Effect of Addition of New Crop Residues on Recovery of 15n Previously Added Residues by Maize

A research was conducted to evaluate the effect of addition of new crop residues on recovery N at two crop cycle by maize. Two crops residue (rice straw=RS and soybean=SY) were grown in a glass-house under four 15N concentration, i.e, 0 mM (N0), 0.625 0 mM (N1), 2.5 0 mM (N2), and 10 mM (N3) supplied as CO(15NH2)2, in plastic pots containing 5 kg of quartz sand. The maize as plant pots containing 10 kg of soil and placed in the glasshouse, it was conducted to evaluate the microbial biomass N and recovery N by maize and to find of stimulation and retardation on mineralized nitrogen. 15N-labelled crop residues added at the first crop cycle and unlabelled crop residues of the same species added at the second cycle. The result showed that the recovey of 15N from crop residues during the first planting ranged from 71.36% (RSN1) to 80.64% (RSN3). During the second planting with no addition of new crop residues ranged from 4.54% (SYN3) to 28.29% (RSN3), while that with addition of new crop residues ranged from 8.12% (SYN3) to 18.55% (RSN3). Repeated addition of unlabelled SY and RS residues showed stimulation of N mineralization (2.50% to 3.63 in SY) but RS residues showed retardation of N mineralization (1.88% to 9.74%).