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A field study with varying nitrogen (N) rates (0-150 kg N ha-1) was conducted in Ludhiana (Punjab, India) in a randomized complete block design in three consecutive baby corn seasons to quantify and mitigate N losses to the environment. The nitrous oxide (N2O) flux emissions were measured at 2, 4, 8, 16, and 24 days after each fertilizer N split application. The leachate N losses were estimated by analyzing ammonium and nitrate ion content. Fertilizer N surplus to crop requirement explained 94.1% (spring), 95.9% (summer), and 95.5% (winter) variation in the area-scaled N losses (N2O, leachate). Lower fertilizer N usage by plants at early growth stages (upto V6 stage) resulted in higher N losses within ten days after the first fertilizer application. Carbon equivalent emissions followed the trend summer> spring>winter. Temporal variations during the monitoring seasons influenced the cob and stover yield in response to fertilizer N. On average, 67.9% of the applied fertilizer N was taken up by plants, 4.7% was lost via N leaching, 2.7% escaped as N2O, 3.2% accumulated in the soil profile, and 21.5% remained unaccounted. Sensing-based N application significantly improved N recovery efficiency by 51.2%, mitigated N emissions by 45.4%, and N leaching by 69.3% in comparison with fixed-time blanket fertilizer N topdressings. Fertilizer N management using PAU-LCC provided an economical and farmer-friendly solution to achieve a significant reduction in N losses while sustaining productivity. Further validation and transfer of technology to on-farm locations are needed to benefit from this work. [ABSTRACT FROM AUTHOR]

Fertilizer nitrogen (N) management in long-grained aromatic basmati rice (Oryza sativa) is critical because both below and above the optimum N application rate adversely affects yield. Multi-location field studies were conducted in northwestern India to formulate a site-specific N management (SSNM) strategy for basmati rice by monitoring the greenness of the fully expanded top leaf of the crop plants using a leaf color chart (PAU-LCC) specially developed at Punjab Agricultural University, Ludhiana. The green colour intensity of the successive panels of PAU-LCC increases with consistent decrease in optical reflectance by 1.6% (at 550 nm wavelength) and thus provides better precision in quantifying leaf colour greenness over the IRRI-LCC (the LCC developed at International Rice Research Institute, Philippines). The threshold leaf greenness at which a variety will respond to fertilizer N was found to be equal to LCC shade 3.5 and 4.0 for less and high N responsive varieties, respectively. Monitoring leaf greenness using LCC at weekly intervals and application of 10 kg N ha−1 whenever leaf greenness was less than the specified threshold level constituted the appropriate SSNM strategy. The SSNM produced grain yield equivalent to soil-test-based fixed N rates but with 20 to 60% less N fertilizer. Significantly higher agronomic (average 40.8 vs. 24.5 kg grain kg−1 N) and recovery (average 76.1 vs. 52.7%) efficiencies of fertilizer N were recorded with SSNM than with soil-test-based fixed fertilizer N rates. The SSNM also reduced N2O and GHG emissions by 20.1 and 23.6% as compared to soil-test-based fertilizer N rates. [ABSTRACT FROM AUTHOR]

Site-specific fertilizer nitrogen (N) management using chlorophyll meter (SPAD meter) can help drawing in-season need-based N topdressing decisions. However, SPAD meter based threshold chlorophyll value to trigger supplement N in spring maize is indistinct. Field studies were conducted for two years in sub-tropical and sub-humid climate to study variations in spectral properties and to establish threshold SPAD value for need-based N management in spring maize cultivars. Results specified that N concentration of topmost fully expanded leaf was closely correlated with SPAD meter readings from six-leaf stage (V6) to tasseling stages (VT). The Cate-Nelson plot expressed SPAD 50 as the threshold value to determine plant N need at different growth stages. Need-based topdressings of 30 kg N ha−1, whenever SPAD reading fell below the threshold 50 improved grain yield production by 7.6 to 10.2 per cent over soil test-based N application. SPAD threshold 45 guided N management was inadequate to meet plant N demand, whereas SPAD threshold 55 guided N application lead to N doses in excess of crop requirement without yield benefits. SPAD threshold 50 guided N management ensured better demand-supply synchrony throughout the growth stages and thus reported better N recovery and agronomic efficiencies over soil test-based N management. [ABSTRACT FROM AUTHOR]

