Hindawi
Applied and Environmental Soil Science
Volume 2020, Article ID 8818922, 14 pages
https://doi.org/10.1155/2020/8818922
Research Article
Influences of Farming Practices on Soil Properties and the
2-Acetyl-1-pyrroline Content of Khao Dawk Mali 105 Rice Grains
Kawiporn Chinachanta ,1,2 Laetitia Herrmann ,3 Didier Lesueur ,3,4,5,6
Sakda Jongkaewwattana,2 Choochad Santasup,2 and Arawan Shutsrirung 2
1Doctor of Philosophy Program in Environmental Soil Science, Graduate School, Chiang Mai University,
Chiang Mai 50200, #ailand
2Department of Plant and Soil Sciences, Faculty of Agriculture, Chiang Mai University, Chiang Mai 50200, #ailand
3Alliance of Bioversity International and Centre International d’Agriculture Tropicale (CIAT), Asia hub,
Common Microbial Biotechnology Platform (CMBP), Hanoi, Vietnam
4Centre de Cooperation Internationale en Recherche Agronomique pour le Developpement (CIRAD), UMR Eco&Sols,
Hanoi, Vietnam
5Eco&Sols, University of Montpellier (UMR), CIRAD, Institut National de la Recherche Agronomique (INRAE),
Institut de Recherche pour le Development (IRD), Montpellier SupAgro, 34060 Montpellier, France
6School of Life and Environmental Sciences, Faculty of Science, Engineering and Built Environment–Deakin University,
Melbourne, VIC 3125, Australia
Correspondence should be addressed to Arawan Shutsrirung; arawan.s@cmu.ac.th
Received 27 May 2020; Revised 12 November 2020; Accepted 29 November 2020; Published 21 December 2020
Academic Editor: Maman Turjaman
Copyright © 2020Kawiporn Chinachanta et al.)is is an open access article distributed under the Creative CommonsAttribution
License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is
properly cited.
Khao Dawk Mali 105 (KDML105) is a premium fragrant rice variety and is widely grown in )ung Kula Rong Hai (TKR),
northeast )ailand. In the present study, the influence of organic and conventional rice farming (ORF and CRF, respectively) in
TKR farmers’ paddy fields on soil properties and their relationship with 2-acetyl-1-pyrroline (2AP) in KDML105 rice grains were
investigated. )e results indicated that the ORF system had a strong positive effect on major soil quality indicators and the 2AP
content in the rice grains. )e soil organic matter (SOM) was approximately twice as much in the ORF than in the CRF system,
thus leading tomuch higher total nitrogen (TN), humic acid (HA), andmicrobial populations in the ORF system.)e higher SOM
in the ORF system not only enhanced the soil quality indicators but also contributed to approximately 3.5 times higher 2AP than
in the CRF system. Principle component analysis indicated a close correlation among SOM, TN, HA, and microbial population
under the ORF system; these variables exhibited strong correlations with the 2AP contents in KDML105 rice grains.
1. Introduction )e 2-acetyl-1-pyrroline (2AP) aroma compound was first
determined in 1983; since then, it has been considered as the
)ai aromatic rice, especially the Khao Dawk Mali 105 most significant aroma compound in rice [1], including in the
(KDML105) cultivar, is the most popular rice type globally, KDML105 variety. )ere are many factors that affect the
owing to its high cooking quality and unique aroma. )e strength of rice aroma, such as soil properties, genetic con-
KDML105 variety was declared the world’s best rice at the ditions, light intensity, and climatic conditions [2–4]. Different
World Rice Conference held in Macau in 2017. )e price of fragrant rice varieties grown around the world have different
KDML105 in the international rice market is almost double aroma levels. Among these varieties, the KDML105 (Jasmine
that of other rice cultivars.)e volatile aromatic compounds of rice), Italian, and Basmati rice varieties contain quite high 2AP
KDML105 have been studied extensively by many researchers. levels. In addition to the rice genotype, certain growing
2 Applied and Environmental Soil Science
environment characteristics such as soil salinity, soil nutrients, rice fields) in TKR and neighbouring areas of Surin and
drought conditions, storage time and temperature, planting Yasothon provinces, well-known rice growing areas, were
density, and harvesting time exert considerable effects on selected for soil and rice grain sampling. )e ORF paddy
aroma strength and quality [4, 5]. Low density and early fields have been registered as organic for around 5 years.)e
harvesting have been shown to improve the aroma content and rice in CRF paddy fields has been cultivated for 15 years.)e
other seed qualities [6, 7]. ORF was maintained under the )ai Organic Agricultural
Although the KDML105 rice variety is widely grown Standard (TAS 9000–2009) with the application of com-
throughout )ailand, at present, the most premium quality posted manure (625 kg ha−1) and green manures. )e CRF
of the variety in terms of unique aroma and 2AP quantity is was practiced under the )ai Agricultural Standard (TAS
produced in the )ung Kula Rong Hai (TKR) area. TKR is 4400–2009) with the application of chemical fertilizers: 46-0-
located in the centre of northeast)ailand and covers a wide 0 (93.8 kg ha−1) and 16-16-8 (156.2 kg ha−1).
