Nitrogen cycling in a 15N-fertilized bean (Phaseolus vulgaris L.) crop

To increase our understanding of the fate of applied nitrogen in Phaseolus vulgaris crops grown under tropical conditions, 15N-labelled urea was applied to bean crops and followed for three consecutive cropping periods. Each crop received 100 kg urea-N ha-1 and 41 kg KCl-K ha-1. At the end of each period we estimated each crop's recovery of the added nitrogen, the residual effects of nitrogen from the previous cropping period, the distribution of nitrogen in the soil profile, and leaching losses of nitrogen. In addition, to evaluate potential effects of added phosphorus on nitrogen cycling in this crop, beans were treated at planting with either 35 kg rock-phosphate-P, 35 kg superphosphate-P, or 0 kg P ha-1. Results showed that 31.2% of the nitrogen in the first crop was derived from the applied urea, which represents a nitrogen utilization efficiency of 38.5%, 6.2% of the nitrogen in the second crop was derived from fertilizer applied to the first crop, and 1.4% of the nitrogen in the third crop. (orig./AJ)