Response of three cereal crops in continuous arable or ley-arable rotations to fertiliser nitrogen and soil nitrogen at Rothamsted's Woburn Ley-arable experiment

The concept of improving soil fertility by ley-arable farming, developed in the 1930s in England, was practised on many “mixed” farms that had both arable crops and permanent grass. The practice declined from the 1960s as farms became predominantly arable or grassland. However, there is increasing interest in including leys in arable farming to fix carbon from carbon dioxide in the atmosphere in soil organic matter (SOM). For example, in the United Kingdom a project “Grass and herbal leys in farm network” was launched in 2018 (adas.uk, 2020) and in the European Union (EU) farmers are now required to grow a wider range of crops (ec. europa.eu, 2020.
The Woburn Ley-arable experiment started in 1938 has compared six rotations, two with 3-yr leys, two with 8-yr leys and two with continuous arable crops on the yields of two cereal test crops. The effect of these rotations on SOM is given elsewhere (Johnston et al., 2017). Here we give the yields of both test crops in each of the six rotations for 21 years starting in 1981. We discuss the response to four levels of applied fertiliser nitrogen (N), the effect of rotation, the level of SOM and the availability of soil N. Where no fertiliser N was added, crop yields increased as % N in soil increased, but, with sufficient fertiliser N there was little benefit from the extra N in the soil. Yields of winter wheat were larger after the 3-year grass ley than in the all-arable rotations and larger again following the grass/clover ley. Less fertiliser N was needed to achieve the yields after the leys than in the all-arable rotations. Yields of the second cereal crop following 3- or 8-yr leys were also larger than those in all-arable rotations but there was no difference between the leys. However, the extra N available from the leys and the increases in yield were modest. If leys are to be introduced into mainly arable farming systems, they may need to be subsidised to make them financially viable.