plain area of 2.1 million rai that extends across five prov- )e samples used in this study were collected from the
inces, namely, Roi Et, Maha Sarakham, Surin, Yasothon, and farmers’ field during the dry season before the rice harvest
Srisaket. Approximately 46% of the area belongs to Roi Et (November 2018). Rhizosphere soil samples were randomly
Province. )e TKR region is underlain with tremendous collected (0–15 cm deep), in 10 spots per composite soil
rock salt layers of the Maha Sarakham formation (mainly sample. Each sample was divided into two parts. One part
halite (NaCl)), which cause major problems for agricultural was preserved in field-moist condition and was used for
activities. In addition, the soils are sandy, acidic, and infertile microbial analysis, and the other was air-dried for physi-
[8]. Soil quality improvement has been carried out in TKR by cochemical analysis. Rice grain samples were also collected
the Land Development Department since 1981. Currently, from the same 18 sites. )e 18 sites extended over five
the KDML105 rice variety produced in the TKR region is provinces (Roi Et, Maha Sarakham, Surin, Yasothon, and
well known for its premium quality, unique taste, and Srisaket) (Figure 1).
distinct smell. A number of studies have been undertaken for
more than a decade to understand the factors that affect the
unique taste and aroma of the KDML105 rice variety; 2.2. Soil PropertyAnalysis. )e soil texture, pH, and EC were
however, to date, scientists have not yet reached a definitive analysed by the standard method [12, 13]. )e cation-ex-
conclusion. It has been assumed that the KDML105 rice change capacity (CEC) was determined using the leaching
quality is highly influenced by the photoperiod, wet and dry method [14, 15]. Humic acids (HA) were determined using
conditions, climate, and soil nutrients of TKR. )e com- the method of Ahmed et al. [16] and Palanivell et al. [17].)e
bination of stress during rice cultivation in TKR may soil organic matter (SOM) was determined using the
stimulate the rice to respond by producing proline sub- Walkley–Black method [18]. )e total N (TN) content of the
stances, which are the precursors of the aromatic substance soils was determined using the modified micro-Kjeldahl
(2AP) of KDML105. In addition, the concentration of 2AP is digestion method [17]. Phosphorus (P) and sulphate (S)
influenced by interactions between the rice genotype and were extracted by Bray II and Ca(H2PO4)2 in 2N HOAc,
environmental factors, such as soil fertility and abiotic stress. respectively, and determined by using a spectrophotometer
Under high soil salinity, KDML105 cells accumulate Na+, [19, 20].)e exchangeable bases, i.e., potassium (K), calcium
leading to proline and 2AP increases in the rice grains. (Ca), and magnesium (Mg), were extracted with 1N am-
Osmoprotectant proline has been found to be the precursor monium acetate (NH4OAc) and determined by atomic
and the nitrogen (N) source of 2AP in KDML105 [9]. High absorption spectrophotometry [21].
total soil N increases the 2AP content in grains [10]. Some
micronutrients such as Mn, Si, and Zn also appear to be 2.3. Determination of the Microbial Population. Exactly 10 g
related to 2AP levels in aromatic rice [11]. of each soil sample was mixed into 95mL of sterile distilled
Recently, the aroma quality in the KDML105 and other water and shaken (120 rpm) for 30min. Serial dilutions were
scented rice varieties has undergone a gradual degradation.)e prepared, and 0.1mL aliquots (103–105) were spread on agar
progressive reduction in the 2AP levels of KDML105 may be media plates. Egg albumin and rose bengal agar medium
due to soil quality degradation caused by high agrochemical [22] plates were used to measure the total bacterial and
applications in conventional farming. For these reasons, the actinomycetal populations and fungal populations, respec-
objectives of the present study was (1) to determine the soil tively. )e total counts were determined after 3–5 days of
properties of the farmers’ paddy field in the TKR areas incubation.
influenced by organic rice farming (ORF) and conventional
rice farming (CRF), (2) to analyse the 2AP content in KDML
rice grains collected fromORF and CRF, and (3) to analyse the 2.4. Determination of 2AP Content in KDML 105 Rice Grains.
interrelationship between farming practice, soil property, and )e rice grain samples were dried in an oven at 60°C for 3
the 2AP content in KDML 105 rice grains. days until the moisture content was reduced to 14%.)e rice
grain samples were, then, dehusked by hand to yield un-
2. Materials and Methods cooked brown rice seeds before being sent to the Chemistry
Laboratory, Faculty of Science, Chiang Mai University,
2.1. Soil andRiceGrain Sampling. Eighteen farmers’ rain-fed )ailand, for the determination of the 2AP content by the
paddy fields (nine organic and nine conventional KDML105 method of Wongpornchai et al. [23].
