry of flooded rice soils, b) plant nutrition-soil fertility aspects of rice production, c) evaluating rice tolerance to adverse soil conditions, d) increasing N fertilizer efficiency varieties for rice through its cooperative work with IFDC, and the INSFERR network, e) intensifying cropping in upland and rainfed areas via multiple cropping, f) evaluating biological N fixation by Azolla for rice production, g) validation/ adaptation of research, h) degree and non-degree training of scien­ tists in soil-plant nutrition areas. IRRI's research also is assessing the impact and contribution of different levels of production. IRRI is also involved to a more limited extent with a) soil characterization, b) fertility evaluation, c) saline soils, d) sulfur and micronutrients. 2. CIMMYT. In fulfilling its mandate to improve maize and wheat production in developing countries, CIMMYT has centered more on breeding than on specific soil-plant nutrition research. However, its breeding programs have included adap­ tation to drought and other stresses. Recently, CIMMYT has been attempting to incorporate dwarfing genes in Al-tolerant wheat varieties from Brazil. It has also given top priority in its current wheat program to improved agronomic prac­ tices. Structural changes in the maize plant has enabled it to make more effi­ cient use of soil nutrients and solar energy for grain production. 3. CIAT. The objective of CIAT activities have centered on beef (and pas­ tures), beans, cassava, maize and rice primarily in Latin America. Emphasis is given to acid savannas and steepland areas. A factor-oriented program, the Land Resources one, cuts across commodity lines. CIAT's major involvement in related research activities has been in a) land resource evaluation, b) selecting toler­ ant germplasm, c) management of soil acidity, d) improving P fertilizer efficiency, e) symbiotic biological N fixation f) sustained production in Oxisols/Ultisols, g) low input systems, h) validation/adaptation of research, and i) non-degree and degree training. Other involvement is in a) classification for plant nutrition, b) fertility evaluation, c) sulfur, d) micronutrients, and e) fertilizer recommen­ dations. *The authors acknowledge that there may be omissions, which are unintentional, and invite the reviewers to make suggestions for additions. --------Ai------->• .-~V. 76 4. IITA. In order to address its primary objective of improving the quality and quantity of food crops in the humid lowland tropics, IITA has had major rele­ vant research activities in a) soil characterization, b) selecting tolerant germ- plasm of cassava, yams, grain legumes and cereal grains, c) erosion prevention and control, d) mechanical impedance, e) land clearing, f) sustained production in Oxisols/Ultisols, g) multiple cropping, h) validation/adaptation of research, and i) training non-degree and degree training. BNF is also addressed. IITA1s research concentrates in Africa. 5. CIP. To improve potatoes and potato growing in developing countries, CIP has centered though not exclusively, on plant breeding and control of diseases and insect pests. CIP's soil-plant nutrition related research has focused on selecting germplasm more widely adapted to environmental stress, including that of the hot humid tropics and on training. Work on soil and plant nutrition is not a major part of its core program. 6. ICRISAT. The mandate of ICRISAT is to improve farming systems and water management in the semiarid tropics; it also has primary responsibility for sorghum, pearl millet, pigeon peas, chickpeas and groundnuts. Its major involvement in soil-plant nutrition related research includes a) selecting tolerant germplasm, b) biological nitrogen fixation, c) water management in rainfed systems, d) mech­ anical impedance, 3) multiple cropping, f) validation/adaptation of research, and g) non-degree and degree training. It is also involved to an extent in soil char­ acterization. ICRISAT cooperates closely with CIMMYT, IRAT (France), numerous other developed country institutes and many national institutions. 7. ILCA. The goal of ILCA is to increase animal output through improved production and range management systems. Improved farming systems are a major component of ILCA's research activities. Little work in plant nutrition is in progress. 8. ICARDA. ICARDA's mission is to help increase and stabilize food produc­ tion in the developing countries of the temperate zone with arid or semiarid climates. Its farming systems work is of relevance to soil-plant nutrition re­ search, as would be the biological nitrogen fixation component of its lentil and broad bean programs. The soil, water and nutrient (SWAN) project of ICARDA is investigating moisture, nutrient interactions and fate in xeric environments. 