Pastures under dry climate can be cold spots for soil nitrous oxide emissions from grazing cattle excreta

Animal excreta is an important contributor to agricultural nitrous oxide (N2O) emissions – a potent greenhouse gas. Soil N2O emissions are episodic in nature and commonly subjected to large inter-annual and spatial variation. Thus, edaphic-climatic specific studies are needed to further our knowledge on global terrestrial N2O losses and to more accurately estimate national N2O emissions. For the Canadian Prairies, multi-year studies are needed for the determination of beef cattle dung and urine derived N2O emissions under semiarid and sub-humid climate and different soil types, a knowledge gap explored by the present study. We evaluated N2O emissions in dung, urine, and unfertilized control plots following six animal excreta applications in 2009/10 and 2010/11. The experiment was conducted in two locations: (i) Swift Current, Saskatchewan (semiarid prairies/brown Chernozem); and, ii) Lacombe, Alberta (sub-humid prairies/black Chernozem). Our results indicated that beef cattle dung-N derived N2O emission was negligible for all excreta applications on both sites as cumulative N2O emissions were not significantly different from the control plots (p > 0.05). Overall, cattle urine derived soil N2O emission was greater than emissions from dung and control plots, and subjected to large inter-annual variation. For the Swift Current site, 2010 experienced record-high precipitation that stimulated N2O emissions of up to 0.47% of the applied urine-N. Except for the applications exposed to record-high precipitation, the percentage of the urine-N lost as N2O at the Swift Current site was small, ranging from 0.00% to 0.01%. Similarly, for the Lacombe site, urine-N derived N2O emissions ranged from 0.00% to 0.12%, always lower than the 0.32% default IPCC (2019) emission factor used for cattle urine-N. Our results suggest that dry climate locations under near-normal or below-normal precipitation levels are natural "cold spots" for N2O emissions and could experience negligible cattle excreta derived soil N2O emissions.