Canopy reflectance measurements using active optical sensors have emerged as potential solution to draw in-season nitrogen (N) topdressings in cereals. Site-specific need-based N management strategy using a GreenSeeker optical sensor was developed and evaluated in spring maize. Four field experiments were conducted at two locations during 2017 and 2018 to develop an algorithm, and two experiments during 2019 to validate the sensor-based application for improving N use efficiency (NUE) and grain yield. The sensor measurements made at V9 growth stage with R2 value of 0.61 obtained from the relation between in-season estimate of yield (INSEY) and grain yield rendered better corrective N rate for improving NUE and getting optimum grain yield, whereas sensor measurements at V6, V12 and VT growth stages were not reliable for the purpose. Applying N rate in two splits of 30 kg N ha−1 at planting and 45 kg N ha−1 at V6 growth stage was recommended before applying sensor based corrective N rate at V9 stage. Sensor guided N topdressing produced yields similar to those obtained by following the soil test-based N recommendations but with lower N rates. These results were also reflected in considerable increase in N recovery (8 _18%) and agronomic (4 _13.5 kg grain kg−1 N) efficiencies in comparison with soil test-based N recommendations, thereby signifying the usefulness of the sensor-based algorithm in optimizing need-based fertilizer N management in spring maize. [ABSTRACT FROM AUTHOR]

The present study was conducted to establish prediction models for grain yield and nitrogen (N) uptake using normalized difference vegetation index (NDVI) measurements with the GreenSeeker optical sensor for different cultivar groups of basmati rice (Oryza sativa L.) and to define the optimum sensing timing. Sensor readings were collected at 21, 28, 35, 42, and 49 days after transplanting (DAT) from multi-cultivar and multi-rate N fertilization experiments conducted in 2016 and 2017. Prediction model established by regressing NDVI day−1 as the determinant of plant biomass with grain yield and N uptake at maturity following exponential functions revealed that sensing the crop before or after 35 DAT (panicle initiation stage) was not accurate and did not predict satisfactorily the yield or N uptake potential. Regression analysis generated two potential and viable yield or N uptake prediction models: one for the basmati rice cultivar CSR30 (tall cultivar), and the other for a PB-PUSA (group of semi-dwarf cultivars). Validation of the prediction models using an independent experiment conducted in 2018 revealed that sensing the crop at the panicle initiation stage provide grain yield and N uptake predictions close to the observed grain yield (R2 = 0.86, RMSE = 6.1%) and N uptake (R2 = 0.75, RMSE = 8.5%). This study showed that yield and N uptake potential in basmati rice can be predicted using in-season NDVI data measured with the GreenSeeker optical sensor. [ABSTRACT FROM AUTHOR]

A 4 years field study was conducted to improve nitrogen (N) and phosphorus (P) use efficiencies in wheat (Triticum aestivum L.) using arbuscular mycorrhizal fungi (AMF) and precision N management. Split plot design was employed to rationalize N and P fertilizer use in two different experiments with AMF in the main plot and fertilizer application practice in the subplots. The AMF seed coating improved mycorrhization, root dry weight and P uptake. AMF coating of wheat seeds improved mean grain yield and agronomic efficiency of applied P fertilizer (AEP) by 11% and 55.4%, respectively. However, AMF seed coating did not improve chlorophyll content, normalized difference vegetative index, grain yield and agronomic efficiency of applied N fertilizer (AEN). Precision N management using leaf color chart (LCC), chlorophyll meter (SPAD), and GreenSeeker optical sensor (GS) sustained wheat grain yield equivalent to the soil-test based N fertilizer recommendation with 20–31 kg ha−1 less fertilizer N. Proximal sensing guided N use improved AEN by 21.9%–39.6% while mitigating global warming potential by 16%–24%. Integrated use of AMF seed coating and precision N management provides a potential solution to improve N and P nutrition and reduce environmental footprints of fertilizer N use in wheat. [ABSTRACT FROM AUTHOR]

Nitrogen is one of the most important macronutrients for crop growth and metabolism. To identify marker-trait associations for complex nitrogen use efficiency (NUE)-related agronomic traits, field experiments were conducted on nested synthetic wheat introgression libraries at three nitrogen input levels across two seasons. The introgression libraries were genotyped using the 35K Axiom® Wheat Breeder's Array and genetic diversity and population structure were examined. Significant phenotypic variation was observed across genotypes, treatments, and their interactions across seasons for all the 22 traits measured. Significant positive correlations were observed among grain yield and yield-attributing traits and root traits. Across seasons, a total of 233 marker-trait associations (MTAs) associated with fifteen traits of interest at different levels of nitrogen (N0, N60, and N120) were detected using 9,474 genome-wide single nucleotide polymorphism (SNP) markers. Of these, 45 MTAs for 10 traits in the N0 treatment, 100 MTAs for 11 traits in the N60 treatment, and 88 MTAs for 11 traits in the N120 treatment were detected. We identified putative candidate genes underlying the significant MTAs which were associated directly or indirectly with various biological processes, cellular component organization, and molecular functions involving improved plant growth and grain yield. In addition, the top 10 lines based on N response and grain yield across seasons and treatments were identified. The identification and introgression of superior alleles/donors improving the NUE while maintaining grain yield may open new avenues in designing next generation nitrogen-efficient high-yielding wheat varieties. [ABSTRACT FROM AUTHOR]

