Organic minimum tillage systems based on intensification of legume cover cropping: agronomic and phytopathological aspects

Yields in organic farming have been stagnating, widening the gap with conventional systems. Thus, there is the need to reconsider traditional organic crop rotations and adopt innovative strategies that will maximize nutrient supply, weed suppression, and reduce disease risks. Overwintering legume cover crops offer potential solutions, but their role in nutrient cycling, weed management and pathogen dynamics needs to be clarified. In two multi-factorial field trials, we examined organic farming systems using no-till or minimal tillage with a 2-year rotation of winter-hardy legumes as cover crops, maize and a wheat/pea mixture. The risks of soil-borne pathogens and their transmission to subsequent crops were also assessed. The effects of the following factors were investigated: (a) cover crop type: winter vetch and crimson clover, (b) date of cover crop kill, (c) sowing technique: no-till or shallow tillage, and (d) use of cover crop biomass: green manure or mulch vs. harvest. The strong weed suppression of legumes allowed for herbicide-free implementation of minimum tillage and no-tillage systems, while their substantial nitrogen contributions supported the high maize yields. It was also possible to harvest the cover crop biomass before maize sowing instead of using it as mulch or green manure, without significantly affecting maize yields. Infestations with seed and root rot pathogens were generally low, and there was no risk of pathogen accumulation or transfer to subsequent crops. To our knowledge, this is the first systemic assessment of agronomic and phytopathological aspects in a rotation involving winter-hardy legumes, maize and a wheat/pea mixture under differential tillage practices. Taken together, our results demonstrate that, with proper management, legume-intensive rotations can maximize agronomic benefits, minimize phytopathological risks, and enhance productivity and sustainability in both organic and conventional farming, while contributing to a reduction of yield gap between systems.