Applied and Environmental Soil Science 3
10330′00″E 10430′00″E
Maha sarakham ROI Et
Yasothon
Buriram
Surin SI Saket
10330′00″E 10430′00″E
(i) Organic rice farming
(ii) Conventional rice farming
Figure 1: Eighteen sampling sites in the Tung Kula Rong Hai region and neighbouring areas of Surin and Yasothon provinces.
2.5. StatisticalAnalysis. )e data were compared statistically percentages under the same soil texture were similar in the
by analysis of variance (ANOVA) with Duncan’s multiple two farming practices (ORF and CRF) (Figure 2). In general,
range test at the 0.05 probability level in Statistix 8.0. soil texture is a fixed characteristic and cannot be changed
Arithmetic means were calculated for each of the three unless a significant volume of these components is added or
replicates separately. )e obtained data were analysed sta- subtracted. )e results of this study confirmed that the
tistically (correlation) using the SPSS Statistics forMac OS X, different farming practices did not change the soil texture.
version 20 (SPSS Inc., Chicago, IL, USA). Principal com- However, soil aggregates bearing on other soil properties
ponent analysis (PCA) was performed to evaluate the re- may be highly affected by the farming practices.
lationships among the different cultivation systems, soil On the average, a slight difference in the pH of paddy
properties, and the 2AP content. Soil parameters including soils was observed between the ORF (4.87) and CRF (5.37)
pH, EC, SOM, HA, CEC, TN, P, K, Ca, Mg, and S and the systems (Figures 3(a) and 3(b); Table 1). Several studies
microbial population, as well as the sand, silt, and clay have shown that soil pH is slightly but not significantly
percentages, were introduced as variables in the PCA using R lower in organic systems compared to conventional
1.2.1335 [24]. systems (on similar soils) [26]. In general, flooding in
acidic paddy soils leads to strongly reducing conditions in
3. Results and Discussion the topsoil and pH increase to near neutrality [27];however, the soil pH decreases after draining [28]. In the
Jasmine rice var. KDML105 is officially one of the best present study, the rhizosphere soils were collected at
aromatic rice varieties because of its unique fragrance. We harvest time when they were almost dry, and then, they
hypothesized that farming practices and soil properties were air-dried before analysis. )erefore, the soil pH of
might affect the aromatic quality of rice grains. )erefore, in ORF and CRF under this study was influenced by farming
the present study, the influence of farming practices in TKR practice rather than submerged conditions.
paddy fields on soil properties and their intercorrelation Most of the EC values of the ORF system (0.54–2.54 dS
−1
with 2AP were investigated. m ) were significantly higher than those of the CRF system
(0.18–1.54 dS m−1) (Figures 3(c) and 3(d)). )e average EC
value of the ORF system (1.25 dS m−1) was much higher than
3.1. Soil Properties Affected by Farming Practice. Sandy soils that of the CRF system (0.53 dS m−1) (Table 1). In the present
are widespread in the TKR region. Some areas have sand- study, the higher EC found in theORF than in the CRF system
stone-derived soils, while in other, soils are severely affected might be affected by organic inputs in the ORF system. Our
by salt [25]. In the present study, most of the soils in the findings are in good agreement with previous works in that
study area (72%) had a sandy texture (loamy sand/sandy organic practices including the addition of green manures,
loam) (Figure 2). )e soil texture of the rest of the locations organic matter, and compost to soils markedly increased the
ranged from loam to silt loam. )e sand, silt, and clay EC values [29–32].
1445′00″N 1545′00″N 1645′00″N
1445′00″N 1545′00″N 1645′00″N
4 Applied and Environmental Soil Science
100
90
80
70
60
50
40
30
20
10
0 ORF ORF ORF ORF CRF CRF ORF CRF CRF CRF ORF ORF ORF CRF ORF CRF CRF CRF
3 4 11 15 5 12 6 7 13 14 1 2 10 16 9 8 17 18
Loamy sand Sandy loam Loam Silt loam
Soil texture
Sand (%)
Silt (%)
Clay (%)
Figure 2: )e proportion of sand, silt, and clay particles in the soil of organic and conventional rice farming (ORF and CRF, respectively)
sites for each soil textural class.
ab a pH
6 abcde abcd abc abc
bcde abcde abcde
abcd 7.50
cde cde cde cde bcde
bcde
5 e de 7.00
4 6.50
3 6.00
2 5.50
5.00
1
4.50
0
1 2 3 4 6 9 10 11 15 5 7 8 12 13 14 16 17 18 4.00
ORF CRF ORF CRF
Farming practices Farming practices
(a) (b)
3.00 EC (dS m
–1)
a 2.50
2.50
2.00
2.00 b bc bcd
1.50 cde 1.50def
1.00 efgfgh gh
ghi gh
1.00
ghi hi ghi
0.50 hi hi i hi 0.50
0.00
1 2 3 4 6 9 10 11 15 5 7 8 12 13 14 16 17 18 0.00
ORF CRF ORF CRF
Farming practices Farming practices
(c) (d)
Figure 3: )e soil pH value (a, b) and electrical conductivity (c, d) of the soils in organic and conventional farming systems (ORF and CRF,
respectively). )e error bars represent the standard deviation of measurements for nine soil samples.
