Search

The inductively coupled plasma (ICP)-based method provides the opportunity to determine phosphorus (P) along with other major, secondary, micro and trace elements in plant materials. This study was conducted to compare and evaluate the relative efficacy of the inductively coupled plasma-optical emission spectrometry (ICP-OES) method with that of the colorimetric method using Skalar autoanalyzer, for determining P in 428 grain samples of eight diverse crops. The results on grain P analysis by the two methods, for individual as well as for all crop samples combined, showed that they were highly positively correlated (r varied from 0.84 to 0.98, p

Drought stress invariably reduces yield and may alter seed chemistry. This experiment was initiated to characterize the sorghum [Sorghum bicolor (L.) Moench] mini core collection for genetic variation and to study the effect of postflowering drought on seed Fe and Zn concentrations. Accessions with similar maturity, together with controls, were evaluated in split-plot design under irrigated and drought-stressed environments for two postrainy seasons. Residual (or restricted) maximum likelihood (REML) analysis of data considering genotypes as random and drought and year as fixed indicated highly significant variance as a result of genotypes. Highly significant effects of drought (D), year (Y), and D x Y interaction emphasized need for multilocation evaluation of germplasm for agronomic and seed nutritional traits. About twofold variation in Fe (25.8–48.9 mg kg−1 seed) and threefold variation in Zn (13.5–42.6 mg kg−1 seed) concentrations was observed across environments. Eleven accessions with high seed Fe, 14 accessions with high Zn, and nine accessions high in both Fe and Zn were identified. These accessions, however, produced low seed yields. In addition, six and four accessions, respectively, showed 8 to 39% and 9 to 38% greater Fe and Zn over control IS 33844 and produced seed yields similar to that of IS 33844. Significant rank correlation (0.70) indicated that accessions with high Fe or Zn under irrigated environments are also expected to perform well under drought-stressed environments. Significantly positive correlation between Fe and Zn indicated simultaneous improvement as a realistic approach in breeding. The identified germplasm are ideal genetic resources for the development of Fe- and Zn-dense sorghum cultivars.

Iron (Fe) deficiency chlorosis in crops is common in high-pH calcareous soils. Soil and plant testing is routinely used for diagnosing iron (Fe) deficiency chlorosis in crops, with mixed results. This article presents an overview of the factors that influence soil and plant tissue testing results. It is clear that soil tests for Fe are dominantly influenced by soil pH, bicarbonate, and moisture regime rather soil test result per se. This is because the solubility of Fe is more regulated by soil pH and moisture regime. Plant tissue testing for Fe can complement the results of soil testing for Fe. But at times, especially in calcareous soils, total Fe in plant tissue is not related to Fe deficiency, but metabolically active Fe is better at diagnosing the occurrence of the disorder. A combined use of soil and plant tissue testing seems more helpful in diagnosing Fe deficiency chlorosis disorder in crops.

Submerging soil creates a series of changes that have important implications for fertility and its management in wetland rice. Wetland rice makes an important contribution to the global rice supply and is often cited as an example of a sustainable production system. We little realize that flooding soil is a powerful driver of changes in fertility and nutrient availability via two most important determinants of soil fertility—pH and redox potential (Eh). The fundamental role of pH in regulating the dynamics of major and micronutrients, toxins, and reduction products in soil solution is well known and used to optimize rice production through management; however, the role of Eh, although equally important, is not appreciated and hence not fully exploited in developing improved fertility management practices. From a synthesis of global literature, this article presents a conceptual framework for the dynamics of soil organic matter and plant nutrients in terms of the combined effects of pH and Eh in submerged ...

Nitrification, the biological oxidation of ammonium to nitrate, weakens the soil's ability to retain N and facilitates N-losses from production agriculture through nitrate-leaching and denitrification. This process has a profound influence on what form of mineral-N is absorbed, used by plants, and retained in the soil, or lost to the environment, which in turn affects N-cycling, N-use efficiency (NUE) and ecosystem health and services. As reactive-N is often the most limiting in natural ecosystems, plants have acquired a range of mechanisms that suppress soil-nitrifier activity to limit N-losses via N-leaching and denitrification. Plants' ability to produce and release nitrification inhibitors from roots and suppress soil-nitrifier activity is termed 'biological nitrification inhibition' (BNI). With recent developments in methodology for in-situ measurement of nitrification inhibition, it is now possible to characterize BNI function in plants. This review assesses the current status of our understanding of the production and release of biological nitrification inhibitors (BNIs) and their potential in improving NUE in agriculture. A suite of genetic, soil and environmental factors regulate BNI activity in plants. BNI-function can be genetically exploited to improve the BNI-capacity of major food- and feed-crops to develop next-generation production systems with reduced nitrification and N2O emission rates to benefit both agriculture and the environment. The feasibility of such an approach is discussed based on the progresses made.

A study was conducted for comparative evaluation of atomic absorption spectrophotometry (AAS) and inductively coupled plasma–optical emission spectroscopy (ICP-OES) for determining extractable zinc (Zn), copper (Cu), manganese (Mn), and iron (Fe) in sixty diverse soil samples having a wide range in pH and organic carbon (C). The results were significantly affected by the method of analysis and soil type but generally did not follow a definite trend. Results for extractable Fe in Alfisol samples were significantly greater when using ICP-OES than AAS; and the results for Zn, Cu, and Mn were not significantly different for the two methods. For Vertisol samples, the results for extractable Cu were significantly greater by ICP-OES than by AAS, whereas extractable Fe and Zn were significantly greater by AAS than by ICP-OES, and the results for Mn were not significantly different for the two methods. The results are discussed relative to soil type and differences in soil organic carbon and pH of the samples used...

Soil health assessment of farmers’ fields in watershed villages in Medak district, Andhra Pradesh, India showed widespread deficiencies of sulfur (S), boron (B), and zinc (Zn) in addition to organic carbon and phosphorus (P). Participatory on-farm trials on soil test-based application of deficient Zn, B, and S along with nitrogen (N) and P during 2009 to 2012 significantly increased crop yields over farmers’ practice (FP)—by 31% to 45% in chickpea, 15% to 16% in cotton, 12% to 15% in paddy, and 8% to 9% in sugarcane. Total soluble sugars in sugarcane under balanced nutrition (BN) increased by 13%. Residual benefits of S, B, and Zn were observed in succeeding chilly crop (12% higher yield). Benefit to cost (B:C) ratios of BN ranged between 2.8 to 8.5 in chickpea, 2.6 to 4.4 in cotton, 2.3 to 2.9 in paddy, and 7.1 to 11.4 in sugarcane, indicating economic feasibility for scaling-up.

