Nitrous Oxide Emission From Sainfoin and Alfalfa+Grass Pastures.

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.