Nitrogen fertilization increased grass litter decomposition in a tropical agroforestry system

Litter decomposition and livestock excreta are two important sources for replenishing nutrients in the soil of the pastures, and their decomposition rates are affected by their quality, management practices, forage productivity, and biotic and abiotic factors. The objective of this research was to assess the effects of escalating levels of N fertilization (0, 100, 200, and 400 kg N ha⁻¹ yr⁻¹) on litter and fecal decomposition in an agroforestry system comprising palisadegrass [Urochloa brizantha (Hochst. Ex A. Rich.) Stapf. cv. Marandu] intercropped with hybrid eucalyptus trees [Eucalyptus urophylla × Eucalyptus tereticornis], in a two-year field trial. The experiment was set in a randomized complete block design with four treatments and three repetitions. Litter (0, 4, 8, 16, 32, 64, 128, and 256 days) and cattle excrement samples (0, 4, 8, 16, 32, 64, and 128 days) were incubated on the ground. For forage litter samples, the interaction between N fertilization × year was observed for the decomposition rate (k) of DM (P = 0.0014) and OM (P = 0.0094). The greatest litter OM disappearance was observed at 400 kg N fertilization ha⁻¹ year⁻¹ (651 g kg⁻¹ DM at 256 days). The interaction between nitrogen fertilizer rate × incubation time, or the isolated effect of the treatment was not observed on fecal decomposition (P > 0.05). Higher levels of N fertilization associated with the rainy period resulted in faster decomposition of palisadegrass litter, however, it did not show to have a strong influence on the excreta decomposition in this agroforestry system.