Carbon patterns and soil quality in fragile soils under sustainable soil management in organic systems of Southeastern Brazil: Short-term assessment

ABSTRACT Adopting conservationist soil use and management practices, such as the no-tillage system and cover crops associated with organic agriculture, can improve the quality of fragile soils. This study aimed to evaluate changes in soil fertility and the accumulation of soil organic matter and its fractions in sandy-textured soils under a 3-year no-tillage system in Seropédica, Rio de Janeiro. The experimental design was in randomized blocks, with three replications, in a 2 × 6 split plot scheme, with two planting systems distributed in the plots (no-tillage and conventional-tillage) and six cover plants distributed in isolated and intercropped subplots (Millet - Pennisetum glaucum; Crotalaria - Crotalaria juncea and Jack beans - Canavalia ensiformis; cocktailsformed by mixing 100 % of the seeds of the recommended cover crops; consortium formed by combining 50 % of the plant seeds recommended coverage and spontaneous plants maintained in the fallow area). The contents and stocks of total soil organic carbon, particulate organic carbon, mineral-associated organic carbon, soil organic carbon free light fraction, and soil fertility properties were measured in layers 0.00-0.05, 0.05-0.10, and 0.10-0.20 m in 2019 and 2022. Our findings suggest that cover crop incorporation in the conventional-tillage favored greater nutrient availability compared to the no-tillage. Conversely, the no-tillage system demonstrated promising potential for soil carbon sequestration, especially within the more stable fractions (mineral-associated organic carbon), in organic vegetable production. The three-year period was insufficient to promote an increase in labile soil organic carbon, particularly particulate organic carbon (POC) and the free light fraction (FLL). Notably, POC decreased in the 0.05-0.10 and 0.10-0.20 m layers under both no-tillage (-37 % and -48 %) and conventional tillage (-5 % and -38 %) systems.