Abstract
Besides its bioenergy potential, perennial grasses can also have positive impacts on soil quality. However, responses of soil organic carbon (SOC) and total nitrogen (TN) depend on multiple factors, including grass species selection and N and P addition. We investigated the effect of four N and P fertility treatments (control = 0 kg N + 0 kg P ha(-1) [N0P0]; 100 kg N + 0 kg P ha(-1) [N1P0]; 0 kg N + 100 kg P ha(-1) [N0P1]; 100 kg N + 100 kg P ha(-1) [N1P1] applied annually] across 9 yr in Uruguay on soil nutrient balances, C and N pools, and biomass yields of elephantgrass (EG) (Pennisetum purpureum Schum.), giant reed (GR) (Arundo donax L.), and switchgrass (SW) (Panicum virgatum L.). Across years, EG had the highest biomass yield, followed by GR and SW (18.9, 16.3, and 14.1 Mg ha(-1) yr(-1), respectively). Across species, aboveground biomass increased by 46% with N addition. Yield response to P fertilization was lower (+11%). Elephantgrass had the highest N and P negative balance. Soil organic C and TN concentration were affected by species but not by fertilizer treatments. Giant reed had the highest SOC content gain in the first 0-40 cm (540 kg C ha(-) yr(-1)), and was the only species maintaining TN content from the beginning of the study. Giant reed could be an excellent option as a bioenergy crop due to its high aboveground biomass production, and its positive impacts on SOC and TN pools.