Search

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]

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]

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]