Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/28/2011
Publication Date: 9/1/2011
Publication URL: http://handle.nal.usda.gov/10113/53875
Citation: Powell, J.M., Aguerre, M.J., Wattiaux, M.A. 2011. Dietary crude protein and tannin impact dairy manure chemistry and ammonia emissions from soils. Journal of Environmental Quality. 40:1767-1774. DOI:10.2134/jeq2011.0085. Interpretive Summary: In the past, many dairy farmers fed high levels of dietary protein as a risk management strategy to avoid the chance of milk production drops. More recently, research has shown that feeding excess protein reduces feed nitrogen use efficiency with the excess nitrogen being excreted as urea nitrogen; this, in turn, increases ammonia emissions from dairy farms and thereby heightens human health and environmental concerns. Research has also shown that tannins (a naturally occurring compound used to cure leather) improve feed nitrogen use efficiency. So we conducted two studies to determine if feeding less crude protein and more tannin to dairy cows would reduce urine excretion and ammonia emissions after slurry (semi-liquid manure) application to soils. Emissions from slurry from a high crude protein diet were 1.5 to 2.6 times greater than from slurry from a low crude protein diet. Emissions from slurry containing tannin were 28% to 49% lower than emissions from slurry containing no tannin. Larger scale and longer term field trials are needed to ascertain effectiveness of tannin in abating ammonia loss from land-applied slurry and in conserving the fertilizer nitrogen value of dairy slurry.
Technical Abstract: Excess crude protein (CP) in dairy cow diets is excreted mostly as urea nitrogen (N), which increases ammonia (NH3) emissions from dairy farms, and heightens human health and environmental concerns. Feeding less CP and more tannin to dairy cows may enhance feed N use and milk production, abate NH3 emissions and conserve the fertilizer N value of manure. Lab-scale ventilated chambers were used to evaluate impacts of CP and tannin feeding on slurry chemistry, NH3 emissions and soil inorganic N levels after slurry application to a sandy loam soil and a silt loam soil. Slurry from lactating Holstein dairy cows (Bos taurus) fed two levels (g kg-1) of dietary CP: 155 (LCP) and 168 (HCP) each fed at four levels (g kg-1) of dietary tannin extract [a mixture from red quebracho (Schinopsis lorentzii) and chestnut (Castanea sativa) trees]: 0 (0T), 4.5 (LT), 9.0 (MT) and 18.0 (HT) were applied to soil-containing lab-scale chambers, and NH3 emissions were measured 1, 3, 6, 12, 24, 36 and 48 h after slurry applications. During the 3 h to 48 h measurements periods, NH3 emissions from the HCP slurry were 1.5 to 2.6 times greater than from the LCP slurry. At trial’s end (48 h) however concentrations of inorganic N in soils were greater in HCP slurry-amended soils than in LCP-amended soils. Emissions from HT slurry were 28% to 49% lower than emissions from 0T slurry during the 24-h to 48-h measurements, yet these differences did not impact soil inorganic N levels. Cumulative NH3 emissions from the sandy loam soil were 1.1 to 1.2 times greater than from silt loam soil, a result which decreased soil inorganic N in the sandy loam compared to the silt loam soil. Larger scale and longer term field trails are needed to ascertain effectiveness of tannin extracts in abating NH3 loss from land-applied slurry, and the impact of tannin-containing slurry on soil N cycles.