Magnitude and farm-economic value of grain legume pre-crop benefits in Europe: A review

Grain legume production offers multiple environmental benefits and can enhance sustainability of European farming, but their production area is declining constantly. Grain legume competitiveness is frequently constrained by lower gross margins compared to agronomically suitable cropping alternatives, but it can be improved by appreciating their ability to increase yield of subsequent crop(s) and, potentially, to reduce input requirements (fertiliser, biocide, tillage). Information on the magnitude of grain legume pre-crop effects is diverse and has not been synthesised for European agriculture. This paper reviews research on pre-crop benefits to yield and input requirements of subsequent crops, and the farm-economic profitability of grain legumes in European cropping systems. This includes an analysis of the magnitude of pre-crop benefits to cereal yields measured in 29 experiments in Europe; and 19 studies on grain legume gross margins ranging from crop to cropping system level are assessed. In the available studies, yield benefits of legumes to subsequent crops are highest under low nitrogen fertilisation to subsequent crops and fertilisation can be reduced by 60 kg N ha−1 on average under maintenance of acceptable yields. With the aim at maximising yield potential, nitrogen fertilisation following grain legumes can be reduced by 23-31 kg ha−1, and cereal yields are mostly 0.5-1.6 Mg ha−1 higher than after cereal pre-crops. With adequate estimates of pre-crop benefits, gross margins of full crop rotations can better assess grain legume competitiveness. In the studies reviewed, 35 of 53 modelled crop rotations with grain legumes were competitive with comparable non-legume rotations. Grain legume rotations were more competitive under conservation tillage systems if gross margin calculations accounted for cost savings arising from adjusted machinery requirements. In conclusion, grain legume pre-crop value is a crucial component of their farm-economic profitability in European cropping systems, but further experimental research is required to ascertain its magnitude. Expanding profitability measures to consider pre-crop effects substantially increases the number of situations where grain legumes can compete with cereals, and has a small positive effect on their competitiveness with alternative break crops. Besides a better consideration of the pre-crop value, further genetic and agronomic improvement in legume cropping, supportive market development, and policy support are required if Europe is to utilise environmental benefits of legumes and increase the sustainability of its farming.