Validating the MAVIS model for optimizing incorporation of litter-based manures to reduce ammonia emissions
The Manure Ammonia Volatilization and Incorporation System (MAVIS) identifies the optimum method of incorporating solid (litter-based) manures (FYM) to reduce ammonia (NH3) emission following spreading. The model allows the user to specify the geometry of the field to be manured and the parameters of the spreader and incorporator machinery and calculates NH3 volatilization for the defined area. Incorporation machinery work rates depend on the available tractor engine power and the power demand of the cultivation implement. Validation of the output showed an acceptable agreement with survey data of achieved work rates over a range of tractor power availabilities. The work rates achieved by plow types are approximately 40% to 50% of the greatest work rate achievable with disk incorporators for primary cultivation (20 to 25 cm depth). Incorporation by the slow, but efficient, plow always reduced NH3 emissions by more than the faster, but less efficient, disk or tine implements. Typically, incorporation by plowing could limit NH3 emissions to approximately 16% of total ammoniacal-N (TAN); the smallest emissions from incorporation by disk harrow or straw incorporation were approximately 30% and 38% of TAN applied, respectively. These differences were almost unaffected by differences in field size, applicator volume, or manure application rate. It should be noted that, when applied to the field scale, there is still an appreciable loss of NH3 even with the optimum application method, despite reductions in plot experiments of up to 98% of NH3 emissions. The allocation of labor between spreading and incorporation had little effect on model outcome for small fields but led to NH3 emissions ranging from 40% of TAN on fields >10 ha.