Construction and validation of small mobile wind tunnels for studying ammonia volatilization

Ammonia volatilization is a major nitrogen (N) loss process for surface app lied manures and urea fertilizers. Ammonia volatilization is a complex phen omenon requiring specialized research equipment to gather valid scientific data, which is essential for developing management practices to minimize N losses from farms and N inputs to neighboring ecosystems. The objectives of this work were: i) to describe a revised version of the small mobile wind- tunnels originally reported by Lockyer, and ii) to assess the ability of th ese wind tunnels to quantitatively recover ammonia lost from dilute solutio ns. The design, construction, cost (about $4000 each), physical calibration , and operation of the wind tunnels are described. The tunnels consist of t wo connected parts: i) a transparent plastic canopy which covers a 1-m(2) t reatment area, and ii) a sheet-metal cylinder, which houses an adjustable s peed motor with attached fan blade and an air sampler to monitor ammonia vo latilization. Two ammonia loss-and-recovery experiments were conducted at c onstant wind speeds of 0.5 and 1.0 in s(-1) to assess tunnel performance. M ean ammonia recoveries were 104 +/-6% at 0.5 m s(-1) and 104 +/- 18% at 1.0 m s(-1). These results demonstrate that the wind tunnels can be valid tool s for collecting volatilized ammonia and for making relative comparisons am ong N management treatments. Obtaining valid comparison of different manage ment treatments is essential for the development of improved N management p ractices that minimize ammonia losses from manures or fertilizers.