Home-produced fertilizers for Africa ?
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CTA. 1992. Home-produced fertilizers for Africa ?. Spore 42. CTA, Wageningen, The Netherlands.
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In less than 50 years Africa has changed from a food exporting region to being the largest importer of food worldwide. An increase in the use of fertilizers could help to rectify this situation but imported fertilizers are expensive to purchase and...
In less than 50 years Africa has changed from a food exporting region to being the largest importer of food worldwide. An increase in the use of fertilizers could help to rectify this situation but imported fertilizers are expensive to purchase and to transport to remote rural areas. The use of locally-available supplies, on the other hand, would transform the availability and cost of the much-needed plant nutrients. Throughout Africa crop production is constrained by low-fertility soils and even with adequate moisture soil nutrient levels are invariably insufficient for crops to express their full yield potential. Compost and manure can help maintain soil fertility but only by removing nutrients from elsewhere. Nitrogen-fixing plants can add nutrients to the soil, but even they contribute relatively small quantities of nitrogen and should be seen as a complement to fertilizer nitrogen rather than a substitute (see Spore No.40 'Azolla for rice'). In addition to nitrogen, plants require a range of major and minor nutrients including phosphorus, potash, sulphur, calcium, magnesium, manganese and boron. A fertilizer demonstration programme organized by FAO over a decade ago showed that on traditional African farms nitrogen is almost always the nutrient which most limits crop yield; phosphorus is a close second. Potash deficiencies are more localized, but sulphur deficiency is now widely recognized as being as important as nitrogen and phosphorus in many areas. Several African countries have reserves of oil or natural gas which are sufficient to produce ammonia for nitrogen fertilizers, and some are using them for this purpose. Countries that have excess hydro-electric power can produce ammonia by the electrolytic hydrogen process. However, low rainfall has reduced water levels in major hydro-electric dams and they have had little surplus electricity after meeting the soaring industrial and domestic demand. Fertilizer resources in Africa According to the International Fertilizer Development Center - Africa, there are agromineral deposits throughout West Africa that may have potential as indigenous sources of plant nutrients. IFDC-Africa has launched a programme to start the long and arduous process of identifying these deposits and developing proposals for research projects to examine the agronomic and economic feasibility of using these materials (mainly phosphatic) as sources of nutrients for food production. IFDC-Africa will establish a database on West African deposits of phosphate, sulphur, lime, gypsum and dolomite. Phosphate deposits have been found in 36 African countries: the main producers are Algeria, Côte d'lvoire, Egypt, Morocco, Nigeria, Senegal, South Africa, Tanzania, Tunisia and Zimbabwe. Of the ACP countries, only Senegal and Zimbabwe produce sufficient phosphate for export. Several countries have indigenous ores which present processing problems, although some of those which prove unsuited to chemical processing might be suited to direct application. Fertilizer production Zambia is one country where locally-available phosphate rocks could, in theory, reduce the need for imported phosphatic fertilizers, the annual requirement for which is over 30,000t. A local company, Mining Exploration (MINEX), has carried out tests using acidulation on low grade areas to make Partially Acidulated Phosphate Rock (PAPR), which has been used successfully on maize and soya beans. MINEX has also shown that where residual brown soils, resulting from the weathering of carbonates, are washed the coating of iron oxide is removed and ores of 10% grade can be enriched to 30% phosphorus. This technique looks promising but the washing process requires large volumes of water: and water is in short supply in this region. There is virtually no production of potash in Africa although resources are reported to exist in more than ten countries. Solar evaporation of potash brines could provide a possible source in several countries. National options Faced with insufficient foreign exchange and transport difficulties almost all African ACP countries must develop whatever local resources are available for enhancing soil fertility. Preventing soil erosion and avoiding the burning of crop residues will reduce the loss of soil nutrients, and composting crop wastes and integrating nitrogen-fixing crops and trees into farming systems will go some way towards meeting crop requirements. Research is needed into simple, low-cost processing of low-grade rocks into utilizable fertilizers. Where deposits are too small for large-scale commercial exploration, they can still be useful regionally or locally. And where labour-intensive extraction and processing is the only alternative, this can be seen as a source of employment for rural people in slack seasons. In the final analysis government planning must recognize that the central position of food production in national economies demands that more resources be directed to all activities that can increase food production, including the utilization of all local resources for fertilizer production: oil and natural gas, hydro-electricity and native ore deposits. For further information contact IFDC-Africa BP 4483 Lome, TOGO
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