Microbiota in the gut play essential roles in human health. Prebiotics are non-digestible complex carbohydrates that are fermented in the colon, yielding energy and short chain fatty acids, and selectively promote the growth of Bifidobacteria and Lactobacillae in the gastro-intestinal tract. Fructans and inulin are the best-characterized plant prebiotics. Many vegetable, root and tuber crops as well as some fruit crops are the best-known sources of prebiotic carbohydrates, while the prebiotic-rich grain crops include barley, chickpea, lentil, lupin, and wheat. Some prebiotic-rich crop germplasm have been reported in barley, chickpea, lentil, wheat, yacon, and Jerusalem artichoke. A few major quantitative trait loci and gene-based markers associated with high fructan are known in wheat. More targeted search in genebanks using reduced subsets (representing diversity in germplasm) is needed to identify accessions with prebiotic carbohydrates. Transgenic maize, potato and sugarcane with high fructan, with no adverse effects on plant development, have been bred, which suggests that it is feasible to introduce fructan biosynthesis pathways in crops to produce health-imparting prebiotics. Developing prebiotic-rich and super nutritious crops will alleviate the widespread malnutrition and promote human health. A paradigm shift in breeding program is needed to achieve this goal and to ensure that newly-bred crop cultivars are nutritious, safe and health promoting.

Diffuse reflectance spectroscopy (DRS) is a rapid and noninvasive assessment technique for several spectrally active soil properties (chromophores) such as sand, clay, organic C, and Fe contents. The approach is also used for estimating many spectrally inactive constituents (non-chromophores) based on the assumption of covariation between non-chromophores and chromophores. The linkage between covariation and the ability of DRS to estimate a non-chromophore has not been reported in the literature. In this study, we evaluated the covariation assumption using three dependency measures (Pearson correlation coefficient, r; biweight midcorrelation, bicor; and mutual information based adjacency, AMI), five chromophores (organic C, Fe, clay, and sand contents, and geometric mean diameter), and seven non-chromophores (pH, electrical conductivity, P, K, B, Zn, and Al contents) measured in 247 Alfisol and 249 Vertisol samples. An average dependency index (ADI) was developed for each of the three measures (ADIr, ADIbicor, and ADIAMI). The first derivative of the reflectance in conjunction with partial least squares regression was used for data modeling. Model accuracy was evaluated using residual prediction deviation (RPD). The relationships between RPD values of non-chromophores and the ADI values were examined for different chromophore groups (physical, chemical, and combined). The performance of ADIAMI was found to be superior to ADIr and ADIbicor. The ADIAMI computed using chemical chromophores gave strong linear relationships (R2 = 0.93) between ADIAMI and the RPD of chemical non-chromophores, suggesting that the AMI may be used as a robust dependency measure to assess the covariation of non-chromophores with chromophores in DRS.

With environmental issues relating to heavy-metal contamination of natural resources becoming of increasing concern, there is an obvious need to have a method that can be used for routine analysis of a range of materials including soil, sediment, sewage sludge, plant, mineral and organic fertilizers, and other miscellaneous materials for heavy metals of concern. A single-step microwave digestion method was developed using aqua regia solution for digestion of finely ground samples for determining 15 heavy metals in soil, plant, and fertilizer materials using inductively coupled plasma–optical emission spectrometry (ICP-OES). Results on the recoveries of 15 heavy metals added via certified standard reference sample to soil, plant, or fertilizer samples showed that the results varied with the metal and the substrate, and with few exceptions, the results were satisfactory. The method is simple, rapid, and accurate and seems ideal for the routine analyses of a range of materials. Using microwave-assisted diges...

In view of widespread deficiencies, a long-term experiment was started at the International Crops Research Institute for the Semi-Arid Tropics, Patancheru, India in 2007 to identify economically efficient application strategy (full or 50% dose every or every second year) of sulphur (S) (30 kg ha−1), boron (B) (0.5 kg ha−1) and zinc (Zn) (10 kg ha−1). During the fourth year in 2010, balanced fertilization through adding S, B and Zn increased maize grain yield by 13–52% and soybean yield by 16–28% compared to nitrogen (N) and phosphorus (P) fertilization alone. Balanced nutrition increased N and P uptake, utilization and use efficiency for grain yield and harvest index indicating improved grain nutritional quality. The N, P plus 50% of S, B and Zn application every year recorded highest crop yields and N and P efficiencies indices and increased rainwater use efficiency with a benefit:cost ratio of 11.9 for maize and 4.14 for soybean. This study showed the importance of a deficient secondary nutrient S and m...

Thirty-two diverse Jatropha curcas L. cultivars were analyzed for their oil content by the standard Soxhlet extraction method using hexane as solvent. The results were then compared with those obtained by nuclear magnetic resonance (NMR) spectrometer. The cultivars had a wide range in oil content, which ranged from 4.8 to 38.8% by the Soxhlet method and from 6.0 to 38.9% by the NMR method. The values of oil content determined by the NMR method were highly significantly correlated (R2 = 0.9929, P < 0.0001, n = 32) with those obtained using the Soxhlet method. The NMR method is simple, nondestructive, rapid, and accurate for the routine analysis of oil content in Jatropha.

Internal soil standards are used in an analytical laboratory as one of the tools for providing feedback on the quality of soil-testing service provided. The objective of this study is to provide results on the temporal variability in soil-test values of the internal soil standards used for soil organic carbon and extractable phosphorus (P), potassium, sulfur, boron, and zinc determination in our analytical service laboratory. The range, mean, standard deviation, and coefficient of variation values for the internal standards for various fertility parameters varied according to the parameter and were generally of acceptable quality, except for the extractable P (Olsen P) in the lower range of extractable P. Our results show that the use of internal soil standards in an analytical service laboratory is a simple, inexpensive, and effective tool for providing feedback on the quality of soil-testing service.

