The Impact of the Oasis Effect on Wind Tunnel Measurements of Ammonia Volatilization from Urea-Fertilized Agricultural Land

Devon Watt1, Philippe Rochette2, Ian B Strachan1, Normand Bertrand2 and Andrew VanderZaag3, (1)McGill University, Department of Natural Resource Sciences, Montreal, QC, Canada, (2)Agriculture and Agri-Food Canada (AAFC), Quebec, QC, Canada, (3)Agriculture and Agri-Food Canada, Science and Technology Branch, Ottawa, ON, Canada

Contact First Author: Devon Watt; devon.watt@mail.mcgill.ca

Abstract ID#: 35905

 

English Abstract:
The average losses of nitrogen (N) in the form of ammonia (NH3) from agricultural land treated with synthetic fertilizers are 10-19% of applied N, and urea is the most widely used synthetic fertilizer globally.1 The lack of efficiency of urea as a fertilizer is an economic issue for producers, and the ammonia being emitted to the atmosphere can negatively impact human and ecosystem health.1 The oasis effect can be defined as the decrease in NH3 volatilization rate downwind from the leading edge of the fertilized plot, and is caused by the reduction of the concentration gradient of NH3 near the emitting surface. It is a potential bias that could result in erroneously high emission factors calculated from wind tunnel NH3-flux measurements.2 Two 24 m long wind tunnels were constructed indoors over soil plots fertilized with surface-applied urea, and measurements of NH3 concentration taken every 2 m along the tunnel were used to test for the oasis effect. Out of the 85 periods of data collected, 58 resulted in the distance from the entrance of the tunnel having a significant linear effect on NH­3­ concentration above the plot (α=0.05), indicating the absence of the oasis effect for those periods. In addition, 37 out of the 38 periods with linear regression coefficients greater than 10-5 show that distance from the entrance of the tunnel is a significant regression parameter for NH3 concentration along the tunnel. Therefore during the periods when the largest losses of NH3 occurred, the concentration profiles along the tunnel were not significantly affected by the oasis effect.

 1Bouwman, A.F., et al. 2002. Estimation of global NH3volatilization loss from synthetic fertilizers and animal manure applied to arable lands and grasslands. Global biogeochem. Cycles. 16: 1024.

 2Sintermann, J., et al. 2012. Are ammonia emissions from field-applied slurry substantially over-estimated in European emission inventories? Biogeosciences. 9(5): 1611-1632.

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