Ammonia volatilization during storage of cattle and pig slurry: effect of surface cover

Abstract

SUMMARY: 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® (pebbles of burned montmorillonitic clay) and a lid were tested as additional covers. Convective transport of ammonium to the surface layers caused NH₃ volatilization losses of 3–5 g NH₃-N/m² per day from the stirred, uncovered tanks. The loss of NH₃ from the stirred slurry was related to air temperature. The development of a natural surface crust reduced NH₃ losses to 20% of those from stirred slurry. NH₃ losses from slurry not developing a natural surface crust layer and left undisturbed were similar to the losses from stirred slurry. A 15 cm layer of straw was as effective as a surface crust layer in reducing NH₃ losses. In one experiment, cracks developed in the oil cover and losses were therefore only reduced to 50% of those of uncovered slurry. Apart from this experiment, NH₃ losses from slurry covered with oil, leca®, peat and foil were small.