PSXI-25 The effect of plant tannins on methane and nitrous oxide emissions from dairy manure under laboratory conditions

Abstract Emissions of greenhouse gases (GHG; methane, CH4; nitrous oxide, N2O) from dairy cattle manure contribute to global climate change. The aim of this study was to assess the associative effects of three different levels [0, 4 and 8% wet weight (WW) basis] of condensed tannins (CT; quebracho tannins) and hydrolysable tannins (HT; chestnut tannins) on CH4 and N2O emissions. The dairy manure consisted of a 50:50 volume mixture of fresh feces and dry manure scraped from the surface of an open-lot dairy in the Texas panhandle. Control (0% tannin), 4%, and 8% of CT or HT (w/w) were added to each bucket and homogenized with a hand mixer for 5 min. Aliquots of 220 g (WW) manure, with or without tannins, were placed into 1 L fermentation bottles (n = 3, total of 18 bottles) and incubated at 39o C for 14 days. A second set of 18 fermenters were set up in the same manner for sample collection at 0, 2, 3, 6, and 9 h to discern changes in pH and redox status. There were no differences in redox values with the addition of either tannin type to in vitro fermenters. However, application of CT to dairy manure reduced (P < 0.05-0.01) cumulative CH4 emissions by 68 to 63% at the concentrations of 4 and 8% WW, respectively, compared with the non-tannin control group. Both CT and HT decreased cumulative N2O emissions (P < 0.02). Examination of the emission kinetics revealed a tradeoff (interchange or pollution swapping) between CH4 and N2O emissions when tannins were applied to manure. These results suggested that the inclusion of 4% CT (WW) is a promising technique for reducing CH4 and N2O emissions from excreted dairy manure. Further study is warranted to investigate the effects of feeding CT and HT on manure-derived GHG in dairy systems.