EFFECT OF SPREADING METHOD, APPLICATION RATE AND DILUTION ON AMMONIA VOLATILIZATION FROM CATTLE SLURRY

Results from a series of five small-scale plot experiments which simulated different strategies for lowering ammonia volatilization following slurry application to grassland are reported. Strategies studied were band spreading, shallow-channel application, spike injection, rate of surface application and dilution. Volatilization was measured over the first 4 h following application with ventilated enclosures. Band spread slurry resulted in 0.4 of the volatilization that occurred from surface application of the same rate of slurry. The benefit of band spreading was shown to arise from higher application rates in the bands when compared with the same quantity of slurry spread over the surface. When surface-spread slurry was applied to the same depth of slurry as in bands, the volatilization per unit volume of slurry was the same. Shallow-channel application was more effective than band spreading and lowered volatilization per unit volume of slurry to <0.1 of that from surface-spread slurry. Spike injection was equally effective as shallow-channel application but, owing to perceived difficulties in machine design, construction and operation, was deemed impractical. Shallow-channel application has potential, though further work is required to optimize centre-to-centre spacing of the channels. As the application rate of surface-applied raw slurry increased, ammonia volatilization per unit volume of slurry applied decreased. Application at 50 m3 ha-1 resulted in 0.4 of the specific volatilization per unit volume of slurry that occurred at 6.3 m3 ha-1. Within the dilution treatments, the amount of water added to the slurry was linearly and inversely related to volatilization. At a dilution of 0.9-1.2:1 water: slurry the specific volatilization per unit volume of slurry was 0.5 of that from undiluted slurry.