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A Passive Flux Sampler for Measuring Ammonia Volatilization from Manure Storage Facilities

Dep. of Soil Science, Danish Inst. of Plant and Soil Science, Research Centre Foulum, P.O. Box 23, DK-8830 Tjele, Denmark;
The Danish Agricultural Advisory Centre, Udkærsvej 15, DK-2800 Å rhus, Denmark;
Dep. of Agricultural Sciences, Section of Soil, Water, and Plant Nutrition, The Royal Veterinary and Agricultural Univ., Thorvaldsensvej 40, DK-1871 Frederiksberg C, Copenhagen, Denmark.

^* Corresponding author (sgs%pvf%plante2{at}foulum.min.dk).

ABSTRACT

An integrated horizontal flux technique was tested for quantification of ammonia (NH₃) emission from manure storage. The method is based on a simple and inexpensive passive flux sampler consisting of two disconnectable glass tubes, coated on the inside with oxalic acid. The flux sampler is mounted at a minimum of three heights, 20 to 100 cm above the storage, on each of four masts, placed perpendicular to each other around the storage. The samplers continuously integrate the horizontal flux of NH₃ at the various heights. After analysis of the NH₃ content in the tubes facing the storage (exposed tubes) and surroundings (background tubes), the vertical flux of NH₃ from the storage can be obtained by application of mass balance equations (micrometeorological mass balance technique). For the measurements of NH₃ volatilization from slurry tanks or lagoons the technique is useful, because it is not affected by heterogenity in wind profiles and the masts with the passive flux samplers are placed on the periphery of the slurry store. The flux samplers were able to accurately quantify NH₃ volatilization from slurry tanks. From above the rim of the slurry tank the horizontal net flux decline exponential with height. This may facilitate the calculation of the vertical flux of NH₃. Bypass of NH₃ between exposed and background tubes may occur during periods with high wind velocities (>10 m s^–1) or when more than one-fifth of the oxalate in the exposed tube has reacted. However, if bypass occurs, a good estimate of NH₃ volatilization can still be obtained by addition of exposed and background tubes, because the NH₃ flux from storage are usually much greater than the flux from surroundings. Bypass due to high net horizontal fluxes of NH₃ can be avoided by reducing the measuring period or increasing the length of the tubes. Storm conditions with heavy rain can flood the flux samplers and spoil the measurements. Within the study NH₃ volatilization from stored cattle slurry were measured eight times from October to December 1992. Daily loss rates of NH₃ varied between 0.33 and 4.15 g NH₃-N m^–2 d^–1.