Analysis of soils from 421 farmers’ fields in eastern districts of Rajasthan, India, revealed widespread deficiencies of sulfur (S; 43 to 87% fields deficient), boron (B; 25 to 100%), and zinc (Zn; 0 to 94%) in addition to phosphorus (P; 10 to 73%) and soil organic carbon (1 to 84%). An integrated approach of application of deficient S, B, and Zn along with N and P to high-yielding crop cultivars increased yield over farmers’ practice of N and P application to local cultivars by 92 to 204% in maize, 115 to 167% in pearl millet, and 150% in groundnut. Benefit-to-cost ratio of the integrated strategy varied from 3.33 to 8.03 in maize, 2.92 to 3.40 in pearl millet, and 1.15 in groundnut. The integrated approach effectively utilized scarce water in food production and increased rainwater-use efficiency at 67 to 145 kg mm−1 ha−1 from 21 to 50 kg mm−1 ha−1 under farmers’ practice.

The chlorophyll meter (SPAD-502) is used to estimate nitrogen status of various crops. However, the relationship between SPAD readings and leaf nitrogen concentration (LNC) in sweet sorghum (Sorghum bicolor) has not been fully established. We examined the relationship between SPAD readings and LNC in sweet sorghum in a two-year study; and the effects of leaf thickness on the relationship was also examined. There was a significant relationship between the SPAD reading and LNC at each of two growth stages, but the correlation was weaker when the data for the two growth stages were pooled. This correlation improved when the specific leaf area was introduced as a second independent variable in the multiple regression analysis. This regression equation was applicable to not only different growth stages but also different seasons. The results suggest that the regression equation developed in this study can help in optimizing nitrogen fertilization for sweet sorghum production.

The knowledge on the relationships of protein and micronutrient concentration in wheat grain with edaphic characteristics could provide valuable information for site-specific fertilization of crops for producing grains denser in micronutrients such as iron (Fe) and zinc (Zn) in rain-fed agriculture. In this study, we used soil properties and topographic parameters in the artificial neural network (ANN) methodology as a power tool for improving models for predicting wheat grain micronutrient and protein contents in the hilly regions of western Iran. Soil and grain samples were collected from 1 m2 plots using the stratified random method, whereas the slope positions were considered as the basis of soil sampling, at 100 selected points. The mean grain Zn, Fe, Cu (copper) and Mn (manganese) concentrations were 37.02, 65.86, 14.79 and 44.93 mg–1 kg–1, respectively, and mean grain protein was 13.76%. Application of the ANN models for predicting Zn, Fe, Cu, Mn and protein contents in grains improved prediction b...

Heavy metals are governed by parent material of soils and influenced by the soil physicochemical properties and soil and crop management practices. This paper evaluates total heavy metal concentrations in rainfed soils under diverse management practices of tropical India. Vertisols (clayey soils with high shrink/swell capacity) had the highest concentrations of heavy metals. However, chromium (Cr) content was above the threshold value in Aridisol [calcium carbonate (CaCO3)]-containing soils of the arid environments with subsurface horizon development. Concentration increased at lower depths (>30 cm). Basaltic soils showed higher concentrations of nickel (Ni), copper (Cu) and manganese (Mn). Cadmium (Cd), cobalt (Co), Cu and Mn concentrations were higher in soils cultivated to cotton, whereas Cr concentration was above the threshold level of 110 mg kg−1 in food crop cultivated soils. As the specific soil surface is closely related to clay content and clay type, soil’s ability to retain heavy metals is more closely tied to the specific surface than to the soil cation exchange capacity. Higher positive correlations were found between heavy metal concentrations and clay content [Cd(r = 0.85; p ≤ 0.01); Co (r = 0.88; p ≤ 0.05); Ni (r = 0.87; p ≤ 0.01); Co (r = 0.81; p ≤ 0.05); Zn (r = 0.49; p ≤ 0.01); Cr (r = 0.80; p ≤ 0.05); Mn (r = 0.79; p ≤ 0.01)]. The amounts of nitrogen–phosphorus–potassium applied showed a positive correlation with Co and Ni (r = 0.62; p ≤ 0.05). As several soils used for growing food crops are high in Ni, Cr and Mn, the flow of these metals in soil–plant–livestock/human chain needs further attention.

The aim of this study was to understand the inheritance of grain iron (Fe) and zinc (Zn) concentrations in sorghum [Sorghum bicolor (L.) Moench] and to assess the possibility of exploiting heterosis to improve these micronutrients. Three sets of full diallel crosses were made, one set using five parents contrasting for both grain Fe and Zn concentrations; the second set using six parents contrasting only for Fe, and the third set with four parents contrasting only for Zn. The crosses and parents were evaluated in replicated trials for two years. The results indicated that both additive and non-additive gene action play a role in conditioning grain Fe and Zn concentration in sorghum. However, non-additive gene action is predominant in conditioning grain Fe; and additive gene action in conditioning grain Zn. Some of the crosses showed significant heterosis for grain Fe concentration without yield penalty and some crosses showed targeted grain Zn concentration (40 mg kg−1) coupled with higher grain yields. The results also showed that it is possible to improve grain Fe concentration through exploiting heterosis, but there would be little opportunity if any for improving grain Zn through heterosis breeding. To develop hybrids with high grain Fe and Zn concentration in sorghum both parents needs to be improved for these micronutrients. Combining higher grain Fe and Zn with high yield is feasible.

