Nutrient excretion from cattle grazing nitrogen-fertilized grass or grass-legume pastures

Authors: GARCIA, LIZA - University Of Florida; DUBEUX, JOSE - University Of Florida; SOLLENBERGER, LYNN - University Of Florida; VENDRAMINI, JOAO - University Of Florida; DILORENZO, NICOLAS - University Of Florida; SANTOS, ERICK - University Of Florida; Jaramillo, David; RUIZ-MORENO, MARTIN - University Of Florida

Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/26/2021
Publication Date: 4/14/2021
Citation: Garcia, L., Dubeux, J., Sollenberger, L., Vendramini, J., Dilorenzo, N., Santos, E., Jaramillo, D.M., Ruiz-Moreno, M. 2021. Nutrient excretion from cattle grazing nitrogen-fertilized grass or grass-legume pastures. Agronomy Journal. https://doi.org/10.1002/agj2.20675.
DOI: https://doi.org/10.1002/agj2.20675

Interpretive Summary: Nutrient cycling via livestock excreta is an important grassland ecosystem service. This study was conducted in 2016 and 2017 and determined nutrient excretion from cattle grazing three systems: 1) N-fertilized bahiagrass (Paspalum notatum Flüggé) overseeded with rye (Secale cereale L.) and oat (Avena sativa L.) during winter (Grass+N); 2) unfertilized bahiagrass overseeded with rye-oat-clovers (Trifolium sp.) mixture (Grass+clover); and 3) rhizoma peanut (Arachis glabrata Benth.) -bahiagrass mixture overseeded with a rye-oat-clovers mixture (Grass+CL+RP). Urinary volume excreted in the warm season ranged from 122 to 182 L ha-1d-1, more than double that in the cool season (56 to 70 L ha-1 d-1). Urinary N concentration during the warm season was greater in Grass+CL+RP compared with Grass+N (4.4 vs. 3.1 g kg-1 respectively). In addition, fecal DM and OM output was greater for Grass+N than for steers grazing Grass+CL+RP during the warm season (3.8 and 3.2 vs. 2.8 and 2.2 kg hd-1 d-1, respectively). Total annual feces excretion of P, K, Mg, and N were greater in the Grass+N than in Grass+CL+RP system. The introduction of legumes increased the proportion of N returning via urine. However, when summed across seasons, total N excretion (feces and urine) was greater in the Grass+N than in Grass+CL+RP (89 vs. 71 kg ha-1 yr-1), mainly due to greater stocking rate in the former. Grass-legume systems receiving 34 kg N ha-1yr-1 recycled 80% of the N recycled in the grass system receiving 224 kg N ha-1yr-1, indicating the potential of forage legumes to add N to grasslands.

Technical Abstract: Nutrient cycling via livestock excreta is an important grassland ecosystem service. This study was conducted in 2016 and 2017 and determined nutrient excretion from cattle grazing three systems: 1) N-fertilized bahiagrass (Paspalum notatum Flüggé) overseeded with rye (Secale cereale L.) and oat (Avena sativa L.) during winter (Grass+N); 2) unfertilized bahiagrass overseeded with rye-oat-clovers (Trifolium sp.) mixture (Grass+clover); and 3) rhizoma peanut (Arachis glabrata Benth.) -bahiagrass mixture overseeded with a rye-oat-clovers mixture (Grass+CL+RP). Urinary volume excreted in the warm season ranged from 122 to 182 L ha-1d-1, more than double that in the cool season (56 to 70 L ha-1 d-1). Urinary N concentration during the warm season was greater in Grass+CL+RP compared with Grass+N (4.4 vs. 3.1 g kg-1 respectively). In addition, fecal DM and OM output was greater for Grass+N than for steers grazing Grass+CL+RP during the warm season (3.8 and 3.2 vs. 2.8 and 2.2 kg hd-1 d-1, respectively). Total annual feces excretion of P, K, Mg, and N were greater in the Grass+N than in Grass+CL+RP system. The introduction of legumes increased the proportion of N returning via urine. However, when summed across seasons, total N excretion (feces and urine) was greater in the Grass+N than in Grass+CL+RP (89 vs. 71 kg ha-1 yr-1), mainly due to greater stocking rate in the former. Grass-legume systems receiving 34 kg N ha-1yr-1 recycled 80% of the N recycled in the grass system receiving 224 kg N ha-1yr-1, indicating the potential of forage legumes to add N to grasslands.