| Abstract: | Abstract A laboratory study was used to simulate the pattern of diffusion of ammonium and nitrate ions in flooded soil. Ammonium, deep incorporated in a submerged irrigation system, diffused upward from the anaerobic to the aerobic layer where biochemical oxidation nitrified it to NO2 and NO3. These oxidized N species diffused downward from the aerobic layer to the anaerobic layer where most or at least partly, was lost as gaseous end products. Three crops of rice were grown in a glasshouse experiment to estimate N use efficiency under various combinations of irrigation and N management practices. Overall N use efficiency averaged 45%. Under continuous flooding, almost two thirds of the applied fertilizer N (647% use efficiency) was recovered by the rice crop. Under alternate flooding and drying, the response was very poor, with only about one fourth (26% use efficiency) of the applied fertilizer N being recovered by the crop. This demonstrated importance of the proper combination of irrigation and fertilizer management in paddy soils to maximize N utilization. |
