Rotational leys in arable cropping systems: ley establishment, cropping system performance, and effects on soil fertility

Since the mid-20th century, European agriculture has become more specialised, resulting in increased labour productivity but also environmental challenges such as nutrient losses, high reliance on external inputs, and loss of soil organic matter, which contribute to reduced soil fertility. Reintroducing ley phases into arable crop rotations has been proposed as a strategy to improve soil fertility and reduce input dependency; however, their long-term effects in systems without manure inputs, as well as the potential of alternative establishment methods under changing climatic conditions, remain uncertain. This thesis evaluates the role of short-term leys in arable rotations using long-term experiments across Sweden, combined with field studies on clover autumn establishment of grass-clover leys in winter cereals and visual and image-based assessments of clover proportion. Rotational grass–legume ley increased cereal and oilseed brassica yields at low rates of nitrogen fertilisation. In winter wheat, less nitrogen fertiliser was required to achieve comparable grain nitrogen concentrations following grass–legume ley compared with without ley. Leys also enhanced topsoil carbon and nitrogen concentrations and potential nitrogen mineralisation, whilst bulk density was reduced at one site. Autumn establishment of clover in winter cereals was primarily influenced by management that affected light availability, with early cereal harvest increasing clover biomass, and red clover generally resulting in higher clover proportions and greater yields than white clover. Image-based methods for estimating clover proportion exhibited moderate accuracy, highlighting the need for additional calibration and further training before being useful in practice. Overall, short-term ley integration can contribute to a reduced reliance on nitrogen fertiliser and improved soil fertility, but the outcomes depend on management and site-specific factors.