Intensification enhances litter carbon and nitrogen decomposition dynamics in subtropical grazinglands

Abstract

Increased grazing land management intensification through the selection of productive species and the use of N affects the amount and quality of C and N inputs to the soil. This study evaluated the short-term impacts of litter quality on litter decomposition and C and N distribution among soil size-density fractions. A 168-d litter bag mesocosm experiment and a 120-d incubation study evaluated the decomposition of three perennial species [rhizoma peanut (Arachis glabrata Benth., RP), bahiagrass (Paspalum notatum Flügge; BG), and sawpalmetto (Serenoa repens Bartr., SP)] on grazing land soils with contrasting C concentrations (3.4 and 18 g C kg −1 ; Buck Island Ranch and Ona, respectively). Soil did not affect litter decomposition. There was less remaining biomass at the end of incubation for RP and BG (58%) than SP (79%). Nitrogen immobilization occurred on SP litter, probably because of its high initial lignin/N and fiberbound N/N ratios (43 and 384 g kg −1 organic matter, respectively). Litter had no effect on soil C and N concentrations in size-density fractions; however, greater proportions of C and N (∼47 and 59%, respectively) were found in the light-free fraction. Nitrogen addition promoted C and N accumulation in the mineral fraction. These results suggest plant litter chemical characteristics played a more important role on litter decomposition than soil C and N concentrations. Management intensification through changes in plant species and N fertilization had positive effects on C and N dynamics in coarse-textured soils, with enhanced decomposability of cultivated forage species relative to native vegetation.