Losses of Nitrogen from Some Flooded Soils in Tracer Experiments

Nitrogen losses were measured in laboratory and greenhouse experiments in four flooded soils after addition of 15 N‐tagged (NH 4 ) 2 SO 4 or rice straw after various incubation periods. Substantial losses occurred in all cases except where NH 4 + ‐N was rapidly immobilized and/or fixed by clay minerals. The necessity for nitrification as a prelude to N loss was demonstrated by showing that no loss occurred when oxygen was excluded and that where no nitrate was produced, no N 2 was evolved. Growing rice plants ( Oryza sativa ) effectively reduced the magnitude of the nitrogen loss.