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Impact of the oasis effect on wind tunnel measurements of ammonia volatilization from urea

Watt, Devon, Rochette, Philippe, VanderZaag, Andrew, Strachan, Ian B., Bertrand, Normand
Canadian journal of soil science 2016 v.96 no.4 pp. 485-495
air, ammonia, emissions, emissions factor, oases, soil, urea, volatilization, wind tunnels
The validity of emission factors derived from small-scale measurements of ammonia (NH₃) volatilization has been questioned in the literature because gaseous NH₃ concentration gradients differ at the edge of the measurement plot and may result in higher emissions than at field scale. We studied this “oasis effect” using two very long (22 m) wind tunnels constructed indoors over soil plots fertilized with surface-applied urea (20 g N m⁻²). We hypothesized that NH₃ flux would be highest at the start of the tunnel and decrease with distance. Air NH₃ concentration was measured every 2 m along each tunnel for 2 wk after urea application; NH₃ flux did not decrease along the length of the tunnels. Of the 60 measurement periods, when there was significant NH₃ volatilization, only two had a significant nonlinear relationship (P ≤ 0.05) between NH₃ concentration and distance. For the other periods, the NH₃ concentration increased linearly with distance (P ≤ 0.05). The background NH₃ concentration difference between halves of the tunnels was not significantly related to NH₃ flux difference (P > 0.1). Our results indicate that wind tunnel measurements of NH₃ volatilization fertilized using urea are not impacted by a measurable oasis effect.