Legume Proportion in Mixed-Species Swards Affects Litter Decomposition and Nutrient Release Rates.

Mixed grass-legume swards are one of the best alternatives to increase sustainability of grazing systems and reduce dependence on external inputs, particularly N fertilizer. We hypothesize that increasing proportion of legume in forage mixtures or adding N fertilizer to grass monoculture will impact nutrient cycling in pastures by affecting litter decomposition and nutrient release rates. The objective of this study was to quantify litter decomposition and nutrient disappearance of bahiagrass (BG; Paspalum notatum Flügge)-based pastures as affected by N fertilizer or proportions of ‘Florigraze’ rhizoma peanut (RP; Arachis glabrata Benth.). Five treatments (litter source) were replicated six times in a randomized complete block design. Litter treatments were derived from 100% grass either as unfertilized BG or BG fertilized with 60 kg N ha^-1, 67% BG-33% RP, 33% BG-67% RP, and 100% RP. For RP, litter was defined as leaflets from soil level to a 15-cm height collected from a 20-cm tall RP sward canopy. The top 5-cm canopy layer was discarded to eliminate the youngest leaflets. Bahiagrass litter was considered to be leaf blade from the entire sward canopy to soil level. Bags for incubation were 15 x 20 cm, made of 100% polyester fabric, and were filled with 12 g of litter before heat sealing. Treatments were incubated in the field for 4, 8, 16, 32, 64, and 128 d. Litter relative decomposition rate and chemical composition, including C:N, C:P, and lignin concentration were evaluated using various mathematical models. Mass (% of initial), C:N, and C:P of litter remaining at Day 128 were greater  (p<0.01) for unfertilized BG than the other treatments, but there were no differences among the other treatments in these responses. Legume proportion did not affect litter decomposition compared with N-fertilized bahiagrass, but litter from all legume and N-fertilized treatments decomposed faster than unfertilized grass.