Stocking Rate and Nitrogen Fertilization Affect Root Decomposition of Elephantgrass

Abstract

Roots are an important component controlling grassland sustainability. They can act as a C sink of atmospheric CO2 and supply essential nutrients for plant growth. Pasture management strategies intended to increase forage and animal production can also affect root biomass, root composition, and root decomposition. This 2‐yr study evaluated the effects of N fertilization and stocking rate (SR) on root decomposition and root chemical composition of grazed elephantgrass (Pennisetum purpureum Schum. ‘381’) pastures. Treatments consisted of a factorial combination of three SR (2.0, 3.9, and 5.8 animal unit [AU] ha−1, 1 AU = 450 kg body weight) and three N levels (0, 150, and 300 kg N ha−1 yr−1). Greater turnover rates were observed in Year 2 (k = 0.00215 g g−1 d−1) than Year 1 (k = 0.00178 g g−1 d−1). Increasing SR increased root decomposition linearly (P = 0.05) at 0 kg N ha−1; nevertheless, when N was applied at 300 kg N ha−1, root decomposition decreased (P = 0.003). Nitrogen fertilization reduced root C to N ratio and increased root N and root acid detergent insoluble nitrogen (ADIN) concentrations in Year 1, but no effects were observed in Year 2. Root N disappearance followed a negative single exponential model and increased with increasing levels of N fertilization. Pasture management practices such as fertilization and grazing management can alter the root quality and turnover; thus, development of strategies to manage belowground decomposition is a key to long‐term grassland sustainability.