Transformations and Movement of Urea in Soils

Abstract

Abstract Samples of several California soils were incubated in a controlled environment chamber after addition of varying amounts of urea in solution. Samples were analyzed after time intervals ranging from 1 day to 8 weeks. In short‐term experiments analyses for residual urea were performed at frequent, short intervals, and in longer‐term experiments nitrification of the hydrolysis product was followed. At 45°F., 200‐ and 400‐ppm. amounts of urea were completely hydrolyzed after 7 days, although some urea remained after 3 days. At 75°F., no urea remained after 2 days when the initial application was 400 ppm or less. At 800 ppm., considerable urea remained at 3 days but none at 14 days. Urea was rapidly nitrified in all soils at moderate levels of application but was inhibited in the poorly buffered Hanford sandy loam by the 800‐ppm. application, due to the high pH produced. Leaching experiments with soil columns showed that urea moves less rapidly than nitrate, partly because of rapidly hydrolysis to ammonia and partly because urea itself is held by weak absorption forces.