Nitrogen mineralization, microbial biomass and crop yield as affected by wheat residue placement and fertilizer in a semi-arid tropical soil with minimum tillage.
The effects of wheat residue placement and chemical fertilizer on microbial biomass, N-mineralization and crop yield were examined in a fallow-rice cv. Akashi-lentils cv. Pant 209 crop rotation at the Banaras Hindu University, Uttar Pradesh, India. Available N ranges were 7.1-10.4µg g-1 in control plots, 11.6-17.3 µg g-1 in plots given NPK fertilizer, 8.5-13.3 µg g-1 in plots treated with 2 kg m-2 wheat residue, and 9.6-13.7 µg g-1 in those treated with wheat residue plus fertilizer. NaHCO3-Pi ranges in the soil were 9.0-12.0 µg g-1 in control plots, 11.2-16.0 µg g-1 in fertilized plots, 10.2-14.2 µg g-1 in wheat residue plots and 12.2-16.7 µg g-1 in plots amended with wheat residue plus fertilizer. Treatment with wheat residue plus fertilizer resulted in the maximum rate of N-mineralization, followed by the fertilizer and then by the wheat residue treatment. The mineralization rate ranges were 3.4-9.8, 4.2-14.3, 4.0-11.2 and 4.6-16.6 µg g-1 N month-1 for control, fertilizer, wheat residue and wheat residue plus fertilizer-treated plots, respectively. The maximum effect of inputs on microbial biomass was realized under the wheat residue plus fertilizer treatment, followed by wheat residue, and was least in fertilizer plots. Both crop biomass and grain yield showed a maximum response to the wheat residue plus fertilizer application. Aboveground crop biomass ranges were 679-991 g m-2 for the rice crop and 390-675 g m-2 for the lentil crop. Grain/seed yields were 108-146 g m-2 and 102-174 g m-2 for the rice and lentil crops. It is concluded that wheat residue applied in combination with fertilizer to a rice-lentil rotation under rainfed, reduced tillage cultivation increased the activity of soil OM, thereby enhancing the nutrient supply rate, which in turn resulted in better crop growth and grain yield.