Quantifying Nitrous Oxide Emissions Resulting From Beef Cattle Urine and Dung on Semi-Arid Pasture.

Transformations of mineral nitrogen during manure storage and in agricultural soils account for approximately 50% of global anthropogenic emissions of N₂O. Estimates of soil N₂O emissions are made using emission factors expressed as the fraction of the N inputs that are lost as N₂O. No studies quantifying N₂O emissions induced by the deposition of urine and dung by animals grazing on pasture soils on the Canadian prairies are reported in the literature, thus the appropriateness of the current emissions factors is largely unknown. The objectives of this study were: 1) to quantify cumulative N₂O loss induced by deposition of urine and dung from beef cattle grazing on pasture and, 2) determine if the magnitudes of those losses are seasonally dependant. The study site was located in the semiarid prairie region of Saskatchewan. Mean long-term (1971-2000) precipitation is 353 mm and the mean annual temperature is 3.9 ºC.  Three treatments, urine, dung or control (no dung or urine applied) were arranged in a randomized complete-block design. Dung and urine was collected and applied to plots by hand to supply a target nitrogen loading rate of 750 kg N ha^-1 for urine and 500 kg N ha^-1 for dung. Nitrous oxide emissions from dung and urine applied at the beginning (June), middle (July) and end (October) of the grazing season were measured utilizing non-flow-through non-steady-state field-chambers. Results from the first year of the two year study (October 2009 - September 2010) are reported. Nitrous oxide emissions from the control (unamended soil) were very low, with cumulative losses estimated at 100 grams N₂O-N ha^-1. Application of dung did not significantly increase N₂O emissions compared to the control. Urine application stimulated N₂O emissions and the magnitude and duration of the increased emissions was affected by the timing of the application.  Emissions from urine applied in October or August were only marginally higher than from the control, while urine applied in June increased emissions substantially. Percent loss of the N applied as N₂O during the sampling period was estimated at 0.01% or less for urine applied in October and August, while loss estimates were 0.7% for urine applied in June.