Nitrogen and Grazing Affect Napier Grass Leaf Litter Biomass and Decomposition

Abstract

Core Ideas Stocking rate reduced litter deposition. Management intensity affected litter decomposition. Nitrogen fertilization did not change litter deposition in grazed pastures. Stocking rate (SR) and N fertilization are important management practices that may alter nutrient cycling. We tested three SR [2, 3.9, and 5.8 animal units (AU) ha−1; 1 AU = 450 kg BW] and three N rates (0, 150, and 300 kg N ha−1yr−1) on litter mass, chemical composition, and decomposition in a napier grass (Pennisetum purpureum Schum.) pasture. Fertilizer rate did not change (P = 0.4658) litter accumulation but decomposition after 254 d was greatest (P ≤ 0.05) at the greatest management intensity. Litter mass was affected by a year × month interaction (P ≤ 0.01), but in general the greatest litter mass occurred (P ≤ 0.05) at the end of the growing season, and carried over to beginning of the next growing season. There was a SR × year interaction for litter mass. At 3.9 and 5.8 AU ha−1, litter mass was greater in 2009 than in 2010. Visual observation indicated that in 2010 at the 3.9 and 5.8 AU ha−1 SR, the napier grass pasture was degrading, generating less biomass and consequently less litter than in 2009. In general, litter C/N ratio was above 30. There was no effect of SR (P = 0.2684) or SR interaction with year (P = 0.1558) on litter N concentration, with an average of 14 g N kg−1. Our results indicated that napier grass management affect litter mass and C/N ratio. This has implications for litter decomposition and nutrient dynamics in these pastures.