Ammonia emissions from pig and cattle slurry in the field and utilization of slurry nitrogen in crop production Doctoral Dissertation

Volatilization of ammonia (NH3) from animal manure is a major pathway for nitrogen (N) losses that cause eutrophication, acidification, and other environmental hazards. In this study, the effect of alternative techniques of manure treatment (aeration, separation, addition of peat) and application (broadcast spreading, band spreading, injection, incorporation by harrowing) on NH3 emissions in the field and on N uptake by ley or cereals was studied. The effect of a mixture of slurry and peat on soil properties was also investigated. The aim of this study was to find ways to improve the utilization of manure N and reduce its release to the environment. Injection into the soil or incorporation by harrowing clearly reduced NH3 volatilization from slurry more than did the surface application onto a smaller area by band spreading or reduction of the dry matter of slurry by aeration or separation. Surface application showed low NH3 volatilization, when pig slurry was applied to tilled bare clay soil or to spring wheat stands in early growth stages. Apparently, the properties of both slurry and soil enabled the rapid infiltration and absorption of slurry and its ammoniacal N by the soil. On ley, however, surface-applied cattle slurry lost about half of its ammoniacal N. The volatilization of NH3 from surface-applied peat manure was slow, but proceeded over a long period of time. After rain or irrigation, the peat manure layer on the soil surface retarded evaporation. Incorporation was less important for the fertilizer effect of peat manure than for pig slurry, but both manures were more effective when incorporated. Peat manure applications increase soil organic matter content and aggregate stability. Stubble mulch tillage hastens the effect in surface soil compared with ploughing. The apparent recovery of ammoniacal manure N in crop yield was higher with injection and incorporation than with surface applications. This was the case for leys as well as for spring cereals, even though NH3 losses from manures applied to cereals were relatively low with surface applications as well. The ammoniacal N of surface-applied slurry was obviously adsorbed by the very surface soil and remained mostly unavailable to plant roots in the dry soil. Supplementing manures with inorganic fertilizer N, which adds plant-available N to the soil at the start of growth, increased the overall recovery of applied N in crop yields.