AMMONIA VOLATILIZATION FOLLOWING APPLICATION OF LIVESTOCK MANURE TO ARABLE LAND

Ammonia volatilization from land-spreading of livestock manure was investigated by using a new micrometeorological measuring method based on passive diffusion sampling close to the ground surface. The approach implies that estimates of two parameters must be made: (1) the driving force, that is, the difference between the equilibrium concentration (C(eq)) and the ambient concentration (C(a,z)), and (2) the surface resistance represented by a mass transfer coefficient (K(z,a)). The effect of factors related to meteorology, soil/manure characteristics and mode of application on NH3 volatilization was examined in the laboratory and some of the results were validated by field experiments. Temperature influenced C(eq) according to a mathematical relationship, although absolute concentration level could not be estimated on the basis of temperature, pH and ammonia content only. It was suggested that temperature and air humidity interact in the dynamics of the ammonia volatilization process, primarily by establishing changes with time by an ammonia enrichment factor. Manure fluidity, a parameter related to dry matter content, substantially influenced C(eq), as did the mode of application. By means of incorporation, volatilization rates could be reduced by as much as 83 to 98%, depending on type of manure and mode of incorporation. Differences in application rates did not influence the relative C(eq) but a linear relationship was suggested between the fraction of surface area covered and the initial C(eq). Volatilization from band spreading and broadcast spreading followed different time courses in the initial stage after application but the cumulative loss difference was similar with time.