In-situ field studies were conducted for three consecutive baby corn (Zea mays L.) growing seasons to quantify the amount of reactive N flowing beyond the rhizosphere while defining mitigation strategies. The N applications based on plant need were agronomically more efficient than the fixed-time blanket N applications. Average area-scaled leachate N losses in the winter season were 24 and 8% higher than the summer and spring seasons, respectively. A smaller root system at low N rate likely restricts plant N uptake and accelerates the magnitude of N leaching factor ranging from 6 to 9% in different seasons. Leachate N-flux peaks were more pronounced at early growth stages, attributed to the N supply in excess of the plant need. Residual soil mineral N varied little despite a wide range of fertilizer N rates, hence there was no evidence to support the idea that soils should be replenished for N removal by crops at fixed growth stages. Rather, N losses to the environment were greater using fixed-timing blanket N applications, which can be mitigated by a shift to N fertilization based on assessment of plant need. Use of the PAU-leaf colour chart and chlorophyll meter to guide need-based fertilizer N topdressings reduced average leachate NO3¯-N load by 69% over blanket N use practice, while producing an average 17% higher cob yield in baby corn. Hence, the blanket N use practices should be replaced with need-based N management strategies to mitigate environmental footprints of N use in the baby corn based cropping system. [ABSTRACT FROM AUTHOR]

Background: Excessive application of nitrogen (N) fertilizer in cereal crops not only decreases the N use efficiency but also accelerates greenhouse gas (GHG) emission. Aim: To improve N use efficiency in wheat (Triticum aestivum L.) using precision N management and coating seeds with arbuscular mycorrhizal fungi (AMF). Methods: Field experiment laid out in split‐plot design was conducted to study the role of AMF consortia (four species) seed coating and different precision N management strategies in rationalizing fertilizer N use. Results: The AMF seed coating improved mycorrhization but did not improve N assimilation, grain yield, root weight, N uptake, chlorophyll value, normalized difference vegetative index, and physiological efficiency (PEN) of applied N fertilizer. The benefits of AMF seed coating in improving N assimilation were not visible even in no‐N treatment. Precision N management using leaf color chart (LCC), chlorophyll meter (SPAD), and GreenSeeker optical sensor (GS) sustained wheat grain yield equivalent to the soil‐test based N fertilizer recommendation with the average savings of 20% N fertilizer. Precision N management strategies improved mean recovery efficiency (REN) and partial factor productivity (PFPN) of applied N fertilizer, respectively by 26.0% and 26.4% over the soil‐test based N management. Spectral properties measured with LCC, SPAD and GS showed good correlation (R2 > 0.71) with grain yield, depicting great potential of optical sensing tools in predicting grain yield and inferring need‐based fertilizer N topdressings decisions in wheat. Conclusions: Precision N management provides a potential solution to improve N nutrition in wheat while reducing nitrous oxide (N2O) and total GHG emissions by 23.2 and 23.6%, respectively, in comparison to soil‐test based N application. [ABSTRACT FROM AUTHOR]

Three-year multi-location field experiments were conducted in soils of varying inherent nitrogen (N) supply in diverse agro-climatic zones for improving productivity and mitigating N2O emissions in timely sown and late sown wheat. The biomass, total N uptake (TNU) and spectral properties were monitored at different growth stages. Biomass production and TNU statistics of only 0.76% and 3.4%, respectively, till Zadoks 14 growth stage (four leaves stage) revealed that applying all fertilizer N dose by Zadoks 14 is not an appropriate strategy to assure fertilizer N supply throughout the growth stages. Rescheduled fertilizer N topdressings with moderate N (25 kg ha−1) at sowing and remaining N dose in two equal splits at Zadoks 14 and Zadoks 29 (main shoot and 9 more tillers) growth stages reduced N2O and GHG emissions, respectively, by 32.4% and 30.6%. Sustained N supply till grain filling produced an average of 5.1% to 10.5% higher grain yield and 2.1% to 10.5% higher grain protein content. The spectral properties recorded with PAU-LCC and SPAD meter at Zadoks 29 growth stage governed the grain yield response to fertilizer N application and can be used to fine-tune fertilizer N topdressing decisions over a wide range of varieties, locations, sowing timings and environments. [ABSTRACT FROM AUTHOR]

