Towards an integrated understanding of legume soil fatigue

Grain legumes play an essential role in human and animal nutrition, representing a rich source of high-quality plant-based protein. They significantly contribute to sustainable agriculture, particularly due to (i) their ability for biological nitrogen fixation, which allows a significant reduction in synthetic fertilizer utilization and (ii) their intense rooting, which leads to improvements in soil structure. These beneficial properties of grain legumes qualify them as “future crops”, and political measures on national and European levels point towards a distinct increase in their cultivation. Nevertheless, a certain set of biotic and abiotic factors could significantly impede legume growth and compromise their grain yields. Farmers and researchers are discussing what they call e.g. soil fatigue, soil sickness, legume yield depression syndrome, clover fatigue or root rot complex without necessarily meaning precisely the same. Despite numerous reports in scientific journals and public media, the concepts are not clearly delineated from each other although they show different foci. Resulting from this, there is a lack of common perception of the issue. The authors suggest using the terminology legume soil fatigue when a phenomenon of a gradual or sudden decline in legume productivity and overall root health resulting from repeated cultivation of legumes at the same site or in the same soil is observed and reported. This opinion article aims to summarize existing concepts addressing the topic of legume soil fatigue, compare them and integrate their approaches to finally suggest a broad, encompassing perception for the phenomenon of legume soil fatigue. The proposed perception may present an umbrella to address future research needs for sustainable legume cultivation. Similarly, accurately diagnosing unhealthy plants in the field is virtually impossible without a commonly accepted perception of the multi-cause legume soil fatigue. Lastly, the article aims to raise awareness about legume soil fatigue and its multicausal character.