The potential of break crops for ley/arable rotations in organic agriculture
This thesis examines the potential of nine break crops (bean, carrot, swede, hemp, sugar beet, potato, lupin, oilseed rape and linola), against an oat control crop. Seven rotational field trails were carried out at five sites across the UK. The most profitable break crops in this study were carrot and potato in terms of direct economic return to the farmer. Mean annual returns were £5175 and £3668 respectively. Cereal yields following break crops were found to be more affected by the soil fertility before the break crops were planted, than the actual break crop. Studies on the nutrient concentration of break crops showed that by the second year of the experiment, over 50% of the break crops were deficient in either N, P or K, with N deficiency being most common. Subsequent cereal crops mostly had adequate nutrient concentrations. Break crop and cereal yields were more strongly correlated with soil nutrient concentrations at the start of the experiment that previous crop. Root crops showed a strong N response, sugar beet had a strong Mg response, linola, oilseed rape and oat had strong K responses, and wheat and barley yields were strongly influenced by soil N, P and Cu. In general soil nutrients decreased over the experiment as did pH and soil organic matter. In general there was an inverse relationship between the crops yield and the crop’s nutrient concentration, so as the yield of a crop increases, the concentration of nutrients in the plant matter, or quality, decrease. The break crops, hemp, linola and carrot generally had positive effects on reducing weed populations during growth and in the subsequent cereal crop compared with the control crop. In additional these break crops were pest- and disease-free during growth. Other break crops, such as bean, swede and oilseed rape were shown to suffer from many weed, pest or disease problems, which may limit their potential for inclusion in an organic rotation.