See more from this Session: Forage Ecology, Physiology, and Nutritive Value
Wednesday, November 3, 2010
Long Beach Convention Center, Exhibit Hall BC, Lower Level
The objective was to evaluate N2O emissions from ungrazed (exclosed), grazed and urine spot sites within sainfoin (S) and alfalfa-grass (A+G) pastures. . Pastures were established in 2003 with grazing and N2O data collection from 2004 to 2006. The experimental design was a 2 X 2 factorial (pasture: S and A+G and pasture utilization: 50 and 70%) with three replications. Urine was collected and composited from steers on each pasture type. Then 500 mL of un-acidified urine was applied to corresponding pastures in July to simulate a urine spot. Gas samples were collected weekly using a non-flow through non steady-state method from early April until freeze-up. Annual N2O-N loss estimates were calculated for each sampling unit by linear interpolation. N2O emissions from ungrazed sites for both pastures were low. Estimated losses were 0.3 kg N2O-N ha-1 or less for 2 of 3 years on S, and for all years on A+G pastures. Although higher (P<0.01) N2O emissions were observed on the S than A+G pasture the estimated cumulative loss from the S pastures was no more than 0.7 kg N ha-1 y-1. The N content of the urine collected from the cattle varied widely among animals and pastures which resulted in inconsistent trends relating urine N content with pasture type and utilization. Combining soil-emitted and urine-emitted N2O emissions and soil CH4 consumption, resulted in “net” CO2 equivalents of between 20 and 300 kg CO2 ha-1 yr-1, with no significant differences between pasture types or utilization rate.