Effect of biomass management strategies on carbon and nitrogen supply in legume and legume–grass mixtures under organic arable farming

Legumes can provide nitrogen through biological fixation, but retaining it in the soil for subsequent crop production must also be ensured. In this study, we assessed the effects of biomass management using forage legumes (Trifolium pratense L., Medicago sativa L.), as well as their mixtures with festulolium (× Festulolium), under organic arable farming conditions. Three biomass management treatments were applied: complete removal, partial removal with mulching, and full mulching The focus was on the mulch and root biomass and quality, decomposition dynamics, and changes in soil mineral nitrogen (SMN) and soil organic carbon (SOC) content. Results showed that the biomass C:N ratio was lowest in legumes, highest in festulolium, and intermediate in mixtures. Root biomass was greatest in legume–festulolium mixtures. Full mulching reduced the mulch C:N ratio, whereas the root C:N remained relatively stable and higher. Legume mulch (C:N ≤ 16) released 33–54% of N during the growing season, indicating that autumn SMN largely depended on root and litter decomposition. Mixtures maintained higher SMN than festulolium monocultures but less than pure legumes. The persistence of SMN until spring was influenced by both mulching practices and meteorological conditions. The greatest losses occurred when biomass was removed from the field or under full mulching. Partial removal with mulching reduced SMN losses and supported a more stable SOC.