Decomposition of rice residue in tropical soils

Nitrogen uptake by rice plants from rice straw incorporated, fertilizer (ammonium sulfate), and soil was investigated using 15N as a tracer in pot experiments conducted in the greenhouse of the International Rice Research Institute in the Philippines. The nitrogen from fertilizer was rapidly absorbed in an early growth stage. The nitrogen from straw was absorbed in an early growth stage but absorption was at its peak in the middle growth stage. The nitrogen from soil was absorbed in a pattern similar to that observed in absorption from straw but absorption was at its peak in a later growth stage. The distribution pattern of mineralized nitrogen of three sources in soil was similar with the uptake pattern of nitrogen in plants. The recovery of straw nitrogen in the plants was 25 per cent after 130 days.