Recovery of fertilizer and crop-residue 15N and effects on N fertilization in three cropping systems under mediterranean conditions

Our objective was to study the effects of crop residues on nutrient cycling and availability for a following wheat crop. The research program was conducted at three sites with differing climatic conditions: south Morocco (a wheat-wheat cropping system), central Morocco (sunflower-wheat), and the Atlas Mountains region (faba bean-wheat). Forty to 85 kg N ha-1 (9.764 at % excess 15N) were applied in three doses. The fertilizer-N recovery by the wheat in the first year was 37%, by sunflower 33%, and by faba bean 37%. At harvest, 22 to 43% of fertilizer N was residual in the 0- to 80-cm soil profile. Twenty-three to 42% of the applied N could not be accounted for. Recovery of the residual labelled fertilizer N by the subsequent wheat crop was 3.4 to 13% for the treatment with residue incorporation and 3.6 to 10% for the treatment without residue incorporation and for the treatment with residues only (T2) 9.6 to 15%. The third crop recovered 1.2 to 6.8% for the treatment with residue incorporation and 0.59 to 6.2% for the treatment without residue incorporation, and 2.9 to 6.2 in T2. (author)