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United States Department of Agriculture

Agricultural Research Service

Research Project: Modeling Silage Emissions for Improved Air Quality

Location: Pasture Systems & Watershed Management Research

2013 Annual Report


1a.Objectives (from AD-416):
1. To quantify volatile organic compounds (VOCs) of corn and alfalfa silages 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 decision aid for producers and others interested in reducing silage emissions. 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 assessed for VOC emissions from corn and alfalfa silage throughout the entire silage/feeding life cycle. Solid/liquid silage samples will be taken at different time points so that the changes in silage over time can be quantified. These data will be used to refine and evaluate a model for predicting silage VOC emissions. Measured emissions of single VOC compounds will be compared to those predicted by the model for each of the important compound groups used in the model, i.e. alcohols, alkenes, and aldehydes. Model parameters such as mass transfer coefficients will be modified as needed to assure accurate emission predictions of these compounds. The model will be further evaluated by comparing predictions to measurements from independent datasets.

As confidence in the silage model is established, this component will be incorporated in the Integrated Farm System Model. This whole farm model will be used in the simulation of farming systems to determine baseline, whole farm emission data. Mitigation techniques such as alternative silage facilities, feeding frequency, covers, and wind breaks will be evaluated to determine their potential to reduce farm level emissions and the ozone forming potential of those emissions.

The silage emission model will also be incorporated in an educational software tool called the Dairy Gas Emission Model or DairyGEM. This will provide a simpler tool with more graphical output for broader use in education and training of producers and others interested in silage production and feeding.


3.Progress Report:

This short term project was completed in March. The services of Hafner consulting were employed to complete ongoing work in measuring and modeling volatile organic compound (VOC) emissions from silage.

Cooperator spent time in California working with staff of the University of California in Davis designing and conducting experiments to measure silage emissions. An extensive literature review of work related to silage VOC production and emission was also completed. Data on VOC concentrations, volatility and reactivity in the atmosphere were summarized and used to refine and simplify our silage VOC emission model.

The revised silage VOC component was incorporated in our farm simulation model (Integrated Farm System Model) to enable farm scale estimation of silage VOC emissions along with other environmental impacts and farm economics. The silage VOC component was 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. Both software tools are now fully functioning and verified to predict reasonable VOC emissions as influenced by silage storage and management procedures. Further evaluation with measured farm data is underway to test the accuracy in predicting farm emissions.


Last Modified: 11/22/2014
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