MASS-TRANSFER COEFFICIENT AND EQUILIBRIUM CONCENTRATION AS KEY FACTORS IN A NEW APPROACH TO ESTIMATE AMMONIA EMISSION FROM LIVESTOCK MANURE

A new micrometeorological method is presented of estimating ammonia emission from soil following manure spreading by means of the stirred dynamic chamber technique in combination with passive diffusion sampling. Ammonia volatilization can be parameterized in the expression (Ceq - Ca)Kz, a where P;Ceq = ammonia equilibrium concentration in the air;. Ca = ambient ammonia concentration;. Kz, a = mass transfer coefficient between the air and the soil. Ceq is obtained from ammonia concentration measurements in the chamber. Ca and Kz, a can be measured directly in the field by using a new simple technique described in the paper. All three terms are determined by applying the passive diffusion sampler technique. A simple battery-operated chamber for field use was developed and the measuring system was tested in field experiments. The results were positive as regards replicability, simplicity in use and cost effectiveness. The relative standard deviation for duplicate determinations of concentration in the chamber was approximately 4% and the corresponding figure for the average equilibrium concentration obtained in different chambers placed in the same field was approximately 18%. This uncertainty is owing to the fact that the surface areas on which the chambers are placed are not representative of the whole areas. © 1993 Silsoe Research Institute.