9. IFPRI. In making projections related to food production and needs of developing countries, IFPRI1s projections regarding fertilizer marketing and use are of relevance to the resource appraisal of soil-plant nutrition research. B. Other International Organizations Although many organizations other than those following are involved in some related research activities, those listed were chosen for their overall pertinence to this study. Recognized also are many funding agencies, such as World Bank, UNDP, the regional banks and the foundations, which support soil-plant nutrition research executed by other organizations; however, these funding groups are not covered as the discussion centers on those performing the work. 1. FAQ. The World Soils Map attests FAO's importance and impact in soil characterization. Other major relevant involvements by FAO are: a) Validation/ adaptation of research, b) training, c) fertilizer recommendations, and -v - W5S 77 d) information services, including the CARIS. FAO also is involved with moni­ toring fertilizer marketing and use and utilization of organic residues. FAO has been fostering salinity research. It cooperates with all relevant IARCs, numerous developed country institutes and institutions of virtually every na­ tional government of developing countries. 2. IFDC. The mission of IFDC is to develop appropriate fertilizer tech­ nology and relate know-how to sustain and increase food production in the develop­ ing countries. In fulfilling that mission, IFDCs activities pertinent to this study are a) fertilizer manufacturing technology, b) fertilizer marketing and use, c) N fertilizer efficiency, d) P fertilizer efficiency, e) validation/ adaptation of research, and f) non-degree and degree training. Agronomic re­ search operations in developing countries are carried primarily through IARCs. 3. AVRDC. In its vegetable production research, AVRDC is involved with selecting germplasm tolerant to adverse soil conditions. Training is an impor­ tant relevant component of its programs. 4. _IC_R__A_F . The agroforestry and low input systems work of ICRAF have partic­ ular relevance to research needs identified by the current study. Cooperative work with various international, regional, developed country and national institu­ tions is envisioned. 5. _II_CTAh.is organization attempts to catalyze agricultural research activities in Latin America. Included in these are a) soil characterization, b) NPK fertilizer research, c) erosion prevention and control, d) validation/ adaptation of research, and e) training. Cooperation is with FAO, some developed country institutes, some international centers and virtually all interamerican national research institutions. 6. CATIE. The most relevant research work of Central American-based CATIE to soil-piant nutrition is its intensive multiple cropping program. Also relevant would be its non-degree and degree training program. Cooperation is with several international, developed country and national institutions. C. Developed Country Institutes The most pertinent groups of developed country institutes which are conduct­ ing research related directly to soil-plant nutrition are listed. 1. Western European institutions. Included in this group would be the Land Resource Development Center of the Overseas Development Ministry (UK), Universi­ ties of Reading and Nottingham (UK), GTZ and various universities of Germany, University of Wageningen and the Royal Tropical Institute (Netherlands), GERDAT and ORSTOM (France) and certainly many others. The LRDC, ORSTOM, Wageningen are conducting soil characterization research in developing countries. GERDAT is investigating nutritional constraints, while the University of Reading is looking specifically at P fertilizer efficiency. The Butenhof Station in Germany plays a leading role in potassium research and nutrient balance. Most are involved in vali dati on/adaptation of research, training, both non-degree and degree—many with fertilizer recomnendations. These groups cooperate among themselves with various international, regional, other developed country and national institutions. r - — ;■ —«....... - • -■■=4*4 W 78 2. Pacific institutions. The Universities of Kyoto and Hokkaido and the Tropical Agricultural Research Center of Japan, along with CSIRO and several Australian and New Zealand universities are conducting soil-plant nutrition research and training in developing countries, primarily Asia. 3. North American institutions. A group of U. S. universities comprised from 1972-1978, the Consortium for Soils of the Tropics under USAID financing. Though the group is now disbanded, many of the universities are still actively involved in soil-plant nutrition research. These include the Universities of Cornell, Hawaii, North Carolina State, Prairie View and Puerto Rico. Major per­ tinent activities are a) soil characterization, b) soil classification for plant nutrition, c) fertility