Summary: Predicting in-season crop yield is a unique tool for drawing important crop management decisions for precision farming. Field experiments were conducted at two locations in northwestern India under different agro-climatic zones to predict and validate spring maize yield using various in-season spectral indices. The spectral properties measured with leaf color chart (LCC), chlorophyll meter (SPAD meter), and GreenSeeker optical sensor were used to predict grain yield. A power function based on the Normalized Difference Vegetative Index (NDVI) measured with GreenSeeker optical sensor at V9 growth stage (9th leaf with fully exposed collar) presented higher values of coefficient of determination and explained 61% of the variability in spring maize grain yield, whereas NDVI measured at early and late growth stages were not reliable for the purpose. The spectral properties recorded with the SPAD meter and LCC rendered better grain yield estimates at VT growth stage (tasseling) and were respectively able to explain 75 and 76% variability in grain yield. The developed models were validated on an independent data set from another field experiment on spring maize. The normalized root mean square error (NRMSE) was <10% for LCC and SPAD at all the growth stages and at V9 growth stage for NDVI. The LCC, SPAD, and NDVI values adjusted with cumulative growing degree day were not helpful to improve NRMSE. [ABSTRACT FROM AUTHOR]

A 5-year field study was conducted to improve nitrogen (N) and phosphorus (P) use efficiencies in wheat with the synergistic use of plant growth-promoting rhizobacteria (PGPR), arbuscular mycorrhizal fungi (AMF), and spectral properties for deriving need-based fertilizer N management decisions. Bio-fertilizer consortium inoculation on wheat seed improved rhizosphere mycorrhization, albeit native mycorrhiza also produced mycorrhiza colonization. Lower mycorrhiza colonization was observed in no-P and high P treatments at 30 and 60 days after sowing (DAS) when wheat seeds were not inoculated with bio-fertilizer. However, the mycorrhiza colonization was independent of the fertilizer P level at 60 DAS in the inoculated treatments. The integrated nutrient management with bio-fertilizer and need-based N use sustained highest grain yield with 16.7% and 25% less use of fertilizer N and P, respectively. The agronomic (AE) and recovery efficiencies (RE) of applied N and P were increased by 23.0% (AEN), 21.3% (REN), 40.2% (AEP) and 49.8% (REP), respectively. On-farm validation studies exhibited improvement in partial factor productivity of fertilizer P (PFPP) by 35.8% and fertilizer N (PFPN) by 22.5% in comparison with the soil test-based recommendation. The synergistic use of bio-fertilizer and need-based N management improved the PGPR population, dehydrogenase and alkaline phosphatase activities in soil. The improved soil microbiological properties attributed to better mycorrhization and microflora propagation in soil-facilitated nutrient assimilation and thus higher N and P use efficiencies in wheat. [ABSTRACT FROM AUTHOR]

Tobacco farming is an important economic income in Brazil, although it has been challenged as regard the occupational exposure to both pesticides and nicotine endured by farmers. Chronic occupational exposure to complex mixtures can lead to health hazardous. We examined genomic instability and epigenetic changes in tobacco farmers occupationally exposed to pesticide mixtures and nicotine at tobacco fields. DNA damage was assessed by alkaline comet assay in blood cells. Genomic DNA was isolated, and telomere length was measured using quantitative polymerase chain reaction assay. We measured 5-methyl-2'-deoxycytidine, a marker of global DNA methylation, and p16 promoter methylation. The oxidative profile was evaluated by trolox equivalent antioxidant capacity and lipid peroxidation (thiobarbituric acid reactive substances) in serum. Exposure parameters, plasma cotinine and inorganic element levels, were also measured. DNA damage was significantly elevated for farmers in relation to unexposed group (P < 0.001; Mann-Whitney test) and positively associated with years of exposure. Inverse relationship between DNA damage and total equivalent antioxidant activity was demonstrated for exposed and unexposed groups. Exposed group showed significantly shorter telomeres (P < 0.001; unpaired t-test) and DNA hypomethylation (P < 0.001; unpaired t-test), as well as p16 hypermethylation (P = 0.003; Mann-Whitney test). Lipid peroxidation was increased for exposed group in relation to unexposed one (P = 0.02; Mann-Whitney test) and presented a positive correlation with global DNA methylation (P = 0.0264). Farmers have increased plasma cotinine levels (P < 0.001) and inorganic elements (phosphorus, sulphur and chlorine) in relation to unexposed group. Elevated oxidative stress levels due to chronic occupational pesticide mixtures and nicotine exposure in tobacco farmers were associated with higher DNA damage, shorter telomeres and altered DNA methylation. Telomere-accelerated attrition due to exposure may be potential intermediate step before a disease state. [ABSTRACT FROM AUTHOR]

