Estoques e frações de carbono e nitrogênio do solo sob plantio direto com plantas de cobertura em condições subtropicais

Abstract

This study aimed to evaluate soil carbon (C) and nitrogen (N) stocks and fractions, as well as management indices reflecting C quantity and quality, in maize production systems under No-Till Farming (NTF), cultivated in succession to different cover crops and under varying mineral nitrogen fertilization rates in subtropical conditions. The long-term study, with samples collected up to 100 cm, demonstrated that the adoption of cover crops (CCs), regardless of the functional group, promoted significant increments in C and N stocks compared to fallow. Grasses excelled in high C accumulation in surface layers and a higher C/N ratio. Legumes, in turn, contributed significantly to increased total N and a lower C/N ratio, resulting in a higher proportion of labile C, while mixtures combined structural and chemical advantages. Depth analysis evidenced that labile C (POC) concentrates on the surface (0–5 cm), and mineral-associated C (MAC) predominates in subsurface layers. High-dose mineral N fertilization ($180 \text{ kg } \text{ha}^{-1}$) favored POC accumulation in grass systems due to greater biomass production but reduced C lability and, in some cases, C stocks in legume systems, possibly due to accelerated mineralization. Integrated indices (TCI, CQI, and CMI) confirmed the superior performance of all systems with CCs. It is concluded that the diversification of cover crops in NTF, associated with balanced nitrogen fertilization management, is an efficient strategy to improve soil fertility and quality, promote C sequestration, and ensure agricultural sustainability.