PSII-17 Impact of forage diversity on animal production, forage productivity and nutritive value, emissions, and soil C/N cycling

Abstract The study objective was to compare animal performance, enteric methane production, forage productivity, and soil GHG flux of two grazing systems: 1) A botanically diverse, mixed-species pasture (COMP), and 2) A simple alfalfa:orchardgrass system (SIMP). Fifty-six steers (BW = 318.29 ± 37.58 kg) were adapted to a GreenFeed Emission Measurement System (GEM; C-Lock Inc., Rapid City, SD) and stratified into treatments based on acclimation. Each treatment consisted of 4 paddocks, three 3.2 ha and one 1.6 ha paddock, with 8 steers and 4 steers each, respectively. Animals grazed for 104 d from June to October 2018, and shrunk BW was recorded at the onset of grazing and every 50 d thereafter to determine ADG. Soil CO2, CH4, and N2O flux was measured at the beginning and end of the grazing season using 10 static chambers in 3 paddocks/trt for 5 d post-grazing. Forage production was measured bi-weekly in pre- and post-grazed sub-paddocks, and forage quality was analyzed using near-infrared reflectance spectroscopy. Crude Protein content was lower in COMP than SIMP pastures (15.93% vs. 18.28%; P < 0.0001) and NDF content (41.51% vs. 43.63%, for COMP and SIMP; P = 0.0032). Enteric methane production was significantly lower for COMP steers (167.7 g/d vs. 209.38 g/d for COMP and SIMP; P < 0.0001) and emission intensity (g CH4/kg LWG; 158.65 vs. 200.6 for COMP and SIMP; P < 0.0001). Methane yield did not differ between COMP and SIMP treatments (5.37 vs. 5.03%, respectively; P > 0.05), but were 17 and 23% lower than current IPCC tier II recommended Ym values (6.5 ± 1.0%). Animal performance and soil GHG flux did not differ between treatments (P > 0.05). These results indicate that, while both treatments perform well in comparison to IPCC estimates, the COMP trt may result in a lower carbon footprint.