Cover crop dynamics in organic systems in Southeastern Brazil: the role of season and soil management

Abstract This study evaluated the effects of seasonality, soil management (no-till and conventional tillage), and different cover crop combinations on (i) aboveground dry biomass production, nutrient content, and accumulation; (ii) residue decomposition; and (iii) nutrient release (N, P, K). The experiment was conducted in summer and winter at the certified organic farm Sítio do Sol, Seropédica, Rio de Janeiro, Brazil. A randomized complete block design with three replicates was used in a 2 × 6 split-plot scheme. Main plots were two soil management systems: no-till (NT) and conventional tillage (CT). Subplots included six cover crop treatments: millet (M) ( Pennisetum glaucum ), sunn hemp (CJ) ( Crotalaria juncea ), jack bean (JB) ( Canavalia ensiformis ), two mixtures of these three cover crops (C1 = 100% seeding rate; C2 = 50% for each cover crop), and spontaneous vegetation (SP). Aboveground dry biomass production and nutrient accumulation were higher in summer, especially for CJ, C1, and C2, with CJ reaching 10.32 Mg ha⁻ 1 and 250.32 kg N ha⁻ 1 . Winter crops had higher nutrient concentrations (g kg⁻ 1 ), contributing to a lower C/N ratio and slower decomposition. Decomposition was faster in summer, with the quickest breakdown in C1 (k = 0.0193 g g⁻ 1 ; T₁/₂ = 36 days). Nutrient release patterns were generally consistent across seasons, with K having the shortest half-life (16 days in summer; 15 in winter). CJ is recommended for summer due to its aboveground dry biomass and nutrient contributions, while C1 and C2 mixtures are more effective in winter. The results highlight the seasonal variability in cover crop performance and the need for species-specific strategies in organic no-till systems.