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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]

Highlights: [•] Dicyandiamide (DCD) degradation rate and mean soil temperature were linearly related. [•] At 8 and 16°C, estimated DCD half-lives were 39±6 and 25±3 days, respectively. [•] At a temperature, DCD degraded faster in soils in the field than in incubated samples. [ABSTRACT FROM AUTHOR]

Abstract: For sixty years at Winchmore, South Island, New Zealand (43°48′S, 171°48′E, 160 masl), stoney soils under continuous pasture grazing by sheep have received rainfall (nil irrigation) or rainfall and irrigation as required during summer. This consistently managed, replicated field trial presents a unique opportunity to examine long-term treatment effects on pastoral soil. Samples were recently excavated at intervals to a depth of 1m and the total carbon (C) storage measured. In the irrigated plots, soil C storage (9.1±0.3kgCm−2, mean±standard error, n =3) was significantly less (p <0.05) than in plots receiving rainfall alone (13.4±0.8kgCm−2). We estimated irrigation induced a 36% increase of C inputs to the soil on an annual basis, mostly as litter fall. Using a respiration model based on soil temperature and water content inputs, irrigation was also estimated to have induced a 97% increase in rate of annual C loss to the atmosphere. On this basis, the estimated irrigation effects had reduced C storage by 61% (97–36%), reasonably accounting for the 47% treatment effect determined by soil sampling. [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: In New Zealand, the principal source of methane emissions to the atmosphere () is ruminant animals, up to ca. 85million sheep and cattle fed by year-round outdoor grazing on pasture. Uncertainty analysis is developed for a change in from 1 year to another (). For 1990 and 2003, annual averaged 1036Gg and was 88±52Gg with 95% certainty that was due to a true increase of emissions. The standard error was largely attributed to uncertainty in estimating pasture herbage consumption from the animal''s energy requirements for maintenance and production. [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]

For 212 days, including a 117-day-long summer drought with only 45 mm rainfall, fluxes of latent and sensible heat (λE and H, respectively) and carbon dioxide (CO2) were measured by eddy covariance over a tussock grassland in New Zealand. The measurement site was grazed and now has a low leaf area index (∼0.5), dominated by the invasive weed Hieracium, and has a high proportion of bare soil (43%). Energy balance closure was excellent (0.97H+λE)−9 (W m−2)=Ra, r2=0.93, n=8407 half-hourly averages and Ra is the available energy. As the drought progressed, the daily average Bowen ratio (H/λE) increased from 1 to 15 which corresponded with increasing air and surface temperatures and vapour pressure deficit. Maximum evaporation rate was 3.8 mm per day and it averaged 1.1 mm per day, seasonally equivalent to 93% of the rainfall (241 mm) in accordance with mass conservation, but only 47% of the equilibrium evaporation rate. It was estimated that 50% of soil water was utilised before water deficit began to limit λE and, on average, the evaporative fraction λE/Ra declined exponentially with time after rainfall from 0.43 to 0.05 in 15 days.Maximum net carbon dioxide uptake (denoted negative) and efflux (respiration) rates (Re) were −5 and 2 μmol m−2 s−1, respectively. These rates are much less than those for grasslands elsewhere. Soil respiration rate and temperature were exponentially related when water was plentiful, but at the same temperature, respiration declined by a factor of 4 as water content ranged from 0.21 (field capacity) to 0.04 m3 m−3. Soil respiration responded to drought-breaking rainfall and irrigation with a return to maximum rates within 1 day.During spring, when soil water content was >0.10 m3 m−3 (October and November), the daily CO2 flux density (FCO2) was relatively conservative at −1.2 g C m−2 per day. During drought (January–February), the ecosystem became a carbon source with a mean emission flux of 0.70 g C m−2 per day. Twenty days after a drought-breaking rainfall, the ecosystem returned to being a net sink, but by this time the mean daily air temperature was falling and the first frost of the winter (9 April; −1.8 °C) had occurred thus reducing the ability of the ecosystem to respond to the increased soil water content. Water availability severely limits the carbon acquisition of this ecosystem with the result that during summer, net productivity is closely related to both the frequency and the timing of rainfall events. During summer droughts the inter-montane-basin tussock grasslands may be carbon neutral. [Copyright &y& Elsevier]

Investigates the exchange of carbon dioxide between an undisturbed old-growth forest and the atmosphere. Determination of how environmental factors regulate ecosystem gas exchange; Association of daytime exchange variation to changes in photosynthetically active photon flux density; Implications for the development of diurnal exchange models.

Demonstrates that the turbulent nature of the atmosphere affects plant processes. Factors influencing plant water use and transport; Spectral analysis of tree sap; Correlation of sap flux variations between trees of the same or different strata in an undisturbed forest; Atmospheric specific humidity and temperature fluctuations.

Abstract We have investigated the effect of supercritical drying (SD) on the porosity and the BET-N 2 specific surface area (SSA) of five allophane-rich and three non-allophanic topsoils. The contribution of organic matter (OM) and short-range ordered (SRO) constituents to the nanoscale porosity (<100 nm size) and SSA was also evaluated following chemical treatments to oxidise OM and then remove the SRO phase. The average pore volume and SSA of the soils, measured after SD, are greater than the values obtained after air drying. For soils that are rich in SRO constituents, oxidation of OM leads to an increase in SSA. This observation is attributed to the unblocking of pore necks previously covered by OM, while the subsequent removal of SRO constituents causes a sharp decrease in SSA. The SRO constituents containing oxalate-extractable Al, are the major contributors to the SSA of the inorganic fraction. Besides confirming that SD can help preserve the nanoscale porosity of allophane-rich soils, the results highlight the contribution of SRO constituents to the SSA of soils and their ability to accumulate OM. Highlights • Controlled supercritical drying (SD) of soils facilitates dehydration while preserving structure. • In allophane-rich soils, SD preserved mesoporosity and specific surface area (SSA). • SSA increased after removal of organic matter uncovering mineral surfaces. • Removal of short-range ordered constituents decreased pore volume and SSA. [ABSTRACT FROM AUTHOR]

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]

Following advances with methods for 13C/12C isotopic analysis of methane in small (&les;4 L) air samples, new isotope dilution techniques are proposed for measurement of methane emissions at the paddock scale from grazing ruminant animals. These techniques combine measurement of the isotopic δ13CH4 composition of air samples with a non-intrusive mass balance method applied in the nocturnal boundary layer. Flux estimates from trials using the isotope dilution techniques are compared with estimates based on scaling up individual animal emission measurements using a rumen gas tracer technique. The methane flux assessed by the latter technique ranged from 35 to 70 mg (CH4) m−2 d−1 with a stocking density between 10 and 20 sheep ha−1. The isotope dilution based nocturnal boundary-layer estimates generally agreed to better than a factor of 2 and usually to within 20% of the average of individual animal emission rate per unit area of paddock. Both static and advecting mass balance methods are developed. In the advecting case, the upwind/downwind contrast in δ13C was typically 0.2–0.5‰. Care was necessary with air sampling to avoid error in this small contrast contributing to error in the flux. Agreement between concentration- and isotope-based nocturnal boundary layer methods and the sheep breath measurements indicated that sample representativeness was generally good. Factors which affect the accuracy of the method are examined and include variability in nocturnal mixing height, the assumed δ13CH4 composition of the source sheep breath and diurnal patterns in sheep emission. This paper establishes new techniques useful in the paddock to landscape scale although widespread application awaits further development of technology for rapid and repeatable field analysis of δ13CH4 in small samples. [Copyright &y& Elsevier]