Estimation of nitrogen fixation in nutrient management options under soybean-wheat cropping sequence in an ustochrepts soil

Abstract

Soybean- wheat is the dominant cropping system grown on Madhya Pradesh due to congenial climate, development of agro industries and export opportunities. Both are high value crops and raising them using organics may further improve product quality and help in sustaining system productivity on long term basis. A study on impact assessment of nutrient management options and estimation of nitrogen fixation by soybean under different nutrient management options was studied on soybean wheat system. For estimation of nitrogen fixation annual input output N balance technique was used. The experiment was initiated in Kharif 2015 comprising the nine treatments, viz control (no fertilizer and no manure), 100% RDF, 50% RDF + 50% FYM, 50% RDF + 50% VC, 100% FYM, 100% VC, 100% RDF + 25 kg ZnSO4 (First year), 100% RDF (DAP as a source of P) and 100% RDF + 0.5 kg Ammonium molybdate in both the crops with three replication arranged in a randomized block design. The estimated amount of nitrogen fixed by soybean annually varied from 54.91 to 67.46 kg/ha, however net gain of nitrogen in soil after offsetting the nitrogen derived by soybean ranged from 26.11 kg ha-1 in control to 9.47 kg ha-1 in 100% RDF + Zn, 8.99 kg ha-1 in 100% RDF + 0.5 kg AM, 4.94 kg ha-1 in 100% RDF, 4.52 kg ha-1 in 50% RDF + 50% Vermi-compost annually depending upon the mode of nutrient supply kg/ha, annually. Maximum nitrogen gain was recorded 67.46 kg ha-1 on 100% RDF + Zn nutrient option. There was a linear relationship between the amount of harvestable biomass nitrogen and residual biomass nitrogen. The highest percentage of nitrogen derived from atmosphere(%Ndfa) was recorded in the control treatment, but the highest amount of nitrogen (104.8 kg ha-1) fixed was found in the 50% RDF+50% Vermi Compost nutrient option. Conjunctive use of organic and inorganic source of nutrient is the best option to harness the nitrogen fixation potential of soybean.