Silage pile shrink losses not nearly as great as regulators thought

California air regulators were convinced that volatile fatty acid losses from silage piles in the state’s San Joaquin Valley were large enough to impact air quality in the valley.

No one can argue that air quality in the Central Valley is a problem certain times of the year, because Pacific air currents aren’t strong enough to move air over the 11,000’ to 14,000’  Sierra Mountains that border the valley to the east. But regulators in the San Joaquin Valley Air Pollution Control District were convinced that the mountains of silage needed to feed hundreds of thousands of cows were a big contributor to air issues. SJVAPCD regulators were expecting losses of 20 to 25%.

So in 2013 and 2014, Peter Robinson and his colleagues at the University of California-Davis undertook an in-depth study of emissions, measuring shrink losses from silage piles on seven farms. They did multiple samples from the face of the silage piles at various depths and then measured and calculated shrink.

Robinson notes that all of the silage piles were built using best management practices, and packing densities were 44 lb./cu/ft or more in corn silage piles. The densities in cereal grain piles were 40 lb. or more.

The bottom line results: “The extent of silage shrink pollution is much smaller than expected,” says Robinson. After all the measurements were done, volatile fatty acid losses averaged about 3% from corn silage piles and about 3.5%  from winter wheat and triticale silage.  The losses from winter wheat and triticale piles were higher because it is more difficult to maintain a smooth face when removing material from these piles, allowing more air penetration, says Robinson.

He adds that results would likely be similar in the Midwest, and perhaps even less, if freezing occurs during feed out. That’s because the freezing would help seal the face of the pile and prevent emissions from occurring.

The good news is that air regulators have accepted the results of the study, and for the most part, no longer consider silage piles major sources of air pollution. The bad news is that they have now moved on to methane emissions from cows and manure storage at their next target for regulations.

Robinson presented his finding here at World Dairy Expo in Madison, Wis., this week.