Site-specific fertilizer nitrogen management (SSNM) could be the best management option to avoid excessive and untimely nitrogen (N) applications in wheat. Field experiments were conducted in soils of varying inherent fertility in diverse agro-climatic zones to provide SSNM strategy for wide range of wheat genotypes. The intensity of leaf colour greenness of the first fully exposed top leaf was measured using leaf colour chart (LCC) and chlorophyll meter (SPAD) at different growth stages. The spectral properties of leaves at different growth stages differed among the different wheat genotypes except at Feekes 6 stage, thus the leaf greenness measured only at this stage can be used to make SSNM decisions. After applying 25 kg N ha at planting and 45 kg N ha at Feekes 2 stage, the leaf greenness of the first fully exposed top leaf measured with LCC at Feekes 6 stage was used to decide the amount of site-specific fertilizer N to be applied as topdressing. The LCC guided fertilizer N dose sustained grain yield to the level as obtained with soil test based N applications with the less use of 20-50 kg N ha. The practice of applying additional N or just increasing number of split doses in soils with low Walkley-Black organic carbon content may not improve grain yield unless plants really need it. The SSNM strategy improved agronomic efficiency of applied fertilizer N in different wheat genotypes grown under diverse range of agro-climatic conditions and in soils with variable indigenous N supply. [ABSTRACT FROM AUTHOR]

Bagasse and rice husk are two important agro-industrial by-products that are used as fuel in the sugar and rice mill industries, thus producing large quantities of bagasse ash (BA; 0·05 of bagasse) and rice husk ash (0·20 of rice husk) as waste material. Applying BA and rice husk ash (RHA) to agricultural land improves yield, nutrient uptake and chemical fertility of soil, particularly with special reference to available phosphorus (P) and potassium (K). The present field experiment was conducted for 3 years to evaluate the P fertilizer value of these agro-industrial waste materials in a wheat–rice system (WRS). The experiment was laid out in a split-plot design with RHA and BA applied at 10 t/ha and including a no-amendment control as the main plot treatments and three levels of fertilizer P (0, 13 and 26 kg P/ha; designated P0, P13 and P26, respectively) as sub-plot treatments to wheat in WRS. Application of fertilizer P increased the wheat grain yield up to P26 in the un-amended control treatment. However, a significant response of wheat to fertilizer P was also observed up to P13 in the presence of BA and RHA, thereby saving 50% of fertilizer P. Both RHA and BA increased wheat productivity by 12 and 16%, respectively, over the un-amended control. The subsequent rice crop also produced 14% higher paddy yield when the two ashes were applied along with P13 to the previous wheat crop. The increases in grain yield were accompanied by significant increases in the uptake of P and K, and P content (Olsen P) in the soil. The application of recommended P (P26) in un-amended plots resulted in a negative P balance of 9·3 kg P/ha/year. On the other hand, the application of BA alone and RHA along with P13 resulted in neutral/slightly positive P balance. A strong linear relationship (R2 = 0·98) was observed between P balance and Olsen-P build up in the soil. It may be concluded that application of BA and RHA has the potential to increase system productivity and reduce the cost of inputs in terms of reduced application of fertilizer P to wheat and rice. [ABSTRACT FROM PUBLISHER]

