Uncovering Legume Soil Fatigue for Sustainable Expansion of European Grain Legume Cultivation

Over the past decades, efforts have been made to promote the cultivation of legumes, especially grain legumes, to reduce the use of mineral N fertilisers, increase biodiversity, reduce dependence on imported feed proteins and improve soil biological properties and humus content. However, grain legumes are still not widely grown. One of the main reasons is "legume fatigue", which limits the expansion of legume cultivation in many European environments. The exact causes of legume fatigue are not known, although soil-borne diseases interacting with abiotic factors are thought to play a key role. Recent results suggest that the balance between pathogen load and soil suppressiveness, rather than pathogen load alone, is critical. In several farms or regions legume fatigue is not reported to be a problem, while in others it severely limits legume production. The reasons for this variation are not fully understood, but identification of the causes is urgent, but only possible in a collaborative project covering several different environments and including multiple assessments of biotic and abiotic factors. A network of farms and long-term experiments will be established across a transect from southern to northern Europe (Italy, Germany, Luxembourg, and Norway), with the purpose of identifying the main factors determining legume fatigue in a variety of European environments. These may be biodiversity parameters or the presence of specific functional groups of the soil or endophytic microbiome. The project will focus on developing easy to implement indicators to assess the risk of legume fatigue and propose agronomic measures to prevent or reduce legume fatigue (subject to verification in subsequent research). Thus, the project aims to provide a fundament for further targeted research.

Over the past decades, countless efforts have been made to promote the cultivation of legumes, especially grain legumes, to reduce the use of mineral N fertilisers, increase biodiversity, reduce dependence on imported feed proteins and improve soil biological properties and humus content. However, grain legumes are still not widely grown. One of the main reasons is "legume fatigue", which limits the expansion of legume cultivation in many European environments. The exact causes of legume fatigue are not known, although soil-borne diseases interacting with abiotic factors are thought to play a key role. Recent results suggest that the balance between pathogen load and soil suppressiveness, rather than pathogen load alone, is critical. In several farms and/or regions legume fatigue is not reported to be a problem, while in others it severely limits legume production. The reasons for this variation are not fully understood, but identification of the causes is urgent, but only possible in a collaborative project covering several different environments and including multiple assessments of biotic and abiotic factors. A network of farms and long-term experiments will be established with the purpose of identify main factors determining legume fatigue. The network will be established across a transect from southern to northern Europe (Italy, Germany, Luxembourg and Norway). Norway will be represented by NIBIO and NMBU. Their main contribution will be i) to identify Norwegian farms to participate in the farm network (by doing a survey among a farmers in the main regions for protein crop cultivation) and ii) perform field assessments and sampling of plant and soil on selected farms. Data collected by all partners in the farm network will be used to identify main factors determining legume fatigue and deliver a reliable set of indicators for legume fatigue as well as disease suppressive soils and connect these indicators to the management practices that likely led to them.