2010 Annual Report
1a.Objectives (from AD-416)
To develop mathematical relationships that describe the major processes involved in the formation, release, and convective transfer of gaseous compounds from silage, and to calibrate those relationships to accurately predict emissions from feeds in silos and feed bunks.
1b.Approach (from AD-416)
Mathematical relationships will be derived that describe the biological, chemical, and physical processes involved in the formation, release, and transfer of the major gaseous compounds found in silage feeds on dairy farms. These relationships will be derived based upon theoretical or scientific understanding of the processes where rates are controlled by the characteristics of the feed and the surrounding environment. Parameters for these relationships will be determined using experimental emissions data collected in collaboration with researchers at the Pennsylvania State University, the University of California at Davis, and other laboratories in the USA and Europe. Experiments will be conducted to measure the dissociation and mass transfer coefficients for major silage compounds. After the relationships are developed and working parameters are established, these models will be evaluated using independent data sets collected through the measurement of emissions from silos and feed bunks on dairy farms. Gaseous emissions of interest include ammonia, carbon dioxide, nitrous oxide, methane, and volatile organic compounds with particular emphasis on the anticipated most important compounds of ethanol and methanol. As models for individual compounds are developed and validated, they will be integrated in a simulation model that predicts emission levels throughout the year as a function of the feed and animal management used on the farm.
This work contributes to Objective 1 of the in-house project: Develop process-based relationships that predict emissions of ammonia, hydrogen sulfide, volatile organic compounds, and greenhouse gases from animal, feed, and manure sources on dairy farms. The objective of this subordinate project is to quantify and model the emission of important volatile organic compounds from silage. This project is a component of a national effort funded by dairy producers to develop a process-based model for estimating gaseous emissions from dairy farms and evaluating the benefits of reduction strategies.
Ethanol emission from loose corn silage and exposed silage particles was measured using wind tunnel systems to develop data for calibration and evaluation of an emission model. The emission of ethanol was highest immediately after exposing silage samples to moving air and declined by as much as 76-fold over 12 h as ethanol was depleted from the silage. Emission rate and cumulative 12 h emission increased with temperature, silage permeability, exposed surface area, and air velocity over the silage sample. An emission isolation flux chamber was also tested and found to provide inaccurate estimates of emission rates of volatile organic compounds from loose silage.
A preliminary process-based model was developed to estimate volatile organic compound (VOC) emissions from silage on farms and to assess the effectiveness of management changes on reducing emissions. Model predictions suggest that VOC emission is sensitive to environmental conditions, with the greatest emission occurring under hot and windy conditions. Predictions indicate that combined changes in storage and feeding practices can lead to substantial emission reductions. Preliminary predictions of ethanol emission for typical conditions are substantially greater than previous estimates of VOC emission from silage, but further evaluation and refinement of the model is needed to fully verify farm-level predictions. When complete, this model will provide a useful tool for evaluating strategies for reducing VOC emissions from silage.
This project is monitored through regular communication with collaborators at the University of California, Davis and the University of New Hampshire. Written progress reports are provided every six months to the funding organization.