1a. Objectives (from AD-416)
To minimize downstream nutrient loss in a Chesapeake Bay subwatershed by identifying and encouraging strategic, cost-effective combinations of farm management practices and technologies.
1b. Approach (from AD-416)
Whole-farm and watershed-level models, such as the Integrated Farm System Model (IFSM) and the Soil and Water Assessment Tool (SWAT) will be used to simulate current farm and watershed conditions in the Conewago Watershed in PA. This watershed drains to the Chesapeake Bay and is becoming a focus watershed for a range of research groups on how to more effectively and efficiently control nonpoint source pollution within the Bay catchment. The economic and environmental impact of various agriculturally-based, nonpoint source control combinations will be simulated using the above models in conjunction with literature findings and simple mathematical models. Evaluation of results will include consideration of the predictive and estimated uncertainty of major variables within the natural system. These evaluations will provide comparative efficiencies of various management combinations on protecting and improving water quality within the Chesapeake Bay. Results will be transferred to stakeholders through connections with Penn State Extension.
3. Progress Report
Experimental trials were conducted to measure the Henry’s constant, disassociation coefficient, and emission rate of ammonia from ammonium solution and manure sources. Measured parameters for ammonium solutions were found to agree relatively well to values predicted by theoretically derived models of the ammonia emission process. However, for manure the disassociation of ammonia was found to be considerably greater than that predicted. This difference was found to be caused by increased pH on the manure surface created by the formation and release of carbon dioxide. This led to further trials to isolate and quantify this pH effect. Refined theoretical expressions were developed to predict emission as a function of the temperature, surface pH, and ionic strength of dairy manure and the velocity of air flowing over the manure. Experimental results compared well to values predicted using these theoretical expressions derived from ammonia volatilization literature. An extensive literature review was conducted to document past work in measuring and modeling hydrogen sulfide emissions from all types of livestock operations. Potential sources identified for dairy operations were the animal, manure on the barn floor, manure in storage, and manure following field application. The most important source was found to be manure storages. A previously developed process-level model of swine manure storage was adapted to dairy manure. Experimental trials were conducted to measure the hydrogen sulfide emissions from a manure surface. The emission rate was found to peak 8 to 12 hours after deposition and then decline with little emission after 24 hours. Measured emission rates were similar to those reported in the literature. The process level models developed for ammonia and hydrogen sulfide were integrated into our whole farm simulation model for predicting farm scale emissions and the interactions among emission sources. The model was verified to function properly and to predict reasonable emission levels for the barn floor, manure storage, and field applied manure. The farm model is being used to estimate farm level ammonia and hydrogen sulfide emissions and the impact of management on these emissions. Software tools using these models have been released for general use in estimating farm emissions and evaluating mitigation techniques for reducing emissions. Progress is monitored via email and conference calls.