Reducing N Inputs in Grazing Systems By Introducing Rhizoma Peanut.

Nitrogen fertilizer increases carbon footprint of livestock systems. Forage legumes are a possible alternative to replace N fertilizers. Rhizoma peanut - RP (Arachis glabrata Benth.) is one of the few warm-season perennial legumes that have demonstrated persistence under a range of grazing conditions. This research evaluated the potential benefits of including RP in livestock-forage systems in North Florida. The experiment was conducted from July to October of 2015 and will be repeated in 2016. Treatments consisted of three livestock production systems as follows: 1) Argentine bahiagrass fertilized with 113 kg of N ha^-1 (BHF); 2) unfertilized Argentine bahiagrass (BH); 3) Strip-planted Ecoturf rhizoma peanut mixed with Argentine bahiagrass (BHR). Treatments were replicated in three blocks in a randomized complete block design. Pastures were continuously grazed using a variable stocking rate.  No treatment × evaluation period (P = 0.52), or treatment effect (P = 0.06) were found for herbage allowance. Treatment x evaluation period effects were observed for ADG (P = 0.05) and herbage mass (P = 0.02). Stocking rate and gain per area did not differ among treatments (P > 0.05). Season ADG was 0.33, 0.22, and 0.16 kg head^-1 d^-1 for BHR, BHF, and BH, respectively. Fecal δ¹³C indicated that an average of 72% of C found in the feces of cattle grazing RP paddocks were from C₃ species. Fecal N concentration was greater from samples collected from cattle grazing RP (22.8 g N kg^-1) than cattle grazing BH (17.7 g N kg^-1). Greater proportion of C₃ species in the diet of cattle grazing RP was also reflected in plasma and red blood cells using δ¹³C. Including RP strip-planted into bahiagrass pastures allowed reduction of N fertilization and maintained livestock gain per area when compared to systems without legumes, whether fertilized or not with nitrogen.

Keywords: Rhizoma peanut, N fertilizer, beef cattle.