The extent to which the wetted soil area of a urine patch influences surrounding pasture is relatively unknown. The study objective was to use N-15 tracer to quantify pasture N uptake in the wetted' and periphery areas of a spring deposited bovine urine patch over 311 days. Ruminant N-15 enriched urine was applied to soil creating a circular wetted area, zone A' (800kgNha(-1)), with and without urea fertiliser (35kgNha(-1)). Pasture yields, N-15 recovery and soil inorganic-N dynamics were monitored from zone A and two peripheral zones, B and C. Fertiliser had no effect on cumulative urinary N-15 recovery in pasture (50%-52%). Average cumulative pasture N-15 recovery in zones A, B and C were 30.6%, 17.3% and 4.2%, respectively. Soil inorganic-N-15 recovery occurred in zones A and B, declining with distance from the wetted area. The results suggest an effective urine patch area of 0.95m(2) or 3.4 times the wetted area.

Ruminants excrete as much as 70-95% of the nitrogen (N) they consume. The urine patch is the conduit through which much of this N is recycled in grazed pasture systems. This chapter focuses on three key areas: urine patch characteristics and N cycling processes; implications for N cycling at the farm and paddock scale; and strategies available to mitigate N losses from the urine patch. The urine patch N loading rate is a key metric for quantifying and modeling fate of N; yet it is a derived value, relying on estimates of urine volume and N concentration, and the urine patch surface area, all of which are variable. Much is known about N cycling processes in the urine patch but further understanding of N loss, leaching of dissolved organic N, and mineralization-immobilization turnover is needed. Typical values (as a percentage of the deposited urinary N) were estimated as: 13% ammonia volatilization; 2% nitrous oxide emission; 20% nitrate leaching; 41% pasture uptake; 26% gross immobilization. The relative importance of each process is influenced by urine patch characteristics and environmental factors. Models are an important tool for scaling from the individual urine patch to the paddock and farm scale, though accounting for variability in urine patch characteristics, and spatial and temporal distribution, remains a challenge. Many potential management strategies to decrease N loss from the urine patch are still at the proof of concept stage with few actually deployed on the farm. Further research is required to integrate these into farm management systems.

Significant areas of ruminant-grazed pastures are simultaneously covered by excreted urine and fertiliser nitrogen (N). However, the effect of overlapping N inputs on nitrous oxide (N2O) emission factors has not been studied. Three rates of N-15-labelled urea fertiliser were applied with either no urine, an autumn-urine or a spring-urine application. These treatments were applied to perennial ryegrass pasture (Lolium perenne L.) and N2O fluxes were determined over 373 days using standard static closed chamber techniques. Cumulative N2O-N fluxes ranged from 766 to 4332 g N2O-N ha(-1) (0.36%-0.74% of total N applied) and were lowest in the absence of urine; however, no fertiliser rate effect occurred regardless of urine presence or season of application. Urine-elevated N2O-N fluxes followed urine applications for up to 40 days, resulting in lower fertiliser contributions to the N2O-N fluxes at these times. Total N-15 recoveries as N2O-N were 0.04% and did not differ with fertiliser rate.

Urine patches are the primary source of N loss from pastoral systems due to the high N loading that occurs over a relatively small area. However, few studies have sought to determine the effect of concurrently deposited urine and fertiliser on the fate of N in pastoral systems, even though the application of fertiliser soon after grazing is commonly practised, while no studies have examined seasonal effects of any interaction.The objective of this study was therefore, to understand how the combination of fertiliser-N and urine affected fertiliser-associated NO3- leaching losses and plant uptake of N. A two year lysimeter study was undertaken with urine (800 kg N ha(-1)) applied in either autumn or spring. Urea fertiliser enriched with N-15 was applied to these lysimeters at rates equivalent to 200 or 400 kg N ha(-1) per year according to the standard regional practice.Urine and fertiliser at the 400 kg N ha(-1) rate increased total NO3- leaching by up to 58 kg ha(-1) (P<0.001), from urine applied in either autumn or spring. Fertiliser applied at 200 kg N ha(-1) did not increase N leaching from urine patches. Fertiliser N-15 recovery in drainage was <2.2% and was not affected by fertiliser rate. Pasture uptake accounted for up to 52% of the fertiliser N-15 recovery and this increased with increasing fertiliser rates, even in the presence of urine. Recovery of fertiliser N-15 in the soil at the end of the experiment averaged 22% with the majority of this in the top 10 cm soil.These results indicate that the potential for leaching of fertiliser N, applied to a urine patch, is low, and that avoiding fertiliser application over