A LANDSCAPE-SCALE ASSESSMENT OF THE NITROGEN AND NON-NITROGEN ROTATION BENEFITS OF PEA

The inclusion of a pulse crop in a rotation often leads to an increase in seed yield of the succeeding cereal crop. Landscape-scale and smal l-plot studies were established in 1993 to assess the N and non-N rota tion benefit by pea (Pisum sativum L.) to the subsequent wheat (Tritic um aestivum L.) crop. In the second rotation phase, wheat seed yields were 982 kg ha(-1) greater and total N accumulation increased by 46 kg ha(-1) in the pea-wheat rotation. Reduced leaf disease severity and g rassy weed infestation were related to 91% of the yield advantage in t he pea-wheat rotation, the non-N rotation benefit. A 129 N kg ha(-1) i ncrease in the A value (soil N supplying power) was related to 9% of t he yield advantage in the pea-wheat rotation, the N benefit. In both r otations, seed yield was about 400 kg ha(-1) lower in the high-catchme nt footslopes than the low-catchment footslopes and shoulders. The lan dform effect on seed yield in the pea-wheat rotation was related to gr eater soil water and N content in the high-catchment footslopes. Incre ased grassy weed infestation In the high-catchment areas of the wheat- wheat rotation was related to lower seed yields in this same area. The rotation benefit of pea to wheat was 34% greater in the landscape-sca le vs. the small-plot study. Topographic variation interacted with fac tors responsible for the non-N rotation benefit. A landscape-scale ass essment of the rotation benefit from legumes can be used to develop si te-specific management strategies that consider the effect of crop rot ation.