evaluation, d) selecting tolerant germplasm, e) manage­ ment of soil acidity, f) N and P fertilizer efficiencies, g) BNF, h) organic residue utilization, i) mechanical impedance, j) land clearing k) sustained pro­ duction in Oxisols/Ultisols, 1) multiple cropping, m) agroforestry, n) low input systems, o) validation/adaptation of research, and p) training, both non-degree and degree. Minor activities involve a) nutrient balance, b) sulfur, and c) micronutrients. Cooperation is among themselves, many IARCs and developing country institutions. Other U. S. universities such as Purdue, Wisconsin, Florida, Minnesota and California (Davis and Riverside) are also actively in­ volved in soil-plant nutrition research in developing countries. Though just beginning, it is relevant to note the existence of the USAID- financed Soil Management Collaborative Research Program which will mount substan­ tial soil-plant nutrition research projects in the humid tropics, semiarid tropics, acid savannas and steeplands. The Universities of Cornell, Hawaii, Kentucky, North Carolina State, Puerto Rico and Texas A & M will be involved in this program under the management of North Carolina State. Research activities will parallel most of those listed in Table 21. Initial cooperation will be with institutions in Peru, Indonesia, Upper Volta, Niger, Brazil, Colombia, Dominican Republic and ICRISAT, CIAT, IRRI and possibly IFDC. Another USAID-financed program relevant to this study is the Soil Management Support Services. It is contracted through the Soil Conservation Service of USDA and provides short-term services upon request to national institutions. Research activities are related to soil characterization and some to nutritional constraint: Various Canadian research activities related to soil-pi ant nutrition are underway in developing countries. Many of those activities are financed by IDRC and CIDA and are carried out by both that agency and contracting Canadian univer­ sities. Collaboration is with IARCs, some developed country institutions and various national institutions. D. National Research Systems Though near impossible to be all inclusive, pertinent institutional research activities related to soil-plant nutrition will be addressed by region. Many national research institutions are quite strong, among which are some in India, Indonesia, Malaysia and Brazil. The old established commodity institutions work­ ing on cash crops have done considerable work in soil-plant nutrition. 1. Asia. Many Asian countries have national institutions which perform re­ search in soil characterization and few are involved in fertility evaluation, soil classification for plant nutrition; several conduct fertilizer marketing and 79 use and fertilizer manufacturing technology research. Some are involved with research for selecting tolerant germplasm. Many are researching increased efficiencies of fertilizers, especially N and P. China is involved in both Azolla research for BNF and organic residues utilization; India has some re- search efforts in the latter. Some Asian countries are researching water management of rainfed systems and multiple cropping. Many conduct validation/ adaptation research, are involved in training and most make some approach at researching fertilizer recommendations. Cooperation is with IRRI, ICRISAT, CIMMYT, CIP, FAO, IFDC, AVRDC and several developed country institutions. 2. Latin America. Most Latin American countries have national institutions involved in soil characterization research, several with fertility evaluation. Virtually all have some type of research on nutritional constraints, especially related to N and P. To the authors' knowledge, only Brazil has an active research program to select varieties tolerant to adverse soil conditions. Several, in­ cluding Brazil and Peru, are researching soil acidity management. Brazil is also researching non-symbiotic N fixation and land clearing. Several are involved in water management research in rainfed systems, some with erosion control, and many with validation/adaptation of research, training and fertilizer recommenda­ tion research. Cooperation is with CIAT, IRRI, FAO, IICA, CATIE, CIP, IFDC and several developed country institutions, including the U. S. universities. 