Blanket fertilizer nitrogen (N) recommendations for large irrigated transplanted rice tracts lead to low N use-efficiency (NUE) due to field-to-field variability in soil N supply and seasonal variability in yield. To achieve high NUE, a fertilizer N management strategy based on visible and near-infrared spectral response from plant canopies using a GreenSeeker™ optical sensor was evaluated. Seven field experiments were conducted during 2005-2007 at two locations in the Indo-Gangetic plains of South Asia to define relationships between in-season sensor measurements at panicle initiation (PI) stage and up to 2 weeks later, and yield of rice. During 2006-2010, seven field experiments were conducted to assess the sensor-based N management strategy and to work out the prescriptive N management to be followed prior to applying sensor-guided fertilizer dose. During 2010 and 2011, the sensor- based N management strategy was evaluated versus farmers' fertilizer practice at 19 on-farm locations. Relationships with R values 0.51 (n = 131), 0.45 (n = 74) and 0.49 (n = 131), respectively, were observed between in-season sensor-based estimates of yield at 42 (PI stage), 49 and 56 days after transplanting of rice and actual grain yield of rice. Applications of 30 kg N ha at transplanting and 45 kg N ha at active tillering stage were found to be the appropriate prescriptive strategy before applying the GreenSeeker-guided dose at PI stage. Sensor-guided N management resulted in similar grain yields as the blanket rate farmer practice, but with reduced N rates, i.e. greater recovery efficiency (by 5.5-21.7 %) and agronomic efficiency [by 4.7-11.7 kg grain (kg N applied)]. This study revealed that high yields coupled with high NUE in transplanted rice can be achieved by replacing blanket fertilizer recommendation by an optical sensor-based N management strategy consisting of applying a moderate amount of fertilizer N at transplanting and enough fertilizer N to meet the high N demand during the period between active tillering and PI before applying a sensor-guided fertilizer N dose at PI stage of rice. [ABSTRACT FROM AUTHOR]

Blanket fertilizer nitrogen (N) recommendations for large irrigated wheat tracts lead to low N-use efficiency due to field-to-field variability in soil N supply and seasonal variability in yield. To achieve high N use efficiency, a site-specific N management strategy using GreenSeeker™ optical sensor was evaluated. We conducted seven field experiments during 2004-2006 at three locations to define relationships between in-season sensor measurements and yield of wheat and to know whether response of wheat to fertilizer N can be estimated by sensor measurements. During 2005-2007, four field experiments were conducted to assess the sensor-based N management strategy and to work out prescriptive N management to be followed prior to applying sensor-guided fertilizer dose. We observed robust relationships between in-season sensor-based estimates of yield at Feekes 5-6 and 7-8 stages and actual wheat yields. Response of wheat to fertilizer N defined by the sensor was highly correlated with harvest response index. Sensor-guided fertilizer N applications resulted in high yield levels and high N-use efficiency. Application of 90 kg N ha at planting or in two equal doses at planting and crown root initiation stage was the appropriate prescriptive fertilizer N management. This study reveals that high N-use efficiency in irrigated wheat can be achieved by replacing blanket fertilizer recommendation by an optical sensor-based N management strategy consisting of applying moderate amount of fertilizer N at planting and crown root initiation stages and sensor-guided fertilizer N dose at Feekes 5-6 or 7-8 stages of wheat. [ABSTRACT FROM AUTHOR]

Fertilizer nitrogen (N) is one of the major inputs in rice-wheat production systems in South Asia. As fertilizer N has generally been managed following blanket recommendations consisting of two or three split applications of preset rates of the total amount of N, improvement in N use efficiency could not be achieved beyond a limit. Feeding crop N needs is the most appropriate fertilizer N management strategy to further improve N use efficiency. Since plant growth reflects the total N supply from all sources, plant N status at any given time should be a better indicator of the N availability. The chlorophyll meter and leaf colour chart have emerged as diagnostic tools which can indirectly estimate crop N status of the growing crops and help define time and quantity of in-season fertilizer N top dressings in rice and wheat. Supplemental fertilizer N applications are thus synchronized with the N needs of crop. The chlorophyll meter may not be owned by South Asian farmers individually, but it can be made available to farmers through village cooperatives, extension specialists, and crop consultants. Leaf colour chart, a simple and cost-effective device has already penetrated into South Asian farming and increasing numbers of farmers are finding it helpful in efficiently managing N fertilizers. This paper reviews the results of investigations carried out using these diagnostic tools in managing need based N applications in rice and wheat in South Asia. [ABSTRACT FROM AUTHOR]

