A simple mathematical method to estimate ammonia emission from in-house windrowing of poultry litter

In-house windrowing between flocks is an emerging sanitary management practice to partially disinfect the built-up litter in broiler houses. However, this practice may also increase ammonia (NH₃) emission from the litter due to the increase in litter temperature. The objectives of this study were to develop mathematical models to estimate NH₃ emission rates from broiler houses practicing in-house windrowing between flocks. Equations to estimate mass-transfer areas form different shapes windrowed litter (triangular, rectangular, and semi-cylindrical prisms) were developed. Using these equations, the heights of windrows yielding the smallest mass-transfer area were estimated. Smaller mass-transfer area is preferred as it reduces both emission rates and heat loss. The heights yielding the minimum mass-transfer area were 0.8 and 0.5 m for triangular and rectangular windrows, respectively. Only one height (0.6 m) was theoretically possible for semi-cylindrical windrows because the base and the height were not independent. Mass-transfer areas were integrated with published process-based mathematical models to estimate the total house NH₃ emission rates during in-house windrowing of poultry litter. The NH₃ emission rate change calculated from the integrated model compared well with the observed values except for the very high NH₃ initial emission rate from mechanically disturbing the litter to form the windrows. This approach can be used to conveniently estimate broiler house NH₃ emission rates during in-house windrowing between flocks by simply measuring litter temperatures.