Deposition and Decomposition of Signal Grass Pasture Litter under Varying Nitrogen Fertilizer and Stocking Rates

Increasing pressure on land used for animal production demands more efficient production systems. Soil nutrients required for plant growth are usually the limiting factor in pasture productivity in the tropics. Thus, understanding nutrient cycling in grasslands is crucial to maintaining pasture sustainability where litter deposition and decomposition are important components of the nutrient cycle. This research evaluated the effects of stocking rate [SR; 2.0, 3.9, and 5.8 animal units (AU) ha(-1); 1 AU = 450 kg cattle live weight] and N fertilization (0, 150, and 300 kg N ha(-1) yr(-1)) on litter mass and chemical composition in signal grass (Brachiaria decumbens Stapf.) pastures during two grazing seasons [2009 and 2010; 1709 and 2103 kg organic matter (OM) ha(-1), respectively]. In 2009, the highest SR treatments (3.9 and 5.8 AU ha(-1)) had less litter mass accumulation (2093 and 2205 kg OM ha(-1), respectively) than the lowest SR (2750 kg OM ha(-1)). Litter deposition rate was similar among SR treatments and between years, and averaged 26 kg OM ha(-1) d(-1). Litter N concentration increased with increasing N fertilization only in the second year (8.6 vs. 11.7 g kg(-1) at 0 and 300 kg N ha(-1), respectively). Nitrogen fertilization reduced litter C/N ratio for the range of SR tested, but the reduction was more pronounced for the lowest SR (53.1 vs. 29.1 for 0 and 300 kg N ha(-1), respectively). Nitrogen fertilization mitigated the negative effect of increasing SR on litter mass deposition and chemical composition by stimulating plant regrowth.