Development and verification of a model simulating ammonia volatilization from soil and manure

The VOLAT model was developed to simulate ammonia volatilization in manure and soil and to be integrated as a submodel into a larger model called Manu rial Nitrogen Management: Environmental Aspects (MANIMEA). The MANIMEA mode l simulated the transformation and transportation processes affecting N in manure-amended soils, A major feature of MANIMEA is that the manure and soi l can be considered as separate components. This is important because manur e is usually left on the soil surface for a period following application an d prior to its incorporation into the soil; a significant amount of ammonia is lost by volatilization during this period. The VOLAT model was based on a nonpoint source and used a first-order governing equation. An overall ra te constant was used to take into account the effects of temperature, soil cation exchange capacity (CEC), and the air flow rate on volatilization. Th e VOLAT model was verified by comparing it to an analytical solution and by using experimental conditions and data given in the literature. Comparison of results demonstrated similar trends with some differences that ran be a ttributed to the ability of VOLAT to account for variations in temperature, CEC, and air now rates. Simulations were done for two manure application m ethods: surface application and injection. Results demonstrated that VOLAT rendered a simulation of N loss through volatilization that fell within acc eptable limits.