Pedoclimatic, knowledge and management factors drive European soybean and faba bean yields

The low usage of grain legumes in European cropping systems is often attributed to yield gaps due to limiting pedoclimatic conditions, sub-optimal management practices, and farmers’ limited experience and knowledge in growing these crops. The relative contributions of these factors to current grain legume yield gaps at European scale and, in particular, the difference between yields achieved by experienced farmers and those achieved by novices remain unknown. We therefore explored the relationship between yields and these different factors, to identify areas where farmers require more support to close the yield gaps in grain legume production. To this purpose, we conducted a large-scale online farmer survey in nine European countries with a focus on soybean and faba bean. For both crops, classification and regression tree analysis identified country of production as the primary explanatory variable of yield variation and confirmed the hypothesis that greater experience and knowledge is associated with higher yields. However, the effect of several factors differed between the crops, showing the need for legume-specific strategies. Experience and knowledge were particularly important for soybean, although also relevant for faba bean in low-yielding environments. Other important factors identified to determine yield for soybean included farm specialization, agroclimatic zone, the number of years growing grain legumes and the size of farmland, while for faba bean these important factors were pest management and perceived soil fertility. Farmers highlighted drought, weed infestation, and soil characteristics as having critical impacts on yields for both crops, as well as inoculation and irrigation for soybean. Both soybean and faba bean growers emphasized the need for more information on plant protection and cultivar selection. The results indicate the potential to increase legume yields by supporting farmers in the first years of growing grain legumes, especially for crops that have a shorter history in Europe such as soybean.