1a. Objectives (from AD-416):
1) To quantify Volatile organic compounds (VOCs) of corn and alfalfa silages (the leading types of dairy feed) throughout all ensiling/storage/feeding phases on three commercial dairy farms; 2) To use emission data measured on these commercial farms to further refine and evaluate the existing silage VOC emission model and then use the model to evaluate the farm scale environmental benefits and economic costs of mitigation strategies; 3) To incorporate the model into software designed for use as an educational tool and/or decision aid for producers and others interested in reducing silage emissions; and 4) Develop technical recommendations and publications for on-farm silage production, management, and animal feeding practices to reduce the VOC emissions from silage sources on dairies while increasing net financial gain.
1b. Approach (from AD-416):
Three dairies will be monitored to measure volatile organic compound (VOC) emissions from corn and alfalfa silage throughout the entire silage preservation and feeding cycle. Silage samples will be taken at different times to quantify changes in silage over time. The original crop feedstock and silage samples will be analyzed for alcohols, volatile fatty acids, and aldehydes, as well as moisture content, pH, total and volatile solids, and lactic acid. Additional variables measured will include particle size, content of readily fermentable carbohydrate, moisture content, bulk density, lactic acid bacterial population, temperature, oxygen content, silage pile configuration, exposed surface area and roughness. A mobile emissions lab containing measurement instruments will be placed adjacent to the silage pile, mixer wagon, or feedlane. Flux chambers and wind tunnels will be placed on the silage surfaces that will be monitored by instruments inside the mobile lab. Two open-path instruments will be placed to monitor undisturbed emissions emanating from the silage face, the mixer wagon, and the feedlane. Gas phase monitoring of the most abundant VOCs (e.g., small alcohols) will be done using a photo-acoustic instrument and a gas chromatograph. Additional VOCs will be determined using standard procedures approved by the U.S. Environmental Protection Agency (TO-15 and TO-11A). Monitoring data will be used to refine and evaluate the Dairy Silage Emissions Model under various environmental and management scenarios. The silage model will be incorporated in a whole farm simulation model where it will be used to evaluate the performance and economics of mitigation strategies for reducing silage emissions.
3. Progress Report:
An extensive literature review of work related to silage VOC production and emission was completed. Data on volatile organic compound (VOC) concentrations, volatility and reactivity in the atmosphere were summarized and used to refine and simplify our silage VOC emission model. We calibrated the model using the mass balance data presented in a previous report (Hafner, S.D., F. Montes, and C.A. Rotz. 2012. A mass transfer model for VOC emission from silage. Atmos. Environ. 54:134-140). A process-driven model was also developed for predicting VOC emissions from manure sources on farms. The revised silage and manure VOC component models were incorporated in our farm simulation model (Integrated Farm System Model) to enable whole-farm estimation of VOC emissions along with other environmental impacts and farm economics. They were also incorporated in our DairyGEM software tool. DairyGEM (Dairy Gas Emission Model) is an educational aid for estimating ammonia, hydrogen sulfide, greenhouse gas, and now VOC emissions from dairy farms. The models are now ready for further evaluation and refinement using the data being measured on farms in this project. Following this evaluation, these software tools will be used to evaluate the environmental benefits and costs of mitigation strategies.