A study was made to determine the influence of pasture degradation on soil quality indicators that included physical, chemical, biological and micromorphological attributes, along the hillslope positions in Chaharmahal and Bakhtiari province, western Iran. Soil samples from different slope positions were collected from 0 to 30 cm depth for physical and chemical properties and from 0 to 15 cm depth for biological properties at two adjacent sites in the two ecosystems: natural pasture and cultivated land. Soil quality indicators including bulk density, mean weight diameter, soil organic carbon (SOC), particulate organic material (POM) in aggregate fractions, total nitrogen, available potassium, available phosphorus, cation exchange capacity, soil microbial respiration (SMR) and microbial biomass C and N were determined. The results showed that SOC decreased cultivation from 1.09 to 0.77 % following pasture degradation. The POM decreased by about 19.35 % in cultivated soils when compared to natural pasture; also, SMR and microbial biomass C and N decreased significantly following pasture degradation. Furthermore, aggregate stability and pore spaces decreased, and bulk density increased in the cultivated soils. Overall, our results showed that long-term cultivation following pasture degradation led to a decline in soil quality in all selected slope positions at the site studied in the semiarid region.

pearl millet ( Pennisetum glaucum (L.) r. Br.) is an important staple food crop in the semiarid tropical regions of Asia and Africa. As part of a major initiative to improve its grain Fe and Zn densities, two sets of line × tester studies were conducted. results showed that the underlying physiological processes determining the grain Fe and Zn densities were largely under additive genetic control, and Fe and Zn densities of the inbred lines per se and their general combining ability (GCA) were positively and highly signifi- cantly correlated. This would imply that recur - rent selection can be effectively used to improve the breeding populations for grain Fe and Zn densities and that breeding lines selected for high Fe and Zn densities per se are more likely to include those with high GCA for these micro - nutrients. Lack of better-parent heterosis indi - cated that to breed hybrids with high Fe and Zn densities would require high levels of these micronutrients in both parental lines. Highly sig - nificant and positive correlations between the Fe and Zn densities, between the GCA of Fe and Zn densities, and between the specific combining ability (SCA) of the Fe and Zn densities showed that simultaneous selection for both micronutri - ents is likely to be effective with respect to all these performance parameters. Consistency in the patterns of results across both sets of trials and across the environments for all the param - eters implies that these results could be of wider application to the genetic improvement of Fe and Zn densities in pearl millet.

The ability to suppress soil nitrification through the release of nitrification inhibitors from plant roots is termed ‘biological nitrification inhibition’ (BNI). Here, we aimed at the quantification and characterization of the BNI function in sorghum that includes inhibitor production, their chemical identity, functionality and factors regulating their release. Sorghum was grown in solution culture and root exudate was collected using aerated NH4Cl solutions. A bioluminescence assay using recombinant Nitrosomonas europaea was employed to determine the BNI activity. Activity-guided chromatographic fractionation was used to isolate biological nitrification inhibitors (BNIs). The chemical structure was analyzed using NMR and mass spectrometry; pH-stat systems were deployed to analyze the role of rhizosphere pH on BNIs release. Sorghum roots released two categories of BNIs: hydrophilic- and hydrophobic-BNIs. The release rates for hydrophilic- and hydrophobic- BNIs ranged from 10 to 25 ATU g−1 root dwt. d−1. Addition of hydrophilic BNIs (10 ATU g−1 soil) significantly inhibited soil nitrification (40 % inhibition) during a 30-d incubation test. Two BNI compounds isolated are: sakuranetin (ED80 0.6 μM; isolated from hydrophilic-BNIs fraction) and sorgoleone (ED80 13.0 μM; isolated from hydrophobic-BNIs fraction), which inhibited Nitrosomonas by blocking AMO and HAO enzymatic pathways. The BNIs release required the presence of NH 4 + in the root environment and the stimulatory effect of NH 4 + lasted 24 h. Unlike the hydrophobic-BNIs, the release of hydrophilic-BNIs declined at a rhizosphere pH >5.0; nearly 80 % of hydrophilic-BNI release was suppressed at pH ≥7.0. The released hydrophilic-BNIs were functionally stable within a pH range of 5.0 to 9.0. Sakuranetin showed a stronger inhibitory activity (ED50 0.2 μM) than methyl 3-(4-hydroxyphenyl) propionate (MHPP) (ED50 100 μM) (isolated from hydrophilic-BNIs fraction) in the in vitro culture-bioassay, but the activity was non-functional and ineffective in the soil-assay. There is an urgent need to identify sorghum genetic stocks with high potential to release functional-BNIs for suppressing nitrification and to improve nitrogen use efficiency in sorghum-based production systems.

Soil nutrient contents were determined in 802 surface soil samples (0–15 cm deep) collected from farmers' fields that support extensive cultivation of soybean (Glycine max L.) and finger millet (Eleusine coracana G.), spread across three districts, in the semi-arid regions of Karnataka, India. Following soil analysis, on-farm crop trials were conducted during 2005–2007 to study the crop response to the soil application of nitrogen (N), phosphorus (P), sulfur (S), boron (B), and zinc (Zn) fertilizers. Analyses of soil samples revealed that 4–83% fields were deficient in N, 34–65% in P, 83–93% in extractable S, 53–96% in B, and 34–88% of farmers' fields were deficient in Zn. On-farm trials conducted during the three rainy seasons (2005, 2006, and 2007) significantly (P ≤ 0.05) enhanced crop productivity indices such as yields of grain, stover, and total biomass in soybean and finger millet crops. Integrated management of deficient nutrients in finger millet and soybean crops significantly enhanced the grain...

Frequency of boron (B) deficiency is increasing in rainfed systems, and hence there is a need to diagnose the deficiency. Colorimetric methods are still widely used in soil-testing laboratories in India for measuring B. Little information is available on the comparative evaluation of the colorimetric and inductively coupled plasma (ICP) methods for determining extractable B in soils. We describe results of the comparative evaluation of these methods for measuring extractable B in 57 soil samples with pH values ranging from 5.3 to 9.5. There was a significant correlation between B values determined by the two methods, and the correlation coefficient was greater for soil samples with pH in the neutral to alkaline range. Interaction between soil samples and methods (ICP or colorimetric) was significant except for soil samples in the pH range of 8.0 to 9.5. Precision for B determination was greater with the ICP than with the colorimetric method.

In this study artificial neural network (ANN) models were designed to predict the biomass and grain yield of barley from soil properties; and the performance of ANN models was compared with earlier tested statistical models based on multivariate regression. Barley yield data and surface soil samples (0–30 cm depth) were collected from 1 m2 plots at 112 selected points in the arid region of northern Iran. ANN yield models gave higher coefficient of determination and lower root mean square error compared to the multivariate regression, indicating that ANN is a more powerful tool than multivariate regression. Sensitivity analysis showed that soil electrical conductivity, sodium absorption ratio, pH, total nitrogen, available phosphorus, and organic matter consistently influenced barley biomass and grain yield. A comparison of the two methods to identify the most important factors indicated that while in the ANN analysis, soil organic matter (SOM) was included among the most important factors; SOM was exclude...

