Nutrient Cycling through Livestock Excreta in N-Fertilized or Grass-Legume Pastures.

The objective was to assess nutrient cycling by measuring total fecal output in cattle grazing three forage systems. The experiment was conducted from January to October 2016 in a grazing trial at the University of Florida, North Florida Research and Education Center. Treatments consisted of three forage systems as follows: 1) N-fertilized bahiagrass (Paspalum notatum Flügge) pastures (113 kg N ha^-1) during the warm season, overseeded with a mixture (45 kg ha^-1 of each) of ‘FL 401’ cereal rye (Secale cereale L.) and ‘RAM’ oat (Avena sativa L.) during the cool season (BHF); 2) rhizoma peanut (Arachis glabrata Benth.)-bahiagrass pastures during the warm season, overseeded with the rye-oat mixture fertilized with 34 kg N ha^-1 plus a mixture of clovers (Trifolium sp.) during the cool season (BHR); and 3) unfertilized bahiagrass pastures during the warm season, overseeded with the rye-oat-clover mixture + 34 kg N ha^-1 during the cool season (BH). Dry matter intake (DMI) was determined by measuring total fecal output with the marker dilution technique (Cr₂O₃ and TiO₂ as markers) and in vitro digestibility from composited hand-plucked samples from each pasture during the days of marker dosing. Cattle DMI, either as kg hd^-1 d^-1 or as percentage of body weight, did not differ (P > 0.10) among treatments in either the cool or the warm season. Fecal OM output was similar across treatments in the cool season (P = 0.14). In the warm season, BHR steers had decreased (P < 0.05) fecal OM output when compared to BHF (1.80 vs. 2.8 kg hd^-1 d^-1). Excretion of P, K, Ca, and Mg was similar across treatments in both seasons (P > 0.10). In conclusion, similar intake and decreased fecal output in BHR may indicate a greater digestibility of legume-containing pastures in the warm season when rhizoma peanut is present.