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 b y incorporation of the manure into the soil. The degree of reduction depend s on the method of incorporation and the time-lag between application and i ncorporation. In general, direct incorporation with a mouldboard plough yie lds more reduction than incorporation by a fixed tine cultivator. Direct in corporation is not always achievable. In practice, there will always be som e time between the spreading and incorporation and during this time volatil ization of ammonia from the surface-applied manure takes place. Previous st udies do not account for the effect of the time-lag between spreading and i ncorporation on the ammonia losses. To assess the ammonia volatilization af ter spreading and incorporation of manure, the time-lag between these two o perations was modelled via computer simulation. The model developed include s plot size, work capacity of the spreader, work organization, incorporatio n method, capacity of the incorporator, volatilization rate of surface appl ied manure, potential volatilization reduction by the incorporator and appl ication rate. The simulation results are only valid for a specific set of i nput parameters. Time-consuming simulation runs are required to draw genera l conclusions. Therefore, a generalized model was also developed to approxi mate in a simplified way the influence of capacities of the spreader and in corporator on the volatilization reduction without simulating the whole pro cess of spreading and incorporating. In a case study, the effect of the cap acity of an incorporator and spreader on the reduction of volatilization wa s calculated. The case study showed that incorporation by a mouldboard plou gh does not always result in lower ammonia volatilization than incorporatio n 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 tin e 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 manu re applied and incorporated on arable land. The model could be used as a co mprehensive instrument to evaluate the effect of different management strat egies for manure spreading and incorporation on ammonia volatilization when applying and incorporating manure on a plot scale. (C) 1999 Silsoe Researc h Institute.