Preceding cultivation of grain legumes increases cereal yields under low nitrogen input conditions

The European Union (EU) has advised to increase the production of grain legumes, both to reduce EU dependency on soybean imports from the Americas and to reduce pollution from intensive cereal production. Several studies have indicated that preceding grain legume had a positive effect on the yields of subsequent cereals; this argument being often used to promote cultivation of grain legumes. However, no quantitative synthesis of the data has been performed on a global scale to estimate the relative increases in cereal yields arisen from cultivation of preceding grain legumes. Here, we performed a meta-analysis of 1181 yields of cereals cultivated in 15 countries. The results show that the yields of cereals cultivated after grain legumes were, on the average, + 29% higher than the yields of cereals cultivated after cereals. Our findings also show that the positive effect of grain legumes decreased with the nitrogen (N) fertilization applied to subsequent cereals, then became negligible when the mean N fertilization exceeded 150 kg N ha(-1). This threshold is often exceeded in European conventional cereal systems.