)e amount of SOM in the soil samples was very low to (1.05%) [33]. )e SOM content is influenced by various
quite high, ranging from 0.30% to 2.41%, and the average of factors such as soil texture and farming practices [34, 35].
ORF-SOM (1.41%) was higher than the average of CRF- )e SOM of clay loam and sandy loam in the TKR region is
SOM (0.66%) (Figure 4(a) and 4(b); Table 1). )e SOM of approximately 1.04% and 0.62%, respectively [36], indi-
rain-fed sandy loam in the TRK region is naturally quite low cating the influence of soil texture on SOM. However, with
EC (dS m–1) pH
Percent (%)
Applied and Environmental Soil Science 5
Table 1: Statistical summary of the physicochemical properties and microbial population of the soil for organic and conventional rice
farming systems.
Organic rice farming Conventional rice farming
Variable Unit
Minimum Maximum Mean S.D. Minimum Maximum Mean S.D.
pH 4.36 5.32 4.87 0.31 4.88 5.96 5.41 0.39
EC dS m−1 0.54 2.54 1.25 0.67 0.18 1.54 0.54 0.40
SOM % 0.84 2.41 1.41 0.55 0.30 1.03 0.66 0.23
Humic acid % 1.05 1.78 1.29 0.25 0.24 1.47 0.74 0.40
CEC cmolc kg−1 1.98 7.66 4.22 2.25 1.19 5.15 3.01 1.36
Total N % 0.04 0.12 0.07 0.03 0.02 0.05 0.03 0.01
Avail. P mg kg−1 2.44 37.53 13.68 13.92 2.38 139.16 30.12 45.53
Exch. K mg kg−1 34.08 131.91 73.70 35.57 9.01 159.49 67.28 49.25
Exch. Ca mg kg−1 101.72 1307.35 377.50 376.49 59.00 651.96 262.57 194.36
Exch. Mg mg kg−1 9.46 197.46 42.51 59.53 2.66 31.16 17.79 11.13
Extr. S mg kg−1 9.10 222.99 38.96 69.41 2.53 24.78 10.40 6.11
Sand % 34.90 83.20 64.88 17.86 25.00 80.80 53.49 20.91
Silt % 12.70 53.60 25.68 13.46 15.10 58.30 38.64 17.32
Clay % 4.10 18.20 9.44 5.68 3.20 19.00 7.87 4.93
Bacteria (×105) cfu g−1 80.51 620.60 277.12 186.99 10.12 50.72 22.61 15.78
Actinomycetes (×105) cfu g−1 2.08 23.70 12.98 8.84 0.02 1.56 0.91 0.54
Fungi (×105) cfu g−1 0.42 1.78 1.00 0.37 0.11 0.29 0.22 0.06
a SOM (%)2.50 2.50
2.00 b n b 2.00
1.50 1.50
cd c cd cd
1.00 cdef cdef defg cdecdefg cde
fgh efgh 1.00gh
0.50 h
0.50
0.00
1 2 3 4 6 9 10 11 15 5 7 8 12 13 14 16 17 18 0.00
ORF CRF ORF CRF
Farming practices Farming practices
(a) (b)
a Humic acid %
1.80 ab 2.00
1.60 abcabc 1.80
1.40 abcd
bcd bcd bcd
1.60
1.20 bcd bcde cbe cde cde 1.40
1.00
def 1.20
0.80 1.00
0.60 ef ef 0.80
0.40 f f 0.60
0.20 0.40
0.00 1 2 3 4 6 9 10 11 15 5 7 8 12 13 14 16 17 18 0.20
0.00
ORF CRF ORF CRF
Farming practices Farming practices
(c) (d)
a CEC (cmol  kg
–1
c )8 8
7 b
b
7
6 c c 6
5 c cd
5
4 de
efgh ef efg
3 efgh
4
ghi fgh ghi hi hi
2 3i
1 2
0 1
1 2 3 4 6 9 10 11 15 5 7 8 12 13 14 16 17 18 0
ORF CRF ORF CRF
Farming practices Farming practices
(e) (f )
Figure 4: Soil organic matter (SOM) (a, b), humic acid (c, d), and cation-exchange capacity (CEC) (e, f ) of the soils in organic and
conventional farming (ORF and CRF, respectively). )e error bars represent the standard deviation of measurements for nine soil samples.