Neem coated urea (NCU) applied to rice can result in high N use efficiency as it contains nitrification inhibition properties. Field experiments were conducted for three years (2005–2007) at Ludhiana (sandy loam soil) and Gurdaspur (clay loam soil) for evaluating the relative performance of NCU vis-à-vis ordinary urea as a source of N for transplanted wetland rice. Along with a no-N control, the two N sources were tried at three N levels––40, 80 and 100% of the recommended level of 120 kg N ha−1. Different doses of N were applied in three equal split doses at transplanting, 21 and 42 days after transplanting (DAT). For need based site specific N management for improved N use efficiency, the two sources of N were applied using leaf colour chart (LCC). In this treatment a basal dose of N at the rate of 20 kg N ha−1 was applied after 7 DAT and LCC readings were recorded at weekly intervals starting 14 DAT. Whenever the intensity of green colour of the first fully opened leaf from the top was less than shade 4 of the LCC, N was applied at the rate of 30 kg N ha−1. The application of N through NCU and ordinary urea increased the rice grain yield significantly with increasing levels of N at both the locations. The application of NCU at recommended rate (120 kg N ha−1) produced significantly higher rice grain yield than the yield obtained with ordinary urea at Ludhiana. The differences were not significant at Gurdaspur. Need based N management using LCC revealed that rice required only 110 kg N ha−1 at Ludhiana and 80 kg N ha−1 at Gurdaspur, irrespective of the N sources. The application of NCU using LCC produced significantly higher (8.6%) rice grain yield than ordinary urea at Ludhiana but increase was not significant at Gurdaspur. The superiority of NCU over ordinary urea at Ludhiana was accompanied by spectacular increase in N uptake and nitrogen use efficiencies when applied on soil test basis or using of LCC. [ABSTRACT FROM AUTHOR]

Abstract  Poultry litter (PL) is an important nutrient source; however, no information is available regarding its value in supplying N and P in rice–wheat (RW) production. A three-year field study was conducted at Ludhiana, Punjab, India on a loamy sand soil to identify optimum combination of PL and N and P fertilizers for a sustainable RW production. The litter was applied to rice at 5 Mg ha−1 as a single application and supplemented with different rates of N. The residual effect of PL and the direct effects of the different combinations of N and P were studied in the following wheat. Nitrogen and P mineralization from PL was studied under controlled conditions in the laboratory, and macronutrient input–output balances were estimated from field results. About 46% of the N from PL was released after 60 days of incubation. The release of P from the PL occurred mainly during the initial 20 days after incubation, accounting for 15–17% of the total P. Combining PL with fertilizer N (40 kg ha−1) increased rice yield and nutrient uptake similar to what was obtained with the application of recommended fertilizer N (120 kg ha−1). In the following wheat, the residual effect of PL was equal to 30 kg N ha−1 and 13 kg P ha−1. After three annual cropping cycles and PL application, mean soil organic C increased by 17%, Olsen-P by 73%, and NH4OAc-extractable-K by 24%. Most treatments had positive P but negative K balances. About 11% of the net P balance was recovered from the soil as Olsen-P. The study showed that optimum N and P fertilizer doses for an RW system receiving 5 Mg ha−1 of PL are 40 kg N ha−1 for rice and 90 kg N + 13 kg P ha−1 for the following wheat. Safe and effective management of PL should be based on P balance, particularly when regular applications of PL are to be made in the RW system. [ABSTRACT FROM AUTHOR]

Abstract  The contribution of different sized soil separates to various inorganic P fractions was investigated after 32 years of long-term fertilization under maize-wheat-cowpea fodder crop rotation. Phosphorus was applied as single super phosphate. A major portion (71.5%) of Olsen-P was extracted from sand size particles, and only 11.4% and 17.1% was present in silt and clay size separates of the surface soil layer, respectively. Unlike Olsen-P, Al-P and Fe-P in soil were mainly present in the clay fraction of the soil. Percent contribution of clay, sand and silt particles in the surface layer was 61.5, 27.4 and 11.1 to Al-P, and 66.4, 21.6 and 12.0 to Fe-P, respectively. However, Ca-P in surface soil layer was mainly (68%) present in sand size soil separates followed by silt (28.5%) and clay (3.5%) size soil separates. Percent distribution of P forms in different sized soil separates of the subsurface layer also followed the same pattern, but there was little decrease in the contribution of sand with a corresponding increase in the contribution of silt and clay size soil separates. X-ray diffractograms specified the precipitation of residual fertilizer P as octa-calcium phosphate, hydroxy apatite and variscite, after reacting with calcium and aluminum in the soil. The peaks recognizing the presence of these reaction products were observed only in sand and silt size soil separates. However, no peak was found in clay sized soil separates. [ABSTRACT FROM AUTHOR]

