A Model for Ammonia Volatilization after Surface Application and Subsequent Incorporation of Manure on Arable Land

When applying manure to arable land by surface spreading, volatilization of ammonia takes place. Reduction of ammonia volatilization can be achieved by incorporation of the manure into the soil. The degree of reduction depends on the method of incorporation and the time-lag between application and incorporation. In general, direct incorporation with a mouldboard plough yields more reduction than incorporation by a fixed tine cultivator. Direct incorporation is not always achievable. In practice, there will always be some time between the spreading and incorporation and during this time volatilization of ammonia from the surface-applied manure takes place. Previous studies do not account for the effect of the time-lag between spreading and incorporation on the ammonia losses. To assess the ammonia volatilization after spreading and incorporation of manure, the time-lag between these two operations was modelled via computer simulation. The model developed includes plot size, work capacity of the spreader, work organization, incorporation method, capacity of the incorporator, volatilization rate of surface applied manure, potential volatilization reduction by the incorporator and application rate. The simulation results are only valid for a specific set of input parameters. Time-consuming simulation runs are required to draw general conclusions. Therefore, a generalized model was also developed to approximate in a simplified way the influence of capacities of the spreader and incorporator on the volatilization reduction without simulating the whole process of spreading and incorporating. In a case study, the effect of the capacity of an incorporator and spreader on the reduction of volatilization was calculated. The case study showed that incorporation by a mouldboard plough does not always result in lower ammonia volatilization than incorporation by a fixed tine cultivator. The lower capacity of the plough results in a larger overall time-lag between spreading and incorporation and therefore the eventual volatilization reduction is lower than that with the fixed tine cultivator, despite the higher potential volatilization reduction of the mouldboard plough. The model showed that the time-lag between spreading and incorporation should be considered when assessing ammonia losses from manure applied and incorporated on arable land. The model could be used as a comprehensive instrument to evaluate the effect of different management strategies for manure spreading and incorporation on ammonia volatilization when applying and incorporating manure on a plot scale.