3. Africa. Several African countries have soil characterization research programs, but few research any of the other resource appraisal components. A few are conducting salinity research. Many are conducting NPK fertilizer trials in an effort to demonstrate the value of fertilizers. Some are researching water management in rainfed systems, erosion prevention and control and mechanical im­ pedance. Improved farming systems are researched by a few. Several are involved in validation/adaptation of research; many with training and a few with fertilizer recommendation research. Collaborative work is with IITA,. WARDA, ICRISAT, IRRI, FAO, many European institutions and several other developed country institutions. E. General Remarks From this rather broad brush stroke summarization of current research efforts related to soil-plant nutrition by institutions within the CGIAR system, other international, developed country and national institutions, one is impressed by the fact that, although some gaps certainly exist, soil-plant nutrition research is not neglected. Just as striking is the impression that while many research efforts in soi1 - plant nutrition are being made, they are not conducted in a sufficiently coor­ dinated manner. For instance, inorganic fertilizer trials are conducted in vir­ tually every country of the world, but how coordinated are these? Are the results correlated with soil test values to improve fertilizer recommendations? Are the results accessible to neighboring countries or other countries in a similar agro- ecological zone? Similar questions can be asked of other soil-plant nutrition research, whether much or little research is conducted in that particular compo­ nent. k 80 Table 21. Current major soil-plant nutrition research involvement in developing countries by various institutions. Developed National Other country research institutes Research and Development CGIAR int'l institutes Latin Components System institutes (bilateral) Asia America Africa A. RESOURCE APPRAISAL 1. Soil characterization and classification 2 4 3 2 3 3 2. Soil classification for plant nutrition 1 2 4 1 1 0 3. Soil fertility evaluation 2 3 4 2 3 1 4. Fertilizer supplies, price, distribution and use 4 5 3 3 3 3 5. Fertilizer manufacturing technology 0 5 0 2 2 1 B. STRESS FACTORS 1. Selection of germplasm tolerant to soil stresses 3 2 4 3 3 1 2. Management of soil acidity 4 2 4 1 3 1 3. Salinity 2 3 3 3 3 3 C. NUTRITIONAL CONSTRAINTS 1. Nitrogen fertilizer efficiency 5 5 4 4 3 3 2. Phosphorus fertilizer management 4 4 4 3 4 2 3. Nutrient balance 3 3 3 2 2 1 4. Sulfur 2 3 3 3 3 2 5. Micronutrients 2 3 3 3 3 2 D. BIOLOGICAL CONSTRAINTS 1. Biological nitrogen fixation (BNF) 5 0 5 4 4 1 2. Organic residue utilization 2 2 1 4 1 2 3. Photosynthetic efficiency 1 1 4 0 0 0 4. Rhizosphere effects 2 0 3 0 0 0 5. Basic stress physiology and genetics 4 0 5 1 1 0 • ' —* • ’<*■«« Xii- . 81 Table 21 (Continued). Developed National Other country research institutes Research and Development CGIAR int'l institutes Lati n Components System institutes (bilateral) Asia America Africa E. PHYSICAL SOIL CONSTRAINTS 1. Water management in rainfed systems 5 1 1 3 3 3 2. Erosion prevention and control 4 2 2 3 3 3 3. Mechanical impedance 4 2 3 2 2 3 4. Land clearing methods 4 0 4 1 3 1 F. IMPROVED FARMING SYSTEMS 1. Systained production in Oxisols/Ultisols 4 2 5 1 3 0 2. Multiple cropping 4 2 3 3 3 3 3. Agrofores try_____ 1 2 2 1 1 1 4. Intensive fertilization of high value crops 2 1 2 3 3 3 5. Management of irrigated farming systems in arid areas 1 2 2 3 3 1 6. Low fertilizer input farming systems 2 1 4 3 3 3 G. TECHNOLOGY TRANSFER 1. Validation and adaptation of research results 4 3 3 2 2 1 2. Training____________ 4 4 4 3 3 2 3. Developing fertilizer recommendations 3 4 4 3 3 3 4. Information services 4 4 3 2 2 1 0 - None; 1 - Scattered rudimentary efforts; 2 - Initial or systematic efforts by one or few institutions; 3 - Widespread efforts by several institutions; 4 - One or few recognized leading institutions; 5 - Center of excellence and established network. 82 Vili. APPROACHES FOR TAC/CGIAR CONSIDERATION This study has concentrated thus far on technical aspects related to plant nutrition research without considering institutional aspects other than identify­ ing some of the presently active institutions in Chapter VII. The next step is to address the question whether additional international action is needed and if so, whether it would be appropriate for consj derati on by the CGIAR system. Al­ though the authors of this report are familiar with the history of TAC's deliber­ ations related to this subject, including the TAC priorities paper (TAC, 1979a) they have deliberately carried their analysis up to this point independent from such considerations, relying rather on the major international studies devoted to assessing soil-plant nutrition research priorities. This chapter examines the findings documented in previous ones in terms of possible actions. The authors have used the TAC priorities paper (TAC, 1979a) as a basis for analysis, although recognizing that international initiatives are not necessarily limited to the CGIAF system. A. General Considerations Our analysis confirms the consensus of many TAC documents that plant nutritior research is not a neglected area. The considerable number of institutions involvec in almost all priority research areas shows the existence of widespread efforts. The worldwide priority