Improving soil health, weed management and nitrogen dynamics by Trifolium subterraneum cover cropping

The low organic matter and nitrogen levels in the soils, as well as the high weed pressure, typical of Mediterranean agroecosystems, necessitate a valid and sustainable alternative management. The utilization of cover crops such as Trifolium subterraneum L. may represent an innovative and efficient option for low-input and organic agricultural systems. In a 3-year experiment, we evaluated the effect of T. subterraneum and spontaneous flora cover cropping, with or without burying dead mulch into the soil, on the quali-quantitative composition of the weed seed bank in an apricot orchard. Moreover, the bacteria Nitrosomonas europaea and Azotobacter vinelandii, involved in the soil N cycle, and the content of ammoniacal and nitric soil nitrogen were quantified. For the first time, we demonstrated that T. subterraneum cover cropping with the incorporation of dead mulches into the soil on the one hand reduced weed biodiversity and the seed bank size (- 70% compared to conventional management following the standard commercial practices), while, on the other hand, increased the amount of N. europaea (+ 109%), A. vinelandii (+ 145%), NH4+ (+ 137%) and NO3- (+ 478%) in the soil. This approach was therefore found to be a major improvement in low-input agriculture and organic farming, and it can be applied in Mediterranean orchards as an eco-friendly strategy with the aim of reducing synthetic herbicides for weed control and mineral nitrogen fertilizers as the sole source of nitrogen supply.