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Title:   Author  item
                                            OWENS, JEN - Lincoln University - New Zealanditem
                                            CLOUGH, TIM - Lincoln University - New Zealanditem
                                            LAUBACH, JOHANNES - Landcare Researchitem
                                            HUNT, JOHN - Landcare Researchitem
                                            Venterea, Rodney

                                                         - *Rod*item
                                            PHILLIPS, REBECCA - Landcare Research
  Submitted to: Journal of Environmental Quality
                                    Publication Type: Peer Reviewed Journal
                                    Publication Acceptance Date: 2/10/2016
                                    Publication  Date: 7/7/2016
                                    Citation: Owens, J., Clough, T., Laubach, J., Hunt, J., Venterea, R.T., Phillips, R. 2016. Nitrous oxide fluxes, soil oxygen, and dentrification potential from urine and non-urine treated soil under different irrigation frequencies. Journal of Environmental Quality. 45:1169-1177.Interpretive Summary: Despite increased use of irrigation to improve forage quality and quantity for grazing cattle, few studies have assessed how irrigation practices influence nitrous oxide (N2O) emissions from urine-impacted soils. In particular, irrigation effects on soil oxygen (O2) availability, one of the major controllers of N2O flux, are poorly understood. It was hypothesized that increased irrigation frequency would result in lower N2O emissions as a result of decreased O2 concentrations favoring greater N2O reduction to dinitrogen (N2). We examined effects of high (3-d) versus low (6-d) irrigation frequency, both with and without bovine urine addition to pasture, on daily N2O fluxes over 35 days. Soil O2, temperature and water content were continuously measured at multiple depths, and inorganic nitrogen, organic carbon, soil pH were measured at 6-d intervals. Measurements of denitrification enzyme activity (DEA) with and without acetylene inhibition were used to infer the N2O/(N2O+N2) ratio. The N2O/(N2O+N2) ratio was lower under high- compared to low-frequency irrigation, suggesting greater potential for N2O reduction to N2 with more frequent irrigation. However, while N2O fluxes were increased by urine addition, they were not affected by irrigation frequency. Soil O2 decreased temporarily after urine deposition, but O2 dynamics did not explain N2O dynamics. Relative gas diffusivity (DP/DO) was a better predictor of N2O fluxes than O2 concentration. On a free draining soil, increasing irrigation frequency, while providing the same total water volume, did not enhance N2O emissions under ruminant urine patches in a grazed pasture. These results will be useful to producers, scientists and regulators interested in developing improved irrigation management practices.
                                Technical Abstract: Despite increased use of irrigation to improve forage quality and quantity for grazing cattle (Bos taurus), few studies have assessed how irrigation practices influence nitrous oxide (N2O) emissions from urine-impacted soils. In particular, irrigation effects on soil oxygen (O2) availability, one of the major controllers of N2O flux, are poorly understood. It was hypothesized that increased irrigation frequency would result in lower N2O emissions as a result of decreased O2 concentrations favoring greater N2O reduction to dinitrogen (N2). We examined effects of high (3-d) versus low (6-d) irrigation frequency, both with and without bovine urine addition to pasture, on daily N2O fluxes over 35 days. Soil O2, temperature and water content were continuously measured at multiple depths, and inorganic nitrogen, organic carbon, soil pH were measured at 6-d intervals. Measurements of denitrification enzyme activity (DEA) with and without acetylene inhibition were used to infer the N2O/(N2O+N2) ratio. The N2O/(N2O+N2) ratio was lower under high- compared to low-frequency irrigation, suggesting greater potential for N2O reduction to N2 with more frequent irrigation. However, while N2O fluxes were increased by urine addition, they were not affected by irrigation frequency. Soil O2 decreased temporarily after urine deposition, but O2 dynamics did not explain N2O dynamics. Relative gas diffusivity (DP/DO) was a better predictor of N2O fluxes than O2 concentration. On a free draining soil, increasing irrigation frequency, while providing the same total water volume, did not enhance N2O emissions under ruminant urine patches in a grazed pasture.


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