assessment studies are themselves evidence that there is no neglect about the importance of this issue. The TAC priorities paper also iden­ tified in the plant nutrition section several of the research components as priorit areas: Biological N fixation, fertilizer use efficiency in humid and semi arid tropics, multiple sources of nutrients (paragraph 99). The last item also infers the necessity for a more systematic approach to developing effective soil fertility management systems for farmers in developing countries. In the soils and water section (paragraph 102) TAC recognized that additional international support may be warranted in soil characterization and inventories, low input systems for acid infertile soils, soil and water conservation in rainfed semiarid areas, and crop tolerance to soil stresses. The same paper (paragraph 90) identified what we call the humid tropics, semiarid tropics and acid savannas as among the most difficult environments for sustained food production and agricultural development. 1. Soil-piant nutrition as factor-oriented research. The worldwide priority studies have emphasized the need to consider factors affecting plant nutrition jointly with plant nutrition per se. Plant nutrition can be viewed as how to pro­ vide and maximize efficiency of nutrient inputs to plants. The authors of this study suggest that consideration of constraints affecting the efficiencies of in­ puts might be a more appropriate factor to consider. We would, therefore, suggest that international attention be given to soil-piant nutrition constraints together, particularly those related to rainfed systems in priority agroecological zones. In essence, we suggest that instead of partitioning the overall area into "plant nutrition" and "soil and water," a more appropriate division would be "soil-plant nutrition" and "water management." Soil-piant nutrition would address primarily rainfed systems where soil-related constraints are the most limiting to food pro­ duction. Water management would address the factors related to irrigated agricul­ ture where the main constraint is the management of irrigation water. It is ob­ vious that water management is important in rainfed systems and that soil-plant nutrition is important in irrigated systems. Breaking a continuum, however, is 83 seldom totally satisfactory. Nevertheless, the division according to what kinds of problems are most important deserves consideration. 2. Location specificity. The issue of location specificity must also be addressed-! Soil-plant nutrition aspects are sometimes considered so location- specific as to warrant only limited international attention. Cognizance of the great variability in soil properties at the local level and the need to tailor- make fertilizer recommendations for individual farmer fields has contributed to this belief. Tn the opinion of the authors, soil-plant nutrition research is no more location-specific than farming systems research. The distinction between the kinds of problems and the degree of manifestation of them is important. The priority research components identified for each agroecologi cal zone address kinds of problems that are so widespread and pervasive that they warrant inter- national attention. The degree of manifestation of the problem varies tremendously hence our emphasis on the need for resource appraisal. Research on how to trans­ fer soil-plant nutrition technology to farmers has been identified as a priority; proper training of soil management specialists to aid this regional and local task is vital. International attention to problems of soil fertility evaluation is warranted as the way to overcome location specificity limitations. In a way, the problems are no different from the ones commodity-oriented IARCs faced in produc­ ing improved germplasm that had to be tailored to specific regions. Methodology problems have been overcome by those IARCs by a series of means, including wide­ spread field testing by national institutions. 3. Need for international effort. Considering the research needs (Chapter V) and proposed framework (Chapter VI) in relation to ongoing work (Chapter VII), the authors conclude that although considerable activity is taking place, the magnitude of the effort and the spotty geographical distribution are clearly insufficient to provide a reasonable degree of certainty that technology for alleviating soil-plant nutrition constraints will be adequately developed and transferred in order to per­ mit continuing increases in food production. A strengthening of the worldwide effort is necessary as has been articulated by the scientists and administrators who participated in the Soil Constraints and Bonn conferences. The 1979 TAC priorities paper (paragraph 17) stated that "priorities for in­ ternational research may gradually become the common denominator of national re­ quirements for international activities, which may complement and support their own national research programs." This statement is directly applicable to an in­ ternational effort on soil-plant nutrition research. It is also relevant to point out that the criteria used in assessing priority agroecologi cal zones and the main research components described in Chapter VI are quite similar to the various quan­ titative and qualitative criteria outlined in the 1979 TAC priorities paper. The authors, therefore, suggest that international effort on soil-plant nutri­ tion research, along the framework outline in Chapter VI, is warranted and neces­ sary to: a) increase the efficiency of plant nutrient inputs, b) increase and stabilize food production in the developing countries and c) conserve the land resource base, particularly in the priority agroecologi cal zonés. Such factor- oriented research is suggested for TAC/CGIAR consideration. The principal international need is to provide a focal point for strengthen­ ing, catalyzing and increasing the quantity and quality of soil-plant nutrition research in the crucial agroecologi cal zones of the developing world. 84 B. Institutional Approaches Three institutional approaches are outlined below as possible TAC/CGIAR actions in soil-plant nutrition research; these range from strengthening those research efforts in existing international organizations to specific new initia- ti ves. 1.. Strengthen soil-plant nutrition research in existing organizations. The first institutional approach is for TAC/CGIAR to strengthen soil-plant nutrition research efforts of the IARC and to encourage strengthening of such efforts of national, bilateral and other international organizations. The IARCs have tended to emphasize the location-specific nature of plant nutrition, but have not ap­ proached the problem with the kind-degree philosophy detailed in this paper. It is suggested as future priorities are addressed by the IARCs that soil-piant nutri­ tion research be strengthened. The IARCs should be centers of excellence not only in developing improved germplasm, but also in developing germplasm tolerant to adverse soil conditions, and in relating crop performance to soil environmental parameters. Examples of such efforts would be strengthening the CIMMYT breedinq -° dWarf A1“t(?lerant wheat varieties of Brazil, and encouraging the IARCs to increase efforts in characterizing soil constraints as related to their ?u°9r?rtÌ1iCal,JCnmmodity or farmin9 systems mandates, perhaps along the approach of the CIAT Land Resources Evaluation Program, in order to generate more basic infor- mation of value to them all. The TAC (1979) priorities paper also mentioned some specific areas of emphasis.such as rice production problems in marginal soils and adaptation of wheat_and maize to marginal soil areas, as well as generally more attention fo biologica N fixation, fertilizer use efficiency, and multiple sources 3 .Certainly> strengthening research efforts such as those of IRRI (and IFDC) in increasing N fertilizer efficiency in flooded rice would be bene­ ficial. Although IFDC is nota CGIAR center, emphasis should be given to the contin­ uation of its program on improving fertilizer manufacturing technology for develop­ ing countries, improving nutrient efficiencies by combining new or different fer- s°ulCces «1th relevant agronomic practices, and monitoring fertilizer supply and demand in various countries. In these efforts, IFDC occupies a unique role which is providing and should continue to provide critical backstopping and support to the present and future soil-piant nutrition research efforts of the IARCs and other organizations. Additionally, IFDC has no vested profit motive in its efforts ° ^mProve ferti 11 zer manufacturing technologies in developing countries. IFDC occupies a pivotal and unique role in soil-plant nutrition Thus, developing countries. research for the . .The of .this. r.eport concur with the observations made by the TAC (1979b) mission to IFDC. Their visit in November 1980 convinced them that this center acts essentially as an imRo in terms of well-defined focus, excellence of staff, sense of urgency, quality of the work, mix of research and training, and good rapport with national institutes. The authors of this report recommend that IFDC continue and ®xpa™Jjuch activities and that appropriate long-term support be provided in order for IFDC to carry on its unique mandate. rndivitìual CGIAR members likewise should stimulate the increasing involvement of their highly qualified universities and research institutes in cooperative work w^h national research systems in the developing countries as well as with the IARCs. Such increased collaboration could add depth to the limited sently involved in soil-plant nutrition research at the IARCs and personnel pre- research systems. many