nitrogen and non-nitrogen rotation benefits of pea to succeeding crops

The inclusion of a pulse crop in a rotation often leads to greater seed yields in the succeeding cereal crop. Two rotations were established at three sites in 1993 to examine the N and non-N rotation benefits of pea (Pisum sativum L.) to the subsequent wheat (Triticum aestivum L.) then oilseed crops. Wheat seed yield was 43% greater (rotation benefit) when preceded by pea rather than wheat, a consistent response among sites. Six to fourteen kg ha −1 of the extra 27 kg ha −1 of N accumulated by wheat in the pea–wheat rotation was derived from the additional N derived from pea residue. The additional soil N availability in the pea–wheat rotation, as indicated by the A-value, explained 8% of the rotation effect on seed yield (N benefit). The remaining 92% of the yield advantage in the pea–wheat rotation was attributed to non-N rotation benefit. The yield of the oilseed crop following the pea–wheat phase of the rotation did not differ from that following the wheat–wheat phase. The influence of growing conditions and cropping history on the magnitude of the N to non-N rotation benefits, and the contribution of different non-N effects, should be investigated further. Key words: Rotation benefit, pea, wheat, residue N, non-N benefit