Fate of Fertilizer Nitrogen in a Flooded Rice Soil

Abstract

AbstractIn order to improve the efficiency of fertilizer N utilization by rice (Oryza sativa L.), it is important to know what happens to N applied to the soil. Field experiments utilizing 15N‐enriched ammonium sulfate were carried out to determine the fate of fertilizer N (100 kg N/ha) applied to Crowley silt loam soil. The distribution of fertilizer N in the plant‐soil system at harvest time was determined using 2.32 m2 plots. The distribution of fertilizer N in the plant‐soil‐floodwater system at six times during the growing season was measured in smaller plots (0.28 m2).The results from the larger plots showed that fertilizer N recovered in the grain ranged from 30.9 to 37.3 kg N/ha depending on the method of application. Recovery of fertilizer N in the straw ranged from 18.2 to 24.2 kg N/ha. A considerable portion of fertilizer N (24.2 to 27.1 kg N/ha) remained in the soil (including roots) after cropping. Total recovery of the 100 kg/ha addition of labelled fertilizer N in the soil‐plant system was 75.0 to 85.6 kg N/ha for the different methods of N application examined. Experiments using the smaller 0.28 m2 plots showed rapid uptake of fertilizer N immediately after application, with no apparent further uptake after about 3 weeks. Soil N was the major and perhaps sole source of N for the plant during the last part of the growing season.