In West Africa, two-thirds of upland rice is grown on acidic phosphorus (P)-deficient soils. Phosphorus is one of the most limiting-nutrients affecting crop productivity. A three-year field experiment was conducted on a Ferralsol in Cote d'Ivoire to study the response of four interspecific rice cultivars and a sativa (control cultivar) to Tilemsi phosphate rock (PR) and soluble triple superphosphate (TSP) fertilizer. PR was applied at 0, 150, 300, and 450 kg ha−1 P once in the first year and residual effects were measured in the following years. TSP (0, 50, 100 and 150 kg ha−1 P) was applied yearly. More significant yield increasing (38%) was observed in the second year. Annual application of 50 kg P ha−1 as TSP or a one-time application of 150 kg P ha−1 as PR was the optimum rate for the production of all cultivars. Higher rates of P from TSP (100 and 150 kg P ha−1) gave 2–3 times greater residual P in soil than the optimum rate, inducing no further response of rice. Two interspecific cultivars were iden...

Ammonium production in wetland soils and sediments is the key process that impacts nitrogen (N) availability, wetland productivity and environmental quality. Significant relationships between organic matter content and mineralizable N have been reported for diverse groups of wetland rice soils. However, recent research also showed that in soils under intensified wetland rice production systems, the relationships between organic matter and mineralizable N are poor or not significant. The review of recent research suggests that both organic matter quantity and quality are influenced by prolonged submergence, which in turn affects mineralization and N supply in wetland soils. While organic matter quantity increases following prolonged submergence of soil; submergence also changes the chemistry and quality of soil organic matter, which influences N mineralization. The increase in N mineralization as a result of increase in organic matter quantity is countered by the change in the chemistry and quality of organic matter. The changes in chemical composition of soil organic matter and their influence on N mineralization in submerged soils are discussed with examples from recent research.

Deficiency of sulfur (S) is becoming widespread in the rainfed systems of India, and there is increasing need for diagnosing the deficiency. Calcium chloride and Ca phosphate are commonly used for extracting available S in soils. Because of cost and the ease of availability locally, we prefer using Ca chloride as an extractant over Ca phosphate, for extracting available S. However, there is paucity of data on the comparative evaluation of the two extractants to extract available S, especially in soils having a wide range in natural pH (from acidic to alkaline range). It is recognized that soil pH plays a dominant role in the adsorption-desorption and extractability of sulfate-S in soils. We compared the extraction of S by Ca chloride and Ca phosphate in 86 Indian soils having a wide range in pH (4.5 to 10.6). Sulfur in the extracts was determined by ICP-AES. Considering all the 86 soil samples tested, there was an excellent agreement between the values of extractable S determined by using the two extractants (r=0.96, p

Experiments were conducted on-farm during two seasons (2003–2004) to determine the effects of sulfur (S), boron (B), and zinc (Zn) fertilization on the grain and straw quality of sorghum and maize grown under rainfed conditions in the semi-arid zone of India. The farmers' fields were deficient in S, B, and Zn; in addition the soils were low in organic matter and extractable phosphorus (P), but adequate in extractable potassium (K). Results showed that the applications of S, B, and Zn (SBZn) with nitrogen (N) and P (SBZn + NP) significantly increased the grain N, S, and Zn concentrations in maize and sorghum compared to farmer inputs (FI) and SBZn treatments; the results relative to P and B composition of the grain of the crops were not consistent and did not show any definite trend. The application of SBZn + NP over FI generally increased N, S, and Zn concentration in sorghum and maize straw compared to FI and SBZn treatments. The straw composition of the crops relative to P and B did not show a ...

Nitrification in soil converts relatively immobile ammonium-nitrogen (N) to highly mobile nitrate-N (via nitrite), and this has implications for N-use efficiency by agricultural systems as well as for environmental quality, especially in situations where the potential for loss of soil or added N is high following nitrate formation. The literature on various physical, environmental, and chemical factors and their interactions on nitrification in soil is reviewed and discussed with examples from natural and agro-ecosystems. Among the various factors, soil matrix, water status, aeration, temperature, and pH have strong influence on nitrification. The information on factors that influence nitrification is useful when developing strategies for regulating nitrification in soils by employing chemical or biological nitrification inhibitors.

On-farm studies were conducted during 2002–2004 to determine fertility status, including sulfur (S) and micronutrients, and crop response to fertilization on farmers' fields in the semi-arid zone of India. Nine hundred-twenty four soil samples taken from farmers' fields, spread in the three districts of Andhra Pradesh (India), were analyzed for soil chemical fertility parameters. Results showed that samples were low in organic carbon (C), total nitrogen (N), and low to moderate in extractable phosphorus (P), but adequate in available potassium (K). Analyses of soil samples for extractable S and micronutrients was most revealing and showed that 73–95% of the farmers' fields were deficient in S, 70–100% in boron (B), and 62–94% in zinc (Zn). On-farm trials conducted during three seasons (2002–2004) showed significant yield responses of maize, castor, groundnut, and mung bean to the applications of S, B, and Zn. The yield responses were larger when S, Zn, and B were applied along with N and P. Appli...

Application of legume green manure (GM) is suggested to be effective in increasing the availability of native soil phosphorus (P) and the dissolution and utilization of phosphate rock (PR)-P by food crops. Experiments were conducted to study the dynamics of extractable P (P extracted by Bray-1-extracting solution) of an Ultisol amended with or without GM residues of contrasting P concentrations in the absence of growing plants. In two separate experiments, GM residues of Aschynomene afraspera (a flood-tolerant legume) and of Crotalaria micans (upland) with varying P concentrations were added to an acidic soil amended with PR-P or triple superphosphate (TSP) in plastic bottles. Soil moisture was brought to field capacity of the soil in the upland experiment and saturated with distilled water in the lowland setup. This was done to simulate aerobic upland and anaerobic lowland soil conditions in the relevant plastic bottles. Only P concentration of the residues added varied, while lignin and C : N ratios were similar. A temperature of 25°C was maintained throughout the experiment. Changes in soil extractable Bray-1-P were measured at the end of the incubation period (60 or 80 d). In the aerobic soils, extractable P in the combined PR+GM or TSP+GM treatments was significantly lower than in the PR- or TSP- treated soils. The amendment with GM residues alone significantly increased Bray-1-P over the unamended control in the case of the inorganic P-fertilized GM residues. The trend in extractable P was similar in the soils incubated under anaerobic conditions. However, in the case of PR, concentrations of P extracted by Bray-1 solution did not significantly change in the presence or absence of GM. The results suggest that the incorporation of GM residues with low P concentration does not lead to a net P release in upland or lowland soils. These results have implications for nutrient cycling in farming systems in W Africa as most of the soils are poor and very low in available P.

