The Release of Nitrogen from Sulfur‐coated Urea as Affected by Soil Moisture, Coating Weight, and Method of Placement

Abstract

Abstract Information on the release of N from sulfur‐coated urea (SCU) as affected by soil moisture in the aerated range is lacking. Laboratory incubation experiments were therefore conducted on two soils to study the release of N from SCU as affected by soil moisture in the aerated range, coating weight (SCU‐28 and SCU‐9), and method of placement (on one soil only). In the calcareous Princes Town soil the release of N from SCU increased with increasing moisture throughout the 9 weeks of study. In acid Talparo soil similar trends were present up to 3 weeks, but at 6 and 9 weeks maximum release of N occurred at medium moisture (soil moisture at pF 2.4) and minimum release at low moisture (soil moisture at pF 3.5). In Princes Town soil the difference in release of N from SCU‐28 and SCU‐9 remained throughout the 9 weeks. By 9 weeks SCU‐9 (heavy coat) released more N at high moisture level (soil moisture at pF 1.0) than SCU‐28 (light coat) at low moisture. In Talparo soil the effect of coating weight on the release of N at three moisture levels was considerably reduced from 6 weeks onwards. Ammonia volatilization losses were recorded only with Princes Town soil but they never exceeded 2.5% of the total N applied. The release of N from SCU was faster when the granules were mixed with the soil rather than surface applied. This difference between surface and mixed application was greater at high soil moisture levels.