Fertilizer nitrogen recovery and biological nitrogen fixation in fababean?sugar beet and spring wheat?fababean cropping sequences

Abstract

The recovery of15N labelled ammonium fertilizer as well as biological N2 fixation of fababean (Vicia faba minor) was studied in two cropping sequences: fababeansugar beet and spring wheat-fababean. With fababean as the first crop, 20 kg N ha−1 labelled with 11.4%15N atom excess (a.e.) was applied. The fertilizer N recovery of the first crop of fababean was 15.8%. Whereas 82% of the N in the fababean was derived from the atmosphere through biological fixation, 16% came from soil and only 2% from fertilizer. The recovery of residual labelled fertilizer N by the subsequent sugarbeet crop was 3.9%. The total fertilizer N recovery over the two years was therefore about 20%. In the second cropping sequences, 50 kg N ha−1 labelled with 11.3%15N a.e. was applied to spring wheat. The fertilizer N recovery of spring wheat was 36.0% in this sequence. 20% of the N in the spring wheat was derived from fertilizer and the remaining 80% from soil. 1.6% of the residual labelled fertilizer was recovered by the subsequent fababean crop. The total recovery of fertilizer N in the second sequence was therefore about 38%. The recovery by the first crop almost entirely determined the total N recovery over the two years cropping sequences.