Carbon and nitrogen fractions in soil during maize growth under long-term fertilizer management practices to maize-wheat cropping

A field experiment was conducted to study the effect of long-term fertilizer management (viz. control, 100% N, 100% NP, 100% NPK and 100% NPK+FYM) on the carbon (C) and nitrogen (N) fractions in soils under maize-wheat cropping. Soil samples were collected from on-going experiment (started in 1971) during maize growing season in kharif 2011 to discern long-term effect of field treatments on changes in different pools of C and N viz. soil organic C (SOC), water soluble C (WSC) and KMnO₄ oxidizable C (KMnO₄-C) and ammonical-N (NH₄⁺-N) and nitrate-N (NO₃⁻-N) content. Soil samples were analyzed after 1, 3, 5, 7 and 9 weeks interval during maize growth period. The SOC, NO₃⁻-N and NH₄⁺-N concentration increased significantly with combined application of NPK+FYM as compared to the control. The concentration of SOC increased after 3 weeks, and was reached the highest at harvesting. However, the WSC and KMnO₄-C concentration increased up to 5^th week after sowing and it decreased afterwards. The NO₃⁻-N and NH₄⁺-N concentration decreased with increased maize growth stage, and decreased to the lowest value at harvesting. The dry matter yield of maize at maturity correlated well with SOC, WSC, KMnO₄-C, NH₄⁺-N and NO₃⁻-N concentration. Crop yield of maize and N uptake increased with NPK+FYM application at all growth stages.