Chemical Composition and Decomposition of Litter in Signal Grass Pastures Fertilized with Increasing Nitrogen Doses or Intercropped with Calopo

Knowledge about the decomposition of litter in signal grass pastures is still limited, especially in pastures managed under deferred grazing. Thus, we aimed to evaluate the chemical composition, carbon/nitrogen (C/N) ratio, and decomposition rate of litter in signal grass (Urochloa decumbens cv. Basilisk) pastures not fertilized with N (U0), fertilized with 50 kg·N·ha−1 (U50), fertilized with 100 kg·N·ha−1 (U100), and intercropped with calopo (Calopogonium mucunoides Desv.) (UC), managed under deferred grazing at different incubation times for two experimental periods (2017–2018 and 2018–2019). Data were analyzed using a randomized block experimental design with four management systems and two blocks, each containing two replicates per treatment. Nitrogen sources increased the N concentrations in the litter before incubation. Nitrogen concentrations in the incubated litter were affected by the incubation times and periods, increasing over time, mainly for U50 and U100. U100 litter samples exhibited higher acid detergent insoluble nitrogen (ADIN) levels than the U0 litter samples only in period 2. Notably, the C/N ratio did not differ with the different management systems; however, it decreased with increasing incubation times and periods, with final values of 24:1 and 26:1 in periods 1 and 2, respectively. Overall, litter samples from pastures fertilized with chemical or biological N sources exhibited higher N concentrations, but their incubated litter samples exhibited higher ADIN concentrations. However, management systems did not affect C/N ratios and no differences in litter biomass decomposition were observed among the systems, possibly due to the grazing period occurring prior to litter sampling.