Phosphorus deficiency has been identified as a major constraint to crop production on highly weathered, low activity clay soils in the humid and subhumid zones of sub-Saha-ran Africa. Phosphorus deficiency is further accentuated on many of the soils, especially Ul-tisols and Oxisols, because of fast reversion of soluble P into insoluble forms through reactions with iron and aluminum oxides. Phosphorus fertilization is of fundamental importance for sustaining crop production, maintaining soil fertility, and enhancing the fertility of degraded soils. Recent research indicates that the application of inorganic P through soluble and relatively reactive phosphate rock (PR) sources can be effective in increasing crop production and productivity, enhancing the replenishment of N through biological fixation, and in the maintenance of improvement of the overall fertility of soils. The effectiveness of PR and the residual value of fertilizer P from soluble and rock P sources can be enhanced by amending them with locally available organic and crop residues or by the recycling of P from rock RP through leguminous crops. It is suggested that an approach in which the use of P-efficient genotypes and P management are integrated is more practical and sustainable.

Soil nitrogen (N) supply plays a dominant role in the N nutrition of wetland rice. Organic matter has been proposed as an index of soil N availability to wetland rice. This is based on the finding that mineralizable N produced under waterlogged conditions is related to soil organic carbon (C) and total N. The relationship between organic matter and mineralizable N is a prerequisite for determining the N requirement of wetland rice. However, no critical analysis of recent literature on organic matter–mineralizable N relationships has been made. This article evaluates current literature on the relationships of mineralizable N or ammonium N production with soil organic C in wetland rice soils. A number of studies with diverse wetland rice soils demonstrate a close relationship of N mineralized (ammonium‐N) under anaerobic conditions with organic C or total N. However, a few recent studies made on sites under long‐term intensive wetland rice cropping showed that strong positive relationships of miner...

Experiments were conducted during 1996–1998 in screen house and in the field in the humid forest zone of Cote d’Ivoire, to evaluate the effects of phosphorus (P) from phosphate rock (PR) on the performance of the root nodulating legume Crotalaria micans grown for 8 weeks. The experimental soils were acid Ultisols with

Submerged soils differ considerably from their arable counterparts. Lack of oxygen and the reduced state of submerged soils cause this. Submerging a soil under water triggers a series of physical, chemical and biological changes that greatly affect the dynamics of soil fertility and its use for growing crops such as wetland rice. Due to lack of oxygen, the nitrogen (N) mineralization process in submerged soils stops at ammonium production and nitrification is at low ebb. Most rice soils, especially those in the tropics are rich in iron (Fe). Redox cycling of Fe exerts a wide-ranging influence on the biogeochemistry of submerged rice soils and aquatic sediments where Fe is abundant. This article critically assesses the literature on the role of reducible Fe, which participates in redox reactions in submerged

Wetland rice fields are source of atmospheric methane. Methane is formed following reduction of carbon dioxide by hydrogen and through decarboxylation of acetate in anaerobic soils under reduced conditions. Methane production requires flow of carbon and electrons to microbial population of methanogens under reduced conditions in the strict absence of free oxygen. Application of or in-situ availability of terminal electron acceptors (oxidants) such as ferric iron or sulfate allows iron or sulfate reducers to successfully compete for substrates, hydrogen or acetate, with methanogens. This stops methane production. Electron acceptors also oxidize methane and reduce its emission. Since iron redox system plays a dominant role in tropical rice soils, which are rich in iron, the role of iron oxides and hydroxides as electron acceptor for controlling methane emission from wetland rice fields deserves more attention. For mitigating methane emission from wetland rice fields, ferric iron as a terminal electron-accepting agent, can either be added to the soil or regenerated in the soil by manipulating redox potential through soil and water management. Examples are given from recent literature illustrating the role of electron acceptors (ferric iron, sulfate, etc.) in reducing methane emission from submerged rice soils. The need for future research is also examined.

Rice (Oryza sativa L.) demand in West Africa is unmet because of insufficient production. Legume fixed N [biological N fixation (BNF)] may sustainably increase rice productivity in low-input systems. However, P deficiency limits BNF on the acid soils encountered in the region, despite the prevalence of phosphate rock (PR). Pot and field experiments were conducted in Cote d'Ivoire in 1996–1998 to study the impact of combined legume and PR on rice performance. Triple superphosphate and PR were applied at rates of 60 (pot) and at 90 (field) kg P ha−1 to rice and the legume Aeschynomene afraspera grown for 8 wk and then incorporated before rice transplanting. Legume fixed N was determined by 15N isotope dilution. Under field conditions, addition of PR doubled the biomass of A. afraspera Irrespective of P source, P application increased the amount of BNF-N (three- to eightfold) to 36 mg N plant−l in pots and to 84 kg N ha−1 in the field. Nitrogen derived from the air was correlated with legume P uptake (r = 0.97***, where *** = significant at the 0.001 level) and nodulation (r = 0.91**, where ** = significant at the 0.01 level). The synergy of PR and BNF on N and P cycling improved P nutrition and total biomass of subsequent lowland rice under pot conditions. Combining legume green manure (GM) with PR enhanced soil extractable Bray-1 P and may thus play an important role in improving the availability of PR. Under field conditions, due to asynchrony in GM nutrient release and demand, the impact of the combined GM–PR treatment on rice yield was minimal.

At the ICRISAT soil chemistry laboratory, a sulfuric acid–selenium (Se) digestion method has been used for several years for determination of nitrogen (N) and phosphorus (P) in a single plant digest. The method is simple and was evaluated for determining N, P, potassium (K), Calcium (Ca), and magnesium (Mg) in plant samples using a single digest. Finely ground plant materials of pigeonpea (Cajanus cajan L.) and rice (Oryza sativa L.) plant samples were digested at 370°C. Digestion completed in about 2.5 h when the digests were clear and colorless. Results with plant samples having a wide range in elemental concentrations, showed that there was an excellent agreement in the values of various elements determined by the proposed digestion procedure and the routinely used Kjeldahl and triacid acid digestion methods. These results suggest that sulfuric acid–Se mixture can be used for preparing plant digests for determination of N, P, K, Ca, and Mg in a single digest. In addition, this method is adapted for pre...