national 85 2. Develop a coordinating center. A second institutional approach consists of creating a coordinating type center under the auspices of CGIAR to catalyze, coordinate and stimulate soil-plant nutrition research in the developing coun­ tries. Such a center is envisioned to encompass the actions under the first in­ stitutional approach. The coordinating center concept is not new and has been developing gradually since 1972. Swindale (1980) has reviewed the history of efforts toward an internationally coordinated program for research on soil factors constraining food production in the tropics. The participants at the Soil Con­ straints Conference resolved that such a coordinating center be established and appointed an international steering conmittee to further study the idea. The steering committee indicated the following objectives for such a center or board: "a) To strengthen national research capabilities to remove soil constraints to agricultural production; b) to coordinate and stimulate the application of soil research results already available through transfers of science and technology; c) to coordinate and promote research on the relationships be­ tween land characteristics and crop performance; d) to enable a sharing of the workload in international soil research and to prevent duplication of efforts; e) to support and initiate training activities—both at the national and international level--aimed at solving soil- related constraints; f) to promote the optimization of land use in the tropics, with special reference to soil and water conservation; g) to identify soil research needs and to mobilize resources to fill gaps; h) to compile, collate, store, stratify, process, retrieve, translate and disseminate soil research results through data processing systems; and i) to recommend action on research priorities which are recognized to require urgent action in support of the international endeavor to free the world from hunger. Considering the complexity and breadth of research components involved, the center would work through international networks each of which would focus on a selected priority. Such a decentralized approach would ensure full involvement of the international research community, allow for geographical coverage and take advantage of resources already available in national and international institu­ tions. The center would be serviced by a small secretariat." One of the salient features of such a mechanism is that it would build on present capabilities throughout the world rather than requiring major capital out­ lays for physical plant at a specific location. A small, but well-qualified pro­ fessional staff would perform the service functions, while most of the field work will be conducted by scientists at different sites along the priority agroecologi- cal zones of the world. 3. Establish an international soil-plant nutrition research institute. A third institutional approach would be the creation of a major institute with ade­ quate facilities to serve as a center of excellence of soil-piant nutrition re­ search for the developing world. Such a center could be located in one of the 86 priority agroecological zones of the world, preferably where rainfed systems pre- dominate. Neither is this a new idea. Bentley (1978) proposed the creation of such a center, stating that the location-specific problems resulting from its location could be overcome by the use of modern methodologies. The TAC study took note of this proposal but did not award high priority to it (TAC, 1979a). C. Considerations for Evaluating Approaches The three approaches differ substantially in their nature and level of operation. They are not mutually exclusive. For example, the functions of a coordinating center would include the activities proposed in the first approach. Although TAC has acted on one of them previously, the authors of this report sug­ gest that all be reexamined in light of the proposed framework described in Chapter VI, instead of being viewed as a previous proposal to strengthen soil science and plant nutrition. In its determinations, TAC may wish to keep several considerations in mind. For example, 1. Which approach would provide maximum utilization of present capabilities and strengthen national efforts most effectively? 2. What are the start-up and operating costs of a long-term effort for each approach? 3. What is the opportunity cost of each approach? The CGIAR (1980) integrative report included a thought in its paragraph 69 that the authors consider a fitting end of this report. "Stating the problems of agricultural development is relatively easy. Developing a research strategy in which international, regional, bila­ teral and national research programs can each play their appropriate role, is fraught with difficulties. 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