A summary of placement and fall versus spring application of nitrogen fertilizers

Non-Peer ReviewedIn 52 field experiments since 1973-74, the yield of barley grain without N averaged 1570 kg/ha, but the yield was increased by fall and spring application of incorporated urea (56 kg N/ha) to 2540 and 3470 kg/ha, respectively. Early fall application was only half as efficient as late fall application. In five field experiments with 15N, the recovery in the spring of fall applied nitrate was low (13 to 60 %) while recovery of late fall banded ammonium was much higher (82 to 99 %). These losses came about through denitrification and not by leaching. Variable amounts of applied nitrate and ammonium were immobilized in the soil. Fall banding (45 cm spacing) and fall nesting (45 × 45 cm spacing) of urea (or aqua ammonia) gave larger yield increases than fall incorporation. In five experiments before 1978-79, yield increases of barley grain from fall application of urea by incorporation, banding and nesting were 960, 1240, and 1560 kg/ha, respectively. In the same order, yield increases were 740, 1100, and 1510 kg/ha in ten more recent experiments. However, the size of yield increases from fall banding were variable from experiment to experiment, ranging from being similar to fall incorporation to being similar to the high-yielding fall nests. With spring application of urea, banding produced slightly higher yields than incorporation, while nesting tended to produce lower yields. Retaining rather than removing the straw of the previous crop depressed the yield of barley grain by 650 kg/ha in six field experiments, and the retention of straw halved the uptake of fertilizer N by the crop. Preliminary results suggest that placement of fertilizer N in large pellets may overcome the immobilization of fertilizer N by the straw