Spatial pattern of tree litter decomposition and soil C and N stocks in a silvopastoral system in the Cerrado biome

The use of Eucalyptus spp. in silvopastoral systems can impact carbon (C) sink and nutrient cycling through variations in traits like nutrient uptake, canopy structure, and litter quality. This study aimed to evaluate litter dynamics, CO₂ efflux, and soil C and N stocks in a silvopastoral system with low fertilizer inputs, comparing the results with nominal pasture and native vegetation in the Brazilian Cerrado. Three sampling points were evaluated in the silvopastoral system (SPS), one between the trees of a double row of eucalyptus (P1), and two points in the alleys, 2.5 (P2) and 7 meters (P3) from the row of trees. Litter from the eucalyptus was collected monthly over one year using litter traps, while decomposition rate was estimated by evaluating the amount remaining in the litterbags over the same period. Soil samples were collected at depths of up to 50 cm to assess the soil density and C and N stocks. At P1, the average annual litter deposition was 5.85 Mg ha^-1 yr^-1, while at P2 and P3 was 5.20 and 4.17 Mg ha^-1 yr^-1, respectively. The decomposition rate was similar between P1 (0.00309 g g^-1 day^-1) and P3 (0.00342 g g^-1 day^-1), and lower at P2 (0.00248 g g^-1 day^-1), showing a half-life for decomposition 224, 203 and 279 days for P1, P3 and P2, respectively. The litter input helped maintain the levels of nutrients in the silvopastoral system, since after the first five years of growth, no chemical fertilizers were applied. In silvopastoral system, the highest CO₂ efflux was seen in January at P1 (6.798 μmol m^-2 s^-1) and P2 (3.994 μmol m^-2 s^-1). The arrangement and spacing of the rows of the tree component affected the dynamics of litter decomposition, since the higher soil moisture near the trees accelerated the decomposition and increased the CO₂ efflux. The soil C and N stocks in the 0-50 cm layer were higher in NV (115.4 Mg ha^-1 and 11.3 Mg ha^-1), and similar between NP (92.4 Mg ha^-1 and 8.7 Mg ha^-1) and SPS (89.9 Mg ha^-1 and 8.9 Mg ha^-1), showing the importance of litter decomposition to maintaining these stocks, once there was a lack of management practices in SPS during the production cycle. Further research is needed under controlled fertilization management and different edaphoclimatic conditions to better understand the potential of eucalyptus to enhance soil C accumulation and nutrient cycling within the silvopastoral systems.