The ability to maintain crop yield and quality in systems based on nitrogen (N) fixed by legumes rather than from synthetic N fertilisers is fundamental to the long-term viability of organic farming. This paper reports crop yield and nitrogen uptake parameters for the first spring oat crop after grass/clover ley in organically managed ley/arable rotations to indicate the amount of fertility built-up during the ley period. The trial site, at Tulloch in North East Scotland, underwent two complete cycles of 6-year ley/arable rotations with different lengths of grazed ley (3 or 4 years). Trials were sufficiently replicated so that each course of the rotation was present in every year. The rotation containing 3 years of ley was also compared with a similar rotation at a nearby site (Woodside) with lower rainfall and soil fertility over one and a half rotational cycles. Grain yields were consistently higher at Tulloch (5.1 tha -1 compared with 4.5 tha -1 at Woodside) and were unaffected by the length of ley. However, grain N percentage was higher following the 4-year ley (1.38% compared with 1.30% following the 3-year ley). While yields were maintained between the first and second cycles of all the rotations, grain N percentage declined. Annual grain yields of the organically grown oats at Tulloch were not significantly different from National List/Recommended List yields in NE Scotland for oats receiving 100 kg N ha -1. Results suggest that these particular rotation designs were suitable for maintaining acceptable grain yields under organic management conditions.
