MINERALIZATION OF NITROGEN FROM N-15 LABELED CROP RESIDUES AND UTILIZATION BY RICE

Measured the mineralization of N from 15N-labeled rice, soybean Glycine max, and wheat Triticum aestivum residues and the uptake of a subsequent rice Oryza sativa crop. The minimum estimate of the amount of residue N mineralized from the time of residue incorporation until rice harvest was 9, 52, and 38% of the rice, soybean and wheat residue N, respectively. Amount of residue N recovered in the rice crop was 3, 11, and 37% of the rice, soybean, and wheat residue N, respectively. The lower the C/N ratio and the higher the amount of N in the residue, the lower was the amount of residue N recovered in the soil organic fraction at harvest and the higher was the amount of residue N mineralized. The 15N tracer method compared favorably with the fertilizer N response method when the uptake efficiency of the fertilizer N was taken into account. -from Authors