Legume Proportion and Litter Deposition Rate in Signal Grass–Forage Peanut Mixed Pastures at Varying Planting Spacings

Mixed legume–grass pastures may enhance nitrogen recycling via litter and excreta compared to unfertilized grass monocultures. This study evaluated litter biomass, litter deposition rate, and the chemical and isotopic composition of Urochloa decumbens litter in monoculture and mixed pasture intercropped with Arachis pintoi cv. Belmonte at five planting spacings (0.40, 0.50, 0.60, 0.70, and 0.80 m) in a Ferralsol. Additionally, isotopic analysis of sheep feces under grazing was conducted across the dry season. The experiment was conducted according to a split-plot scheme, with spacings in the plots and the periods or years in the subplots, in a randomized block design, with four replications. Litter biomass was not significantly influenced by planting spacing; however, the litter deposition rate was substantially greater in mixed pastures, reaching up to 77.2 kg ha −1 day −1 in the second year. Isotopic analysis revealed that up to 39% of the litter carbon was derived from C3 plants ( Arachis pintoi ), while nitrogen concentration ranged from 8.3 g kg −1 in monoculture to 12.9 g kg −1 at 0.40 m spacing. Spatial arrangement was critical for optimizing nutrients dynamic. Narrower planting spacings (0.40–0.50 m) increased the proportion of Arachis pintoi and enhanced litter deposition rates, improving nitrogen inputs and cycling within mixed Urochloa decumbens .