Determination of silage face surface area on commercial California dairy farms

Analysis of exposed silage face surface area was conducted to better understand and provide feed management recommendations as well as evaluate potential compliance needs related to volatile organic compound emissions. Policy was developed by the San Joaquin Valley Air Pollution Control District (District) to restrict exposed surface area of silage piles to 199·7 m² per farm if only one pile was exposed or 399·5 m² per farm if more than one pile was exposed. Exposed surface area on piles of silages at 20 dairies was quantified to determine impacts of these surface area restrictions. Herd size ranged from 490 to 7,200 milking cows, and the number of exposed piles ranged from one to four per farm as maize and/or wheat silage. Surface area of piles was quantified based on pile measurements and geometric shapes. The measured value was compared to the estimated value using the District ‘online calculator’. The District calculator used inputs for base length and height with assumed constant relationships between base and top lengths. Five of 43 piles had >199·7 m² of exposed surface area. Sixteen of 20 dairies with more than one exposed surface complied with the exposed surface area restriction. On average, the District calculator overestimated surface areas by 11·6% ± 14·8 (range ?57·7 to 38·4%). Pile measurements and use of geometric shapes provide a more precise method to quantify exposed surface area. This will be of particular use for those operators who utilize the District calculator and find their exposed areas out of compliance.