AMMONIA VOLATILIZATION DURING STORAGE OF CATTLE AND PIG SLURRY - EFFECT OF SURFACE COVER

Gaseous NH3 losses from pig and cattle slurry stored in eight storage tanks were measured simultaneously using wind-tunnels. The slurry was either stirred weekly (uncovered), or-was allowed to develop a natural surface crust. Oil, peat, chopped cereal straw, PVC foil, leca(R) (pe bbles of burned montmorillonitic clay) and a lid were tested as additi onal covers. Convective transport of ammonium to the surface layers ca used NH3 volatilization losses of 3-5 g NH3-N/m2 per day from the stir red, uncovered tanks. The loss of NH3 from the stirred slurry was rela ted to air temperature. The development of a natural surface crust red uced NH3 losses to 20 % of those from stirred slurry. NH3 losses from slurry not developing a natural surface crust layer and left undisturb ed were similar to the losses from stirred slurry. A 15 cm layer of st raw was as effective as a surface crust layer in reducing NH3 losses. In one experiment, cracks developed in the oil cover and losses were t herefore only reduced to 50 % of those of uncovered slurry. Apart from this experiment, NH3 losses from slurry covered with oil, leca(R), pe at and foil were small.