Landscape-scale controls on the availability of pea-residue nitrogen for the subsequent wheat crop
van Kessel, C.
Increased N uptake is a major mechanism responsible for the rotation benefit of a pulse crop to a succeeding cereal crop. The objective of our study was to determine the sources of N in pea-wheat vs. wheat-wheat rotation using a landscape-scale research approach. In 1993, a pea-wheat and wheat-wheat rotation were established in adjacent 1 ha sampling grids. Measurements were conducted in the second phase of the rotation. At the time of sowing in 1994, mineral N in pea-wheat rotation was 7 kg ha-1 greater than in the wheat-wheat rotation. Mean seed yield was 68% greater in the pea-wheat vs. wheat-wheat rotation-a 940 kg ha- r rotation benefit. A 14% reduction in seed yield within the footslopes of the pea-wheat rotation was related to excessive resource availability and lodging. Compared to the wheat-wheat rotation, an additional 40 kg ha-1 of N yield in wheat residue and seed was measured in the pea-wheat rotation. A higher residue plus seed N yield in the pea-wheat rotation occurred from the soil N pool, since only 7 kg ha-1 was derived from pea residue N returned to the soil in 1993, and mean N derived from fertilizer N was 11 kg ha-1 and did not differ between the rotations. This extra soil N uptake was attributed, in part, to lower root and leaf diseases prevalence in the pea-wheat rotation. From our results it was estimated that =15% of the rotation benefit was related directed to the uptake of mineralized pea residue N . Processes indirectly increasing N availability in the pea-wheat rotation were thought to be the important mechanisms contributing to the remainder of the rotation benefit.
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