Manure-DNDC: Building a Process Based Biogeochemical Tool for Quantifying Ammonia
and GHG Emissions and Mitigation Opportunities for California Dairies

William Salas
Applied Geosolutions, LLC, 87 Packers Falls Road, Durham, NH

Changsheng Li
Institute for the Study of Earth, Oceans and Space, University of New Hampshire, Durham, NH

Assessing the environmental impact of manure management is difficult due to high variability in the quality and quantity of animal waste, and in the numerous factors affecting the biogeochemical transformations of manure during storage, treatment and field application. There is an urgent need for scientifically sound, mass balance based, process models for quantifying air emissions from animal feeding operations. Measurement programs are essential, but must be supplemented by process-oriented modeling that incorporates mass balance constraints to extrapolate in both space and time (NRC, 2003). The time is right for moving beyond the inadequate emission factor approach by developing process based models for quantifying air emissions from animal feeding operations.

The dynamics of CH4, N2O and NH3 production/consumption is always controlled by several biochemical and geochemical reactions, namely decomposition, hydrolysis, nitrification, denitrification, ammonium adsorption, chemical equilibriums of ammonium/ammonia, and gas diffusion. These biogeochemical processes are currently simulated in our existing model called DeNitricifation-DeComposition, or DNDC. DNDC simulates these processes under both aerobic and anaerobic conditions, thus is well suited for estimating C and N dynamics and air emissions associated with manure production, storage, treatment and land application.

The current DNDC model has detailed processes for quantifying CH4, N2O and NH3 emissions from agroecosystems with fertilizer/manure application or animal grazing conditions but lacks algorithms for specifying fluxes under drylot, housing and storage conditions. We are now extending DNDC’s applications by integrating the fundamental biogeochemical processes with housing and storage management practices. The new developments for our process-based, mass balance approach include (1) integration of detailed biogeochemical processes into the GHG emissions and NH3 volatilization under drylot, housing or storage conditions; (2) characterization of environmental factors under drylot, housing or storage conditions; and (3) characterization of quantity and quality of dairy waste. This paper provides an overview of our on-going project supported by USDA and California Energy Commission to develop Manure-DNDC modeling system including GIS databases for California dairies, perform a field measurement program and perform model refinements to create a tool for quantifying air emissions from California dairies.