Recovery of wheat residue nitrogen~(15) and residual effects of N fertilisation in a wheat - wheat cropping system under mediterranean conditions

摘要

For cropping systems, quantification of the fate of fertiliser N and residual N is essential, to develop management practices that optimise N use efficiency. A field study was conducted in Saharan Morocco to assess the fate of fertiliser N in a wheat (Triticitm durum var. Kari m) - wheat cropping sequence. Therefore 85 kg ha~(-1) N as labelled ammonium sulfate (9.764 percent atomic excess) was applied in a three-split application. Fertiliser N recovery by wheat in the first year was 33.1 percent. At harvest, 64.8 percent of fertiliser N was found in the 0 - 80 cm profile as residual fertiliser-derived N; 2.1 percent of the applied N could not be accounted for year 1996/1997. The N unaccounted for was mainly ascribed to denitrification. The recovery of the residual labelled fertiliser N by the subsequent wheat crop was 6.4 percent for the treatment without residue incorporation, and 7.4 percent in the case of residue incorporation. The un recovered N after the second cropping season was 15.6 and 11.8 percent without and with residue incorporation, respectively. Loss of labelled N by the soil-plant system was not due to leaching but to denitrification. In the treatment (N+~*R) with labelled residue incorporation, the percent N recovery by plants was 16.2 percent, indicating the mineralisation of the residue applied.