Dry ashing and wet ashing techniques are routinely used for preparing plant materials for elemental analysis. The two techniques generally give similar results for the analysis of plant materials but differences have been observed in results using the two methods for elements such as calcium (Ca), iron (Fe), and zinc (Zn). We made a study to compare the dry ashing and triacid digestion procedures for determining potassium (K), Ca, magnesium (Mg), Fe, manganese (Mn), copper (Cu), and Zn in sorghum and rice plant samples having a range in concentration of these elements. For sorghum, the two procedures gave similar results for the determination of K, Mg, Mn, and Zn, the dry ashing procedure gave higher values for Ca, Fe, and Cu than those obtained using the triacid digestion procedure. For rice, the two procedures gave similar results for all nutrient elements except Ca for which the values were higher by the dry ashing procedure than with the triacid digestion procedure. Our results suggest that dry ashing...

Modified version of a dichromate digestion procedure, earlier found suitable for simultaneous determination of organic carbon (C) and potentially mineralizable nitrogen (N) in soils, was evaluated for total N determination in 44 diverse soil samples from the semi‐arid region of India. The soils belonged to Vertisols and Alfisols and had a wide range in total N contents. The method involves digestion of the soil sample with an acidified dichromate solution for 30 minutes in a digestion tube in a block digester preheated to 165°C followed by determination of N in the digest by steam distillation procedure. The efficacy of the dichromate procedure for determining total N differed for the two soil types. Excellent correlations were observed between the values of total N obtained by the dichromate procedure (Dichro‐N) and by Kjeldahl method (Kjeldahl‐N) for Vertisols (R2=0.995; n=21) and Alfisols (R2=0.952; n=23). The regression equations describing the relationships between the two soil types can be ...

Assessing the fertilizer phosphorus (P) requirements (FPR) of crops is an important component of research for efficient and rational use of fertilizers. Soil and plant tests are employed to determine the FPR. Two methods were evaluated for determining the FPR of sorghum grown on a Vertisol under rainfed conditions. The first method was based on P on applied P uptake, and grain yield relationships for grain sorghum. In this method, P uptake at a given yield was determined from the relationship between total P uptake and grain yield. The amount of fertilizer P applied for the given P uptake and grain yield was then, determined from the relationship between P applied and P uptake. In the second method, FPR was determined using the equation: FPR=(Up‐U0)/PRF, where Up is P uptake at a given yield, U0 is P uptake from unfertilized soil, and PRF is the recovery of applied P. The parameters, U0, Up, and PRF were determined in a field experiment with sorghum grown on a Vertisol under rainfed conditions. T...

The effects of nitrogen (N) and/or phosphorus (P) fertilizers on the nutritional status in the rhizosphere were studied by monitoring throughout the growth period the concentrations of organic carbon (C), inorganic N, NaHCO3 extractable P, exchangeable K, Ca, and Mg in sorghum (Sorghum bicolor L. Moench) down in an Alfisol field, and of all these elements except for extractable P, and exchangeable Ca in a Vertisol field in semi-arid tropical India. These concentrations were compared between the rhizosphere soil and bulk soil of sorghum grown in both fields. Organic C content of the rhizosphere soil increased with plant age and was significantly higher than that in the bulk soil throughout the growth of sorghum, but it was not affected by the rates of N or P fertilizer. Inorganic N concentration in the rhizosphere soil was significantly higher than that in the bulk soil until maturity in sorghum. The content of available P in the rhizosphere soil was significantly higher than in the bulk soil afte...

Relatively little is known about the fixed NH4N status of soils in the semi-arid tropics (SAT) but information is needed in view of its role in N cycling and the N economy of the soils. The distribution of fixed NH4N and C/N ratios of soil profiles from two benchmark Vertisols and one Alfisol in the Indian SAT were studied. From 15.9 to 58.6% of the total soil N was present as fixed NH4N in the Vertisol profiles; the range was from 13.3 to 30.8% in the Alfisol profile and a higher percentage of fixed NH4N was found in the lower horizons. A method based on the extraction of soil samples with dilute HF solution was found suitable for determining fixed NH4N in these soils as the values of fixed NH4N determined by this method were in good agreement with those determined using the standard method. Organic C/total N ratios varied from 7.7 to 12.8 in the three profiles while the organic C/organic N ratios varied from 9.4 to 21.4. The results of this study emphasize the importance of fixed NH4N in assessing the N-status of the soils.

Little attention has been devoted to calibrating the soil tests for P in the field for crops grown under rainfed conditions in different soil types. Field experiments were conducted during the 1990 rainy season (June-September) at the ICRISAT Center, Patancheru (near Hyderabad), India on nearby Vertisol and Alfisol sites having a range in extractable P, for establishing relationships between extractable P and sorghum yield.

The response of crops to added P in Vertisols is generally less predictable than in other soil types under similar agroclimatic conditions. Very few studies have considered the residual effects of P while studying responses to fresh P applications. Field experiments were conducted for three years to study the response of sorghum to fertilizer P applied at 0, 10, 20 and 40 kg P ha−1, and its residual value in a Vertisol, very low in extractable P (0.4 mg P kg−1 soil), at the ICRISAT Center, Patancheru (near Hyderbad), India. In order to compare the response to fresh and residual P directly in each season, a split-plot design was adopted. One crop of sorghum (cv CSH6) was grown each year during the rainy season (June-September). The phenology of the sorghum crop and its harvest index were greatly affected by P application. The days to 50% flowering and physiological maturity were significantly reduced by P application as well as by the residues of fertilizer P applied in the previous season. In the first year of the experiment, sorghum grain yield increased from 0.14 t (no P added) to 3.48 t ha−1 with P added at the rate of 40 kg P ha−1. Phosphorus applied in the previous year was 58% as effective as fresh P but P applied two years earlier was only 18% as effective as fresh P.