Humic acid (%)
CEC (cmol  kg–1) SOM (%)c
6 Applied and Environmental Soil Science
the organic fertilizer application in the ORF system in this respectively (Table 1). In the present study, it appeared that
study, the SOM value in sandy loam and loamy sand under the ORF practice had a positive impact on the Ca, Mg, and S
this system could be as high as 1.9% and 2.41%, respectively amounts, but not on the K amount. )e same trend was
(Figures 2 and 4(a)). )e results demonstrated the higher found with extractable S, with the average value of S in the
impact of organic practices on SOM than the soil texture. ORF system (38.96mg kg−1) being obviously higher than
Under submerged conditions in acidic soils, the pH increase that of the CRF system (10.4mg kg−1) (Figure 6(f)).
is faster in soils with high SOM than in those with low SOM Soil microbes and their functions, particularly SOM
[27]; thus, organic practice would benefit in terms of en- decomposition, humification, and nutrient transformation,
hancing soil buffering capacity in the paddy field. are key factors for the sustainability of soil quality, agri-
)e application of various organic matter types into soils cultural systems, and ecosystem services. )e results of the
increased the amount of humic acid (HA) [37]. HA derived present study showed that the SOM, HA, and TN values
from SOM decomposition is an important fraction in the were obviously higher in the ORF system (Figures 4 and 6).
formation and stability of water-stable aggregates, thus As a result of high SOM, the bacterial, actinomycetal, and
improving the movement of water and air in the soil. In the fungal populations in the rhizosphere soils examined in this
present study, the application of organic matter in the ORF study were much higher in the ORF than in the CRF system
system appeared to increase the SOM and HA content (Figure 7). High bacterial numbers were detected in the ORF
irrespective of the soil texture (Figures 2 and 4). )e average system, with values ranging from 8.51 to 62.6 (×106 cfu g−1).
HA values in the soils of the ORF system (1.29%) were much Much lower bacterial numbers were detected in the CRF
higher than those of the CRF system (0.74%) (Table 1). HA system, with values ranging from 1.17 to 5.72 (×106 cfu g−1)
enhances enzyme activities involved in photosynthetic (Figure 7(a)). )e actinomycetal population ranged from
metabolism in maize leaves [38] and improves rice yields by 2.08 to 23.7 (×105 cfu g−1) and 0.02 to 1.56 (×105 cfu g−1) in
10–20% [39]. In this study, therefore, the high HA in the the ORF and CRF systems, respectively (Figure 7(b)). A
ORF system had a high potential to increase the physico- similar trend was observed in the fungal populations; these
chemical and biological properties of the soil of TKR paddy ranged from 4.19 to 17.8 (×104 cfu g−1) and 1.12 to 2.88
fields, thus also increasing rice yields. (×104 cfu g−1) in ORF and CRF, respectively (Figure 7(c)).
)e cation-exchange capacity (CEC) of soils is mainly )e results were in good agreement with an earlier study that
due to SOM and clay minerals. )e TKR soil is sandy in higher microbial population and activity were recorded in
nature (low SOM and clay contents); therefore, the CEC soils under the ORF than under the CRF system [43].
value of natural TKR soil is quite low (2.31 to Microbes in the rhizosphere can enhance plant growth
7.51 cmol kg−1c ) [33, 40]. )e CEC values of the TKR soils in and immunity by providing secondary metabolites (SMs).
this study are in good agreement with earlier reports with Under stress conditions in rice-growing areas of TKR, high
values ranging from 1.19 to 7.66 cmol kg−1c (Figures 4(e) and rhizosphere microorganisms in the ORF system might
4(f)). )e average CEC values were 4.22 and 3.01 stimulate the production of SMs, particularly 2AP in rice,
(cmol −1c kg ) for the ORF and CRF systems, respectively leading to higher stress tolerance and aroma level in the
(Table 1). On average, the CEC of the ORF system under all grains.
soil textural classes was higher than that of the CRF system,
particularly under the loam and silt loam class. )e results
indicated that the CEC of soils in this study was mainly due 3.2. Correlation between Soil Properties and 2AP in Rice
to SOM and, to a lesser extent, clay mineral (Figure 5). Grains. 2AP has proven to be a potent N-containing aroma
Studies have indicated that the contribution of organic compound in fragrant rice varieties. 2AP is a volatile alkaloid
matter to the total CEC of a soil is usually substantial and is substance in rice that normally accumulates in response to
often considerably greater than that of clay minerals [41]. environmental stress [44]. In the TKR region, the unique
Althoughmore than 80% of the TKR soil is considered as and high 2AP aroma of KDML105 may be due to various
poorly fertile soil [40], our results showed that the ORF stress such as the natural low fertility of sandy soil, the high
practice could improve several nutrients level, particularly salt content, and the water shortage during the rain-fed rice
the total N (TN), as compared to the CRF practice season [40]. )erefore, in this study, we determined the 2AP
(Figure 6(a). )e organic fertilizer application in the ORF concentration in mature rice grains and analysed the rela-
system increased the TN amount (0.037%) by approximately tionship between 2AP and the soil properties of the ORF and
twice as much as that of the CRF system (0.017%) CRF systems.
