A field-scale assessment of the rotation benefits of pea and canola
van Kessel, C.
Producers and researchers have observed that higher cereal yields occur when oilseed and pulse crops are included in a cereal-intensive cropping system. A study was established in the spring of 1996 to compare the rotation benefit of a pulse crop (pea) with a second nonlegume broadleaf crop (canola) to succeeding cereal crops. It is anticipated that the benefit of pea in a crop rotation is due largely to non-N related factors, and that other broadleaf crops could provide the same benefits. Pea-wheat-barley, canola-wheat-barley, and wheat-wheat-barley rotations, were established in two field-scale (10 acre; each plot 30-m by 80-m) sites. The expression of rotation benefits from pea and canola to wheat were compared in different management units (shoulder, footslope, and level landform complexes). The seed yield of wheat sown after pea or canola was 14% higher than wheat sown after wheat at the St. Louis and Birch Hills sites. Furthermore, the N content of wheat seed was improved in the peawheat and canola-wheat rotations compared with the wheat-wheat rotation. Wheat leaf disease severity in the pea-wheat and canola-wheat rotations compared with the wheat-wheat rotation was reduced by 17% at St. Louis and 30% at Birch Hills, whereas, common root rot incidence did not differ among rotations. The reduction in leaf disease severity accounted for a portion of the yield advantage associated with wheat grown in the pea and canola rotations compared with the wheat-wheat rotation. The relationship between leaf disease severity and the yield advantage associated with crop rotation was strongest at Birch Hills. The unexplained portion of the rotation benefit at St. Louis was not associated with differences in weed infestations among the different crop rotations. Common root rot and weed infestations were similar among rotations, and there was no evidence to suggest that there were significant differences in soil N availability among rotations. It appears that pea and canola provide similar benefits to a succeeding wheat crop. Unaccountable reasons for the rotation effect on the seed yield of wheat among rotation and the spatial variation affecting growing conditions in the different rotations the complexity of field-scale processes associated with rotation benefit of broadleaf crops to succeeding cereal crops.
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