Mineralization of Nitrogen from Nitrogen-15 Labeled Crop Residues and Utilization by Rice
- R. J. Norman ,
- J. T. Gilmour and
- B. R. Wells
The availability of N from the residues of the previous crop to the subsequent rice (Oryza sativa L.) crop is largely unknown. The objectives of this study were to (i) measure the mineralization of N from 15N-labeled rice, soybean (Glycine max L.), and wheat (Triticum aestivum L.) residues and the uptake by a subsequent rice crop; and (ii) compare the 15N tracer method with the standard fertilizer-N response method used in field studies to quantify the N contribution from the crop residue to the next crop. Nitrogen mineralization from decomposing crop residues was measured by soil sampling prior to seeding the rice crop and after seeding by plant sampling the rice at maturity. 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. The 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.
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