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There have been few studies examining indirect nitrous oxideemissionsassociated with nitrogen (N) leaching from agricultural soils. For agricultural drainage water,equals the water’sconcentration in excess of the atmospheric value multiplied by thetransfer velocity. Using this equation, tracers and chamber methods,andwere measured from an agricultural drain. Estimates ofwere made by measuring water speed and depth using the relationship developed by O’Connor and Dobbins [1958. Mechanisms of reaeration in natural streams. Transactions of the American Society of Civil Engineers. 123:641–684]. The measurements and estimates were not significantly different andaveraged 5 m d−1. Alternatively, for the method developed by the Intergovernmental Panel on Climate Change,equals the mass of N flowing in the water multiplied by an emission factor (EF). By additional measurements of the drain’s width, the water’s flow rate and nitrate () concentration, the estimated EF was 1.2 × 10−4 kgkg−1. [ABSTRACT FROM PUBLISHER]

Nitrous oxide (N 2 O) is a potent greenhouse gas and a precursor to compounds which deplete stratospheric ozone. Agricultural soils are the principal anthropogenic N 2 O source, which includes urine patches of cattle fed by grazing pasture. While such N 2 O emissions can be measured, involved time and space scales are usually only minutes and metres, respectively. Nevertheless, climate change stakeholders need large-scale national emissions over time to construct annual N 2 O emissions inventories for international treaty compliance requirements. We have developed a mathematical model to bridge the gap between measurement and stakeholder requirements for N 2 O emissions from grazing cattle urine patches. Our methodology begins with the emissions from a patch. Convolution integrals are then used to spatially and temporally scale the emissions from discrete grazing events to paddock, farm and region levels across the year. The model developed shows how the emissions are smoothed out with scaling and the implications from the scaling. [ABSTRACT FROM AUTHOR]

Between 11 May 2000 and 31 January 2013, 185 field trials were conducted across New Zealand to measure the direct nitrous oxide (N2O) emission factors (EF) from nitrogen (N) sources applied to pastoral soils. The log(EF) data were analysed statistically using a restricted maximum likelihood (REML) method. To estimate mean EF values for each N source, best linear unbiased predictors (BLUPs) were calculated. For lowland soils, mean EFs for dairy cattle urine and dung, sheep urine and dung and urea fertiliser were 1.16 ± 0.19% and 0.23 ± 0.05%, 0.55 ± 0.19% and 0.08 ± 0.02% and 0.48 ± 0.13%, respectively, each significantly different from one another (p < 0.05), except for sheep urine and urea fertiliser. For soils in terrain with slopes >12°, mean EFs were significantly lower. Thus, urine and dung EFs should be disaggregated for sheep and cattle as well as accounting for terrain. [Copyright &y& Elsevier]

Abstract: Dicyandiamide (DCD, C2H4N4) is a nitrification inhibitor that has been studied for more than 80 years. However, there are few papers that have examined the use of DCD on dairy farms where cattle graze pasture and where urine is the primary form of nitrogen (N) deposited onto soils. After DCD was applied (10kgDCDha−1) with bovine urine (700–1200kgNha−1) to five soils throughout New Zealand, the reduction in direct nitrous oxide (N2O) emissions was significant and remarkably consistent (71±8%, average±standard error). The application of DCD to these soils occurred in autumn and winter; daily average soil temperature (T) was reported but these data were not further analysed. Perusal of the literature suggested no consensus on the temperature dependence of DCD degradation in soils. Based on published data from controlled-environment studies of soils sampled in four countries, we quantified the relation between T and the time for DCD concentration in soils to decline to half its application value (t ½) as t ½ (T)=168e−0.084T with parameter standard errors of ±16d and ±0.011d−1, respectively (n =16). For example, at 5°C a 1°C increase in T reduced t ½ from 110 to 101d whereas at 25°C the reduction was 20–19d. Analysing T data from the New Zealand trials using our t ½ (T) function, over 43–89d when direct N2O emissions from treated plots became indistinguishable from the controls, the estimated percentage of applied DCD remaining in the soil averaged 43±10%. These calculations suggested the apparently remaining DCD was ineffective with respect to direct N2O emissions. In the absence of measurements, explanations for this interpretation included vertical displacement of the DCD and sorption onto organic matter in soils. The consistent DCD efficacy from these trials corresponded with T generally <10°C, so it is suggested as an application criteria for the reduction of direct N2O emissions from pastoral soils subjected to urine excretion by grazing cattle. [Copyright &y& Elsevier]

Abstract: Nitrous oxide research has generally focused directly on measuring fluxes of N2O from the soil surface. The fate of N2O in the subsoil has often been placed in the ‘too hard’ basket. However, determining the production, fate and movement of N2O in the subsoil is vital in fully understanding the sources of surface fluxes and in compiling accurate inventories for N2O emissions. The aim of this study was to generate and introduce into soil columns 15N labelled N2O, and to try and determine the consumption of the 15N2O and production of ambient N2O. Columns, 100cm long by 15cm diameter, were repacked with sieved soil (sampled from 0 to 5cm depth) and instrumented with silicone rubber gas sampling ports. Nitrous oxide enriched with 15N was generated using a thermal decomposition process at 300°C and then transferred to 2l flasks. After equilibrating with SF6 tracer gas the 15N2O was introduced into the soil columns via passive diffusion. Gas samples from the soil profile and headspace flux were taken over a 12-day period. A watering event was simulated to perturb the 15N2O gas composition in the soil profile. Using the measured 15N enriched fluxes and the rate of decline in 15N in the N2O reservoir, from which the N2O diffused into the soil, we calculated an N2O sink (consumption plus absorption by water) equal to 0.48ng N2O g−1 soil h−1. The decrease in the 15N enrichment between successive soil depths indicated N2O production in the soil profile and we calculated a net N2O production rate of 0.88ng N2O g−1 soil h−1. This pilot study demonstrated the potential for simultaneously measuring both N2O consumption and production rates, using the 15N enrichment of the N2O measured. Further potential refinements of the methodology are discussed. [Copyright &y& Elsevier]