Simulation of Greenhouse Gas Emissions after Land Application of Cattle Manure.

Land application of cattle manure is a cost effective source of nutrients and organic matter for crop production.  However, emissions of greenhouse gases after land application contribute to air pollution impacting public health and welfare. Knowledge of gas transport mechanisms in manure-amended soils is an important part of predicting gaseous emissions from land application practices. A predictive empirical model was developed based on detailed numerical simulations of wetting and drying processes in manure using HYDRUS-1D. Similar to the principle of soil respiration, the fundamental model parameters, considered in gas production from land application of manure, include water content, temperature, and soil/manure characteristics. Because of the temperature dependency of gas transport processes, heat transport was also included in the simulations. The model was calibrated and validated based on field measurements of gaseous emissions after surface application of four different manure sources (i.e. dairy manure, beef manure, dairy compost, and beef compost). Soil/manure moisture contents were monitored during the course of measurements using dielectric sensors. The developed model provides improved means for estimation of greenhouse gas emissions from land-applied manure, based on the physical and thermal soil and manure properties.