(Figure 6(a)). An earlier report also indicated that the ap-
plication of compost in a maize-wheat cropping system 3.2.1. 2AP Affected by Farming Practice. Several studies have
increased the initial TN value up to 78–93% [42]. Beside TN, shown that organic inputs not only improve rice soil but also
the average values of exchangeable K, Ca, and Mg were enhance rice quality including 2AP compared to chemical
higher in the ORF system (73.7mg kg−1, 377.5mg kg−1, and fertilizer applications [45, 46]. )e 2AP level in rice grains is
42.51mg kg−1, respectively) than in the CRF system widely used as one of the high-quality indicators of aromatic
(67.3mg kg−1, 262.6.5mg kg−1, and 17.8mg kg−1, respec- rice. In the present study, the 2AP levels of all ORF sites were
tively) (Table 1; Figures 6(c)–6(e)). In contrast, the p values higher than those of the CRF sites (Figure 8(a)). )e 2AP
of the CRF systemwere higher than those of the ORF system, contents of TKR rice grains obtained from the ORF system
with mean values of 30.12mg kg−1 and 13.68mg kg−1, (5.52–13.69mg kg−1) were significantly (p< 0.05) higher
Applied and Environmental Soil Science 7
10
9
8 a
7 b b
6 c c
5 c cd
4 de
efgh efg
ef
3 fgh ghi efghghi hi hi
2 i
1
0
ORF ORF ORF ORF CRF CRF ORF CRF CRF CRF ORF ORF ORF CRF ORF CRF CRF CRF
3 4 11 15 5 12 6 7 13 14 1 2 10 16 9 8 17 18
Farming practices
Loamy sand Sandy loam Loam Silt loam
Soil texture
Figure 5: Cation-exchange capacity (CEC) as influenced by soil texture and farming practices. Note: ORF� organic rice farming;
CRF� conventional rice farming.
Total N (%) Avai. P (mg kg–1) Exch. K (mg kg–1)
0.14 80.00
0.12 70.00
145.00
125.00
0.10 60.00
50.00 105.00
0.08
40.00 85.00
0.06
30.00 65.00
0.04 20.00 45.00
0.02 10.00 25.00
0.00
Organic Conventional 0.00 5.00Organic Conventional Organic Conventional
Farming practices Farming practices Farming practices
(a) (b) (c)
Exch. Ca (mg kg–1) Exch. Mg (mg kg–1) Extr. S (mg kg–1)
640.00 60.00 47.00
540.00 50.00 42.00
37.00
440.00 40.00 32.00
340.00 30.00 27.00
22.00
240.00 20.00 17.00
140.00 10.00 12.00
7.00
40.00 0.00 2.00
Organic Conventional Organic Conventional Organic Conventional
Farming practices Farming practices Farming practices
(d) (e) (f )
Figure 6: Soil mineral concentration (a–f) in soils collected from organic and conventional farming (ORF and CRF, respectively) systems.
)e error bars represent the standard deviation of measurements for nine soil samples.
than those obtained from the CRF system 3.2.2. 2AP Affected by Soil Chemical Properties. Several
(0.49–5.60mg kg−1) (Figures 8(a) and 8(b)). Poomipan et al. studies have shown that soil texture may influence the 2AP
[47] reported that the 2AP in rice grains obtained after level in mature rice grains. An evaluation of 67 soil samples
organic fertilizer application (1.77mg kg−1) was higher than in the TKR region revealed that the level of 2AP in rice grains
that obtained after chemical fertilizer application grown in sandy soils is higher than that in those grown in
(1.46mg kg−1). )e results obtained in this study confirm loamy soils, followed by clayey soils [40]. A higher 2AP
that the ORF system provided much higher 2AP in the rice content was found in rice grains grown in sandy soils
grains over the CRF system. (1.90–3.00mg kg−1) than in those grown in clayey soils
CEC (cmolc kg
–1)
8 Applied and Environmental Soil Science
5 6 –1
70 25 (10 –10  cfu g ) 20
(107 cfu g–1) (104–105 cfu g–1)
18
60
20 16
50 14
15 12
40
10
30 10 8
20 6
5 4
10 (106 cfu g–1) (103–104 cfu g–1) 2
0 0 0
1 2 3 4 6 9 10 11 15 5 7 8 12 13 14 16 17 18 1 2 3 4 6 9 10 11 15 5 7 8 12 13 14 16 17 18 1 2 3 4 6 9 10 11 15 5 7 8 12 13 14 16 17 18
ORF CRF ORF CRF ORF CRF
Farming practices Farming practices Farming practices
(a) (b) (c)
Figure 7: Bacterial (a), actinomycetal (b), and fungal (c) populations in the rice rhizosphere under different cultivation systems. )e error
bars represent the standard deviation of measurements for nine soil samples. Note: ORF� organic rice farming; CRF� conventional rice
farming.
14 a 2APab
b 14.00
12
c c 12.0010
10.00
8 dde d
ef ef 8.006 f
g 6.00
4 gh hi
jk ijk hij 4.002 k
2.00
0
1 2 3 4 6 9 10 11 15 5 7 8 12 13 14 16 17 18 0.00
ORF CRF Organic Conventional
Farming practices
(a) (b)
Figure 8: )e 2-acetyl-1-pyrroline (2AP) contents of Khao Dawk Mali 105 (KDML105) grains grown under different cultivation systems.