Abstract  Transformations of applied phosphorus (P) to unavailable residual soil P is the major cause of limited P supply in most of the P-deficient soils. The effect of the incorporation of crop residues (rice straw [RS] and wheat straw [WS]) and organic manures (farmyard manure [FYM] and green manure [GM]) on P release in soil and its bio-availability to various summer and winter crops was investigated in laboratory and screen house experiments. Surface (0–0.15 m) soil samples collected after 32 years of differential fertilization to maize–wheat–cowpea fodder crop rotation, were examined for adsorption/desorption behavior of P, after incubating with organics of varying C:P ratios. Incorporation of crop residues increased P adsorption maxima as well as resistance to P release in soils. Increased buffering capacities in crop residue-incorporated treatments decreased P desorption in soil, whereas the incorporation of organic manures decreased P sorption, maximum buffering capacity (MBC), bonding energy, and increased P concentration in soil solution. Although the incorporation of crop residues decreased P release in soil its bio-availability in the soil–plant system was crop-specific and varied with the time of incorporation of organics. Raya showed increased P uptake with incorporation of both RS and WS, whereas in the case of berseem increased P uptake occurred only with wheat straw. Phosphorus uptake in rice, maize, and soybean decreased with the incorporation of both RS and WS. Incorporation of crop residues 1 day before the sowing of summer crops decreased P uptake, whereas incorporation 3 weeks prior to the sowing of winter crops improved P bio-availability. Incorporation of organic manures with a narrow C:P ratio, however, improved P uptake in all the crops under investigation, in both the seasons. The results thus emphasized that adsorption parameters calculated from the examination of soil samples should not be used independently for making fertilizer P recommendations. Crop effects (root exudates) and their interaction with P reaction products in soil and synchronization in P release from organics and crop uptake need to be considered to understand the virtual behavior of P bio-availability in the soil–plant system. [ABSTRACT FROM AUTHOR]

Abstract  Phosphorus availability from residual P sources in soil is virtually the chemistry of metastable P compounds, i.e., their solubility and interaction with other soil and plant components. Identification of these compounds in soils under long-term application of fertilizers and farmyard manure is unstated and is prerequisite to comprehend the processes of P transformations and cycling in soil-plant system. X-ray diffraction analysis of surface and subsurface soils fertilized for 32 years under a maize–wheat–cowpea (fodder) cropping sequence revealed that P reaction products in soil depends upon the kind of fertilizer added to the soil as well as on management practices. Precipitation of applied P occurred mainly as octa-calcium phosphate, hydroxy apatite and variscite. In addition to these compounds, precipitation as $$\hbox{CaNH}_{4}\hbox{PO}_{4}\cdot\hbox{H}_{2}\hbox{O}$$ was also observed in soil receiving diammonium phosphate rather than super phosphate as a fertilizer P source. Continuous application of farmyard manure (FYM) for three decades inhibited the conversion of applied P to more stable forms such as variscite and hydroxy apatite. The different P reaction products govern the availability of residual soil-P to growing plants. The reaction products formed were associated only with the sand and silt fraction of soil. Phosphorus in the clay fraction is mainly P adsorbed on exchange complexes or entrapped in lattice of silicate minerals. [ABSTRACT FROM AUTHOR]

Abstract  An understanding of the adsorption–desorption behaviour of phosphate (P) in soils after three decades of long-term fertilization would be an invaluable supplement to our knowledge of the chemistry of P in soils and would assist in developing P application strategies for successive crops. With this objective and within the framework of a long-term experiment, we collected surface soil samples (0–0.15 m) from agricultural crop land on which a rotation of maize-wheat-cowpea (fodder) crops had been grown for 32 years. The soil samples were investigated for adsorption and desorption behaviour of P, and the buffering capacities of soil samples were computed from the adsorption data. Soils differed widely in their P supply characteristics. Phosphate adsorption increased while percentage P adsorbed decreased gradually with increasing levels of added P. Adsorption maxima and the extent of P adsorption was at its maximum in unfertilized soil, and P adsorption decreased with increased P applications. The incorporation of farmyard manure with optimal P levels decreased P adsorption even more than a super-optimal application of P fertilizers. Bonding energy and Freundlich constant ȁ8nȁ9 also decreased with increased P application and with the incorporation of farmyard manure. The adsorption and desorption of applied P were inversely related, and the soils that adsorbed P the most readily released it the least into the soil solution, and vice-versa. Computation of maximum buffering capacities (MBC) indicated that increased levels of P application decreased MBC and increased P supply in soil. The beneficial effects of an annual incorporation of farmyard manure with optimal P levels were clearly pronounced, and P availability in these soils was found to be even higher than the soil receiving the super-optimal application of P fertilizers. Various adsorption–desorption parameters were significantly related with the P uptake of different summer (rice, maize, soybean) and winter (wheat, berseem and raya) crops. Adsorption maxima, desorption maxima and maximum buffering capacity are the major parameters governing P availability in soils. [ABSTRACT FROM AUTHOR]