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ARS Home » Midwest Area » St. Paul, Minnesota » Soil and Water Management Research » Research » Publications at this Location » Publication #329324
Title: Nitrous oxide fluxes and soil oxygen dynamics of soil treated with cow urine

Author
item OWENS, JEN - Lincoln University - New Zealand
item CLOUGH, TIM - Lincoln University - New Zealand
item LAUBACH, JOHANNES - Landcare Research
item HUNT, JOHN - Landcare Research
item Venterea, Rodney - Rod

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/17/2016
Publication Date: 4/20/2017
Citation: Owens, J., Clough, T., Laubach, J., Hunt, J., Venterea, R.T. 2017. Nitrous oxide fluxes and soil oxygen dynamics of soil treated with cow urine. Soil Science Society of America Journal. 81(2):289-298. doi:10.2136/sssaj2016.09.0277.

Interpretive Summary: Ruminant urine deposition onto pastures creates hot-spots where emissions of nitrous oxide (N2O) are produced by aerobic and anaerobic microbial pathways. However, limited measurements of in situ soil oxygen (O2)-N2O relationships hinder the prediction of N2O emissions from urine-affected soil. This study hypothesized that soil O2 concentration and/or relative diffusivity of O2 (Dp/Do) could explain N2O emissions from urine patches. Using a randomized plot design, N2O emissions were measured daily from a Lolium perenne L. pasture for 56 days following bovine urine deposition to an imperfectly drained silty loam soil. Soil O2, water content, water-filled pore space (WFPS), pH, conductivity and extractable nitrogen (N) and carbon (C) were measured in urine-amended and non-amended soil. Values of DP/DO were modeled. Across the urine and no urine treatments, daily mean Dp/Do explained 73% of the total variance in mean daily N2O flux, compared to 65%, <60%, and <20% for WFPS, O2, and other measured variables, respectively. Soil pH, O2, water content, WFPS and DP/DO all explained more of the variance in the urine-amended compared to the non-amended soil. Daily N2O fluxes increased substantially at DP/DO values around 0.006, which was consistent with past laboratory studies. These results demonstrate for the first time an O2 diffusion limit associated with elevated N2O fluxes in the field, occurring at Dp/Do ˜ 0.006. Further studies should examine the consistency of this critical value under varying microbial substrate and soil pH conditions. These findings will be useful in the development of improved models for predicting effects of management practices on emisions of nitrous oxide and total greenhouse gases from pastureland.

Technical Abstract: Ruminant urine deposition onto pastures creates hot-spots where emissions of nitrous oxide (N2O) are produced by aerobic and anaerobic microbial pathways. However, limited measurements of in situ soil oxygen (O2)-N2O relationships hinder the prediction of N2O emissions from urine-affected soil. This study hypothesized that soil O2 concentration and/or relative diffusivity of O2 (Dp/Do) could explain N2O emissions from urine patches. Using a randomized plot design, N2O emissions were measured daily from a Lolium perenne L. pasture for 56 days following bovine urine deposition to an imperfectly drained silty loam soil. Soil O2, water content, water-filled pore space (WFPS), pH, conductivity and extractable nitrogen (N) and carbon (C) were measured in urine-amended and non-amended soil. Values of DP/DO were modeled. Across the urine and no urine treatments, daily mean Dp/Do explained 73% of the total variance in mean daily N2O flux, compared to 65%, <60%, and <20% for WFPS, O2, and other measured variables, respectively. Soil pH, O2, water content, WFPS and DP/DO all explained more of the variance in the urine-amended compared to the non-amended soil. Daily N2O fluxes increased substantially at DP/DO values around 0.006, which was consistent with past laboratory studies. These results demonstrate for the first time an O2 diffusion limit associated with elevated N2O fluxes in the field, occurring at Dp/Do ˜ 0.006. Further studies should examine the consistency of this critical value under varying microbial substrate and soil pH conditions.