The effect of crop rotation and sheep grazing management on plant production and soil C and N stocks in a long-term integrated crop-livestock system in Southern Brazil

Integrated crop-livestock systems (ICLS) conducted under no-tillage have been shown to favour the accumulation of carbon (C) and nitrogen (N) in soil. In that systems, however, C and N accumulation in soil might depend on pasture management and the type of crop rotation used. The objective of this study was to evaluate the impact of two stocking methods (continuous and rotational) and two sheep grazing intensities (moderate and low) on winter pasture and the effect of summer crop rotation (soybean and/or maize) on crop yield and C and N stocks in an Acrisol after 14-yr under experimental conditions. The evaluated ICLS was set up for grain yield in the summer crop phase and for sheep meat production in the winter pasture phase. Pasture production, soybean and corn yield were evaluated throughout the experimental period. After 14-yr, the soil was sampled at the 0–5, 5–10, 10–20 and 20−30 cm layers to evaluate the content and stock of C and N. Higher C and N contents in soil superficial layers (0–5 and 5–10 cm) were observed under low grazing intensity in winter and soybean monoculture in summer. The C and N stocks in 0−30 cm soil layer ranged between 39 and 45 Mg C ha⁻¹ and 4 and 5 Mg N ha⁻¹, respectively. C and N stocks in the soil were significantly related to N added through the residues of pasture and summer crop. This positive relationship is possibly explained by the higher efficiency of microbes in using crop residues enriched in N with posterior stabilization of microbial residues through organo-mineral association in the soil. The higher content and stocks of C and N associated with low intensity grazing favoured a higher maize yield (40%) compared to moderate grazing intensity in the 2015/2016 season. According to our results, the accumulation of C and N in the soil under ICLS involving low grazing intensity in the winter and soybean monoculture in the summer was related to the N added/recycled by the soybean and by the hibernal pasture.