The decomposition and nutrient release dynamics of mixed cover crops in a no‐till row crop rotation

Abstract

Impacts of cover crop mixtures on essential nutrient availability after termination are not well understood in the Mid‐South. This study's goal was to evaluate cover crop biomass degradation and nutrient availability in soils. Experiments were conducted at the Macon Ridge Research Station (MRRS) and Dean Lee Research Station (DLRS) in Louisiana. At MRRS, treatments included seven cover crop (including mono‐ and polycultures of legumes, grasses, and a brassica) and a fallow as the main plot, with two N rates (0 and 179 kg N ha⁻¹) as the subplot. DLRS used four cover crop treatments. Cover crop biomass was collected at termination in mid‐February and placed in nylon mesh bags on the soil surface. Soil samples and nylon bags were collected at 0, 1, 2, 3, 4, 6, and 8 weeks post‐termination and used to assess biomass degradation and nutrient release over time. Polyculture cover crop mixes tended to produce more biomass and N assimilation. The optimum timing of inorganic N availability was 6 weeks after cover crop termination, which resulted in greater soil NO₃⁻‐N, allowing for synchronous release of N to meet the main crop N demand in early spring. Soil P, K, and S were not significantly different among cover crop treatments. A mix of black oats (Avena strigosa) + crimson clover (CC, Trifolium incarnatum) + radish (RD, Raphanus sativus) showed the most rapid N degradation rate while CC + hairy vetch (Vicia villosa Roth) + RD had the greatest N released from biomass. Findings emphasized the importance of selecting proper cover crop mixtures and termination timing to improve nutrient cycling in no‐till systems.