Crop biofortification is a sustainable and cost-effective strategy to address malnutrition in developing countries. This review synthesizes the progress toward developing seed micronutrient-dense cereals and legumes cultivars by exploiting natural genetic variation using conventional breeding and/or transgenic technology, and discusses the associated issues to strengthen crop biofortification research and development. Some major QTL for seed iron and zinc, seed phosphorus, and seed phytate in common bean, rice,J;md wheat have been mapped. An iron reductase QTL associated with seed-iron ~QTL is found in common bean where the genes coding for candidate enzymes involved in phytic acid synthesis have also been mapped. Candidate genes for Ipa co segregate with mutant phenotypes identified in rice and soybean. The Gpe-B1 locus in wild emmer wheat accelerates senescence and increases nutrient remobilization from leaves to developing seeds, and another gene named TtNAM-B1 affecting these traits has been cloned. Seed iron-dense common bean and rice in Latin America; seed iron-dense common bean in eastern and southern Africa;.....

Nitrous oxide (N(2)O) emissions from Vertisols and Alfisols during sweet sorghum cultivation in the Indian semi-arid tropics were determined using a closed chamber technique during the rainy season (June-October) of 2010. The study included two treatments, nitrogen (N) at a rate of 90 kg/ha and a control without N fertilizer application. The N(2)O emissions strongly coincided with N fertilization and rainfall events. The cumulative N(2)O-N emission from Alfisols was 1.81 N(2)O-N kg/ha for 90 N treatment and 0.15 N(2)O-N kg/ha for the 0 N treatment. Similarly, the N(2)O-N emission from Vertisols was 0.70 N(2)O-N kg/ha for 90 N treatment and 0.09 N(2)O-N kg/ha for the 0 N treatment. The mean N(2)O-N emission factor for fertilizer induced emissions from the Alfisols was 0.90% as compared to 0.32% for Vertisols. Our results suggest that the N(2)O emissions are dependent on the soil properties. Therefore, the monitoring of N(2)O emissions from different agro-ecological regions, having different soil types, rainfall characteristics, cropping systems and crop management practices are necessary to develop comprehensive and accurate green house gas inventories.

Six field trials were conducted during the rainy seasons in 1987 and 1988 and dry season of 1988 at ICRISAT Sahelian Center, Niger, to investigate the effects of soil applied nematicides, inorganic fertilizers and farm yard manure (FYM) on spacial variability of groundnut growth and yield. Soil samples from the rhizosphere and geocarposphere zones of the stunted plants showed high numbers of plant-parasitic nematodes (Scutellonema clathricaudatum, Telotylenchus indicus andXiphinema parasetariae). Carbofuran alone at a rate of 10 kg a.i. ha-1 or in combination with FYM greatly reduced the population densities of plant-parasitic nematodes in the soil and roots as well as increased pod and haulm yields. Dibromochloropropane (DBCP) was most effective in reducing the variation in crop growth and significantly increased pod and haulm yields. No significant difference in crop growth, haulm and pod yields was observed between solarized and non-solarized plots.

Diffuse reflectance spectroscopy (DRS) operating in wavelength range of 350-2500 nm is emerging as a rapid and non-invasive approach for estimating soil nutrient content. The success of the DRS approach relies on the ability of the data mining algorithms to extract appropriate spectral features while accounting for non-linearity and complexity of the reflectance spectra. There is no comparative assessment of spectral algorithms for estimating nutrient content of Indian soils. We compare the performance of partialleast- squares regression (PLSR), support vector regression (SVR), discrete wavelet transformation (DWT) and their combinations (DWT-PLSR and DWT-SVR) to estimate soil nutrient content. The DRS models were generated for extractable phosphorus (P), potassium (K), sulphur (S), boron (B), zinc (Zn), iron (Fe) and aluminium (Al) content in Vertisols and Alfisols and were compared using residual prediction deviation (RPD) of validation dataset. The best DRS models yielded accurate predictions for P (RPD = 2.27), Fe (RPD = 2.91) in Vertisols and Fe (RPD = 2.43) in Alfisols, while B (RPD = 1.63), Zn (RPD = 1.49) in Vertisols and K (RPD = 1.89), Zn (RPD = 1.41) in Alfisols were predicted with moderate accuracy. The DWT-SVR outperformed all other approaches in case of P, K and Fe in Vertisols and P, K and Zn in Alfisols; whereas, the PLSR approach was better for B, Zn and Al in Vertisols and B, Fe and Al in Alfisols. The DWT-SVR approach yielded parsimonious DRS models with similar or better prediction accuracy than PLSR approach. Hence, the DWT-SVR may be considered as a suitable data mining approach for estimating soil nutrients in Alfisols and Vertisols of India.

The decomposition and accumulation of organic materials in submerged (anaerobic) soils and sediments differ considerably from those in their aerobic counterparts. This is caused by the lack of oxygen or anaerobiosis. Compared to aerobic soils, there is preferential accumulation of organic matter in submerged rice soils. This paper reviews the current literature to establish basis or bases for organic matter accumulation in wetland soils and sediments. The decomposition or destruction of organic materials is lessened and incomplete, and the humification of organic matter is decreased under flooded conditions. Consequently, the overall organic matter decomposition rates are slower in submerged soils than those in aerobic soils and this results in net accumulation of organic matter in soils or sites that remain flooded for several years. Also, high organic matter soils or Histosols are developed in permanently waterlogged sites or soils because the rate of organic matter destruction is slower than its accumulation. The balance between organic matter inputs and decomposition is the primary determinant of organic matter accumulation or depletion. Several hypotheses have been postulated to explain the accumulation of organic matter in submerged soils. They include the deleterious effects on microbial activity of reduction products produced such as hydrogen sulfide or volatile fatty acids and toxic concentrations of ammonia, aluminum, iron, and other cations in soil solution. The absence of electron acceptors such as iron oxides and hydroxides in submerged soils and sediments slows down organic matter oxidation and mineralization. Formation of recalcitrant complex organic molecules with organic matter fractions, e.g., through enrichment of organic matter with phenolics in intensified irrigated rice production system, may render them less available for microbial attack and utilization. Moreover, the net primary productivity of wetlands is higher than other ecosystems. There is need for further research to fully understand the mechanism(s) involved in the accumulation of organic matter in submerged soils as wetlands offer an excellent example of conservation and maintenance of organic matter and storage of organic C.