)e error bars represent the standard deviation of measurements for nine soil samples. Note: ORF� organic rice farming; CRF� con-
ventional rice farming.
(1.00–1.50mg kg−1) [48]. However, another study showed and 2AP values compared to the values obtained from the
that KDML105 rice grains had a slightly higher 2AP content CRF system (Figures 10(a) and 10(b)). )e higher TN in the
when grown in clay loam (3.32mg kg−1) than in sandy loam ORF system (Figure 10(b)) may be one of the main causal
(2.87mg kg−1) [49]. In the present study, on average, finer agents of a much higher 2AP level in this system because
textured soils tended to increase the 2AP content of rice 2AP is an N-containing aromatic compound. Yang et al. [10]
grains more than coarser textured soils did (Figure 9). It is concluded that TN in the soil is one of the key factors in the
interesting to note that the farming practice exerted a aroma production of Chinese aromatic rice.
stronger influence on the 2AP content of the rice grains than )e higher HA content in the ORF systemmay have also
on the soil texture. Under the same soil texture, the 2AP level contributed to higher 2AP content in the rice grains than in
obtained from the ORF system was much higher than that the CRF system (Figure 10(c)). HA derived from organic
obtained from the CRF system (Figure 9). matter decomposition contains many types of N com-
Owing to the low natural fertility of the TKR soils that pounds, including polyamines. Although proline is known
exhibit high spatial variability, attempts have been made to as the precursor for the biosynthesis of 2AP [50], a study on
improve rice crop yield by various soil management the aromatic gene Os2AP in KDML rice seedlings indicated
methods. Chemical fertilizer addition in the TKR region has that 2AP is synthesized via the polyamine pathway [51].
not been very successful as this practice exerts a negative )erefore, we suggested that organic N, including poly-
effect on the aromatic content of KDML105 [49]. Recently, amines in HA, may also play an important role in 2AP
much attention has been paid to improving the TKR soil increments of the ORF system in TKR. Pearson correlation
fertility, rice yield, and quality with organic matter (OM) coefficients were calculated among the 2AP concentrations,
application. )e results of the present study indicated that soil properties, and microbial populations (Table 2). A
the organic fertilizer application in the ORF system not only significantly positive correlation at p< 0.01 was found be-
increased the SOM level but also resulted inmuch higher TN tween SOM (0.8858∗∗∗), HA (0.6881∗∗∗), and TN
Number of bacterial isolates (×106 cfu g–1)
Concentration of 2AP (mg kg–1)
Number of actinomycetal isolates (×105 cfu g–1)
Number of fungal isolates (×104 cfu g–1)
Applied and Environmental Soil Science 9
20
18
16
14
12
10
8
6
4
2
0 ORF CRF ORF CRF ORF CRF ORF CRF
Farming practices
Loamy sand Sandy loam Loam Silt loam
Soil texture
Figure 9: )e 2-acetyl-1-pyrroline (2AP) content in Khao Dawk Mali 105 (KDML105) grains as affected by soil texture groups. Note:
ORF� organic rice farming; CRF� conventional rice farming.
SOM (%) Total N (mgN/100 g–1)
10
9 10
8
7 8
6
5 6
4
3 4
2 2
1
0 ORF CRF 0 ORF CRF
SOM (%) Total N
2AP (mg kg–1) 2AP (mg kg–1)
(a) (b)
Humic acid (%) SOM (%)
16
10 14
9 12
8
7 10
6 8
5
4 6
3 4 R2 = 0.8858
2
1 2
0 ORF CRF 0
0.00 0.50 1.00 1.50 2.00 2.50 3.00
Humic acid (%) SOM (%)
2AP (mg kg–1)
(c) (d)
Figure 10: Continued.
Concentration of 2AP (mg kg–1)
2AP (mg kg–1)
10 Applied and Environmental Soil Science
Total N (%) Humic acid (%)
16 16
14 14
12 12
10 10
8 8
6 6
4 R2 = 0.8857 4
2
2 2 R  = 0.6881
0 0
0.00 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.00 0.50 1.00 1.50 2.00
Total N (%) Humic acid (%)
(e) (f )
Figure 10: )e amount of 2-acetyl-1-pyrroline (2AP) content in Khao Dawk Mali 105 (KDML105) rice grains as affected by soil organic
matter (SOM) (a), total nitrogen (TN) (b), and humic acid (HA) (c) and their relationship with 2AP (d e, f ). Note: ORF� organic rice
farming; CRF� conventional rice farming.
Table 2: Pearson’s correlation matrix for the 2-acetyl-1-pyrroline (2AP) concentrations, physicochemical properties, and soil microbial
populations.
p values 2AP pH OM Humic acid EC CEC Total N Bacteria Actinomycetes Fungi
r values
2AP
pH −0.4333
OM 0.8858∗∗∗ −0.2238
Humic acid 0.6881∗∗∗ −0.2612 0.5402∗∗
EC 0.5259∗∗∗ −0.234 0.3568 0.4115
CEC 0.1946 −0.6121 0.0652 0.0936 0.3822
Total N 0.8857∗∗∗ −0.2238 1 0.5402∗∗ 0.3568 0.0652
Bacteria 0.7646∗∗∗ −0.341 0.6269∗∗∗ 0.3964 0.5007∗∗ 0.2447 0.6269∗∗∗
Actinomycetes 0.8364∗∗∗ −0.2159 0.7768∗∗∗ 0.6595∗∗∗ 0.5958∗∗∗ 0.1334 0.7768∗∗∗ 0.4837
Fungi 0.7509∗∗∗ −0.3731 0.793∗∗∗ 0.5179∗∗ 0.5069∗∗∗ 0.0542 0.7930∗∗∗ 0.6334∗∗∗ 0.6518∗∗∗
∗∗, ∗∗∗significant correlational p< 0.05 and 0.01, respectively.
(0.8857∗∗∗) and the 2AP concentration (Table 2; 3.3. Principal Component Analysis for the 2AP Content
Figures 10(d)–10(f )). Concentrations and Soil Properties. PCA provides good in-
formation on the relationship among variables. )e rela-
tionship between the farming practices, soil properties, and
3.2.3. 2AP Affected by Soil Microbial Populations. )e or- rhizosphere microorganisms and the 2AP examined by PCA
ganic inputs in the ORF system in this study not only allowed us to characterize each horizon type (Figure 12).)e
increased the SOM, TN, and HA values but also the first two components explained 60.7% of the total variability;
microbial population of KDML105. )ese soil factors component 1 explained 35.1%, while component 2 explained
showed a high positive correlation with 2AP levels in 25.6%. Organic and conventional farming were identified on
KDML105 grains (Figures 10 and 11). A significantly the correlation circle. It appeared that most of the soil
positive correlation (p< 0.01) was found between the properties showed a positive relationship with the ORF
bacterial (0.7646∗∗∗), actinomycetal (0.8364∗∗∗), and system. )e results of the PCA clearly indicated that the
fungal (0.7509∗∗∗) populations and the 2AP concentration SOM, TN, HA, EC, bacterial, actinomycetal, and fungal
(Figure 11; Table 2). )ese results indicated the high values had the strongest correlation with 2AP in the rice
impact of rice rhizosphere microorganisms on the 2AP grains. A very close relationship was also found among
level in KDML 105 rice grains. It was reported that several SOM, TN, HA, and the microbial population. A very high
bacterial genera such as Bacillus, Acinetobacter, Pseudo- correlation between these soil factors and 2AP appeared to
monas, and Enterobacter increased the 2AP level of ar- contribute to the ORF practices and was explained by the
omatic rice by 1.14–1.42-fold [52]. )erefore, it could be fact that high SOM in the ORF soil is a source of N, carbon,
concluded from this study that the higher microbial and energy for microorganisms and that HA is synthesized
population in the ORF system might be one of the key by their activity (Figure 12). In addition, 2AP is an
factors in enhancing 2AP synthesis in the rice grains. N-containing volatile compound, and its synthesis can be
2AP (mg kg–1)
2AP (mg kg–1)
Applied and Environmental Soil Science 11
Bacteria
16
14
10 12
9 10
8
7 8
6 6
5
4 2AP 4
R2 = 0.7646
3 Fungi 2
2 Actinomycetes
1 0
0 Bacteria 0 10 20 30 40 50 60 70ORF CRF
Number of bacterial isolates (×106)
Bacteria Fungi
Actinomycetes 2AP
(a) (b)
Actinomycetes Fungi
16 16
14 14
12 12
10 10
8 8
6 R
2 = 0.7509
R2 = 0.8364 6
4 4
2 2
0 0
0 5 10 15 20 25 0 5 10 15 20
Number of actinomycetal isolates (×105) Number of fungal isolates (×104)
(c) (d)
Figure 11: Influence of soil microbial populations on the 2-acetyl-1-pyrroline (2AP) content in Khao Dawk Mali 105 (KDML105) rice
grains (a) and their relationship with the 2AP content (b), (c), and (d). Note: ORF� organic rice farming; CRF� conventional rice farming.
1
5
Clay CEC
Silt Ca Mg
8 S
18 17 2
K 916 10
0 ActinomycetesP Bacteria
14 5 EC Fungus
13 7 3 4 Humic acid 6 N
2AP
OM
11
12 pH 15
Sand
−5
−4 −2 0 2 4 6
Dim1 (35.1%)
Farming Contributions
Conventional 8
Organic 64
2
Figure 12: Principal component analysis for cultivation practices, soil properties, soil microbial population, and 2-acetyl-1-pyrroline (2AP).
2AP (mg kg–1)
Log cfu g–1
Dim2 (25.6%)
2AP (mg kg–1) 2AP (mg kg–1)
12 Applied and Environmental Soil Science
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