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The efficient (site-specific) management of soil nutrients is possible by understanding the spatial variability in distribution of phyto-available nutrients (here after called available nutrients) and identifying the soil management zones (MZs) of agricultural landscapes. There is need for delineating soil MZs of agricultural landscapes of the world for efficient management of soil nutrients in order to obtain sustainability in crop yield. The present study was, therefore, undertaken to understand the spatial distribution pattern of available micronutrients (zinc (Zn), boron (B), iron (Fe), manganese (Mn) and copper (Cu)), available sulphur (S), and soil properties (soil acidity (pH), electrical conductivity (EC) and organic carbon (SOC) content) in soils of intensively cultivated Indo-Gangetic Plain (IGP) of India and to delineate soil MZs for efficient management of soil nutrients. Totally, 55101 soil samples from 0-15 cm depth were obtained from 167 districts of IGP during 2014 to 2017 and were analysed for different soil parameters. Soil pH, EC and SOC content varied from 4.44 to 9.80, 0.02 to 2.13 dS m-1 and 0.10 to 1.99%, respectively. The concentration of available Zn, B, Fe, Mn, Cu and S varied from 0.01 to 3.27, 0.01 to 3.51, 0.19 to 55.7, 0.05 to 49.0, 0.01 to 5.29 and 1.01 to 108 mg kg-1 , respectively. Geostatistical analysis resulted in varied distribution pattern of studied soil parameters with moderate to strong spatial dependence. The extent (% area) of nutrient deficiencies in IGP followed the order: S > Zn > B > Mn > Cu > Fe. Principal component analysis and fuzzy c-means clustering produced six distinctly different soil MZs of IGP for implementation of zone-specific soil nutrient management strategies for attaining sustainability in crop yield. The developed MZ maps could also be utilized for prioritization and rationalization of nutrients supply in IGP of India.

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PNSS P89/2BSummary A computational exercise was undertaken to quantify the percent N derived from atmosphere %Ndfa) in soybean and consequent N benefit from biological N 2 -fixation process annually accrued to the soil by the soybean crop using average annual N-input/-output balance sheet from a 7 yr old soybean-wheat continuous rotational experiment on a Typic Haplustert. The experiment was conducted with 16 treatments comprised of combinations of four annual rates of farmyard manure (FYM @ 0, 4, 8, and 16 t ha ±1 ) and four annual rates of fertilizer N (@ 0, 72.5, 145, and 230 kg N ha ±1 ) applications. The estimated N contributed through residual biomass of soybean (RBN S ) consisting of leaf fall, root, nodules, and rhizodeposition varied in the ranges of 7.02±16.94, 11.65±28.83, 3.31± 8.91, and 11.3±23.8 kg N ha ±1 yr ±1 , respectively. A linear relationship was observed between RBN S and harvested biomass N (HBN S ) of soybean in the form of RBN S = 0.461 HBN S ± 20.67 (r = 0.989, P < 0.01), indicating that for each 100 kg N assimilated by the harvested biomass of soybean, 25.4 kg N was added to the soil through residual biomass. The Ndfa values ranged between 13% and 81% depending upon the annual rates of application of fertilizer N and FYM. As per the main effects, the %Ndfa declined from 76.4 to 26.0 with the increase in annual fertilizer-N application from 0 to 230 kg N ha ±1 , whereas %Ndfa increased from 40.8 to 65.8 with the increase in FYM rates from 0 to 16 t ha ±1 , respectively. The N benefit from biological N 2 fixation accrued to the soil through residual biomass of soybean ranged from 7.6 to 53.7 kg N ha ±1 yr ±1 . The treatments having %Ndfa values higher than 78 showed considerable annual contribution of N from N 2 fixation to the soil which were sufficient enough to offset the quantity of N removed from the soil (i.e., native soil N / FYM-N / fertilizer-N) with harvested biomass of soybean.