Microbial degradation of 15n-labeled rice residues in soil during two years' incubation under flooded and upland conditions:I. decay of residue and soil microfiora

Abstract

The decay oC rice residue was investigated after incubation periods oC Crom 1 to 24 months at 30°C under both flooded and upland soil conditions. Tops and roots oC rice plants were cut into about 10-mm length, and separately incorporated in soil which had been passed through a 0.5-mrn sieve. Plant debris were Cractionated physically according to their sizes and divided into five groups (>4 mrn, 4-2 mm, 2-1 mm, 1-0.5 mrn, and 0.5-0.25 mrn). Carbon Joss Crom the soils amended with rice residues and decrease in the weight oC total plant debris proceeded at a rapid speed in the early periods (around 4 months) and then at a slow speed in the subsequent periods under both flooded and uplana soil conditions. The distribution oC the plant debris in the decomposition processes differed under flooded and upland conditions. Under flooded conditions, 2-4 mrn-sized plant debris were retained for a long period with slow transCormation into the smaller Cractions. In contrast, under upland conditions, change oC plant debris Crom large to small size Cractions proceeded gradually. This continuous change could be attributed to the high decomposing activities oC Cungi under upland conditions. © 1980 Taylor & Francis Group, LLC.