Effects of normal and altered cattle urine on short-term greenhouse gas flux from mixed-grass prairie in the Northern Great Plains

Abstract

Use of dietary amendments to reduce nitrogen (N) in excreta represents a possible strategy to decrease greenhouse gas (GHG) emissions from livestock. In this regard, ingestion of small amounts of condensed quebracho tannin has been found to reduce N concentration in livestock urine. In this study, we sought to quantify the effects of tannin-affected cattle urine, normal cattle urine, and NH 4NO 3 in solution on greenhouse gas flux. Carbon dioxide (CO 2), methane (CH 4), and nitrous oxide (N 2O) flux was measured using static chamber methodology from the three N treatments and a no application control over a 6-week period in a mixed grass prairie in west-central North Dakota, USA. Over the course of the study, average CO 2 emission was greatest from normal urine (335 ± 8 mg C m −2 h −1) and least from the control (229 ± 19 mg C m −2 h −1), with intermediate fluxes for the tannin urine and NH 4NO 3 treatments (290 ± 27 and 286 ± 54 mg C m −2 h −1, respectively). Methane uptake was prevalent throughout the study, as soil conditions were predominantly warm and dry. Uptake of CH 4 was greatest within the control (−30 ± 2 μg C m −2 h −1) and least in the tannin urine treatment (−12 ± 4 μg C m −2 h −1). Uptake of CH 4 was over 40% less within the tannin urine treatment as compared to normal urine, and may have been repressed by the capacity of tannin to bind monooxygenases responsible for CH 4 oxidation. Average N 2O emission from NH 4NO 3 solution was more than twice that of all other treatments. Though the tannin urine treatment possessed 34% less N than normal cattle urine, cumulative N 2O emission between the treatments did not differ. Results from this study suggest the use of condensed quebracho tannin as a dietary amendment for livestock does not yield GHG mitigation benefits in the short-term.