The effect of conversion strategy on the yield of the first organic crop

Abstract It is common practice for legume-containing leys to be used to improve soil fertility in the 2-year conversion period from conventional to organic production. While in-conversion land may be grazed, it is effectively out of production in stockless farming systems, potentially resulting in a reduction in income and pressure on cash flow. The objective of this work was to investigate alternative conversion strategies for stockless farming systems that would provide some economic return during the conversion period. To meet this objective, the effects of seven conversion strategies on a subsequent organic winter wheat crop were investigated on a sandy loam and a sandy clay soil. The strategies were: (1) 2-years’ red clover–ryegrass green manure; (2) 2-years’ hairy vetch green manure; (3) red clover for seed production then a red clover–ryegrass green manure; (4) spring wheat undersown with red clover, then a red clover green manure; (5) spring wheat, then winter beans; (6) spring oats, then winter beans; (7) spring wheat undersown with red clover, then a barley–pea intercrop. Conversion strategies had a significant impact on organic wheat yield, which ranged from 2.8 to 5.3 t ha−1. However, differences in yield were not directly related to the effect of conversion strategy on nitrogen availability or weed suppression, but to their impact on soil structure. Establishment was the main determinant of wheat yield, and 89% of the variation in establishment was explained by differences in soil structure and texture. When comparing organic cropping on different soil textures, the ease of cultivation and seedbed preparation on the sandy loam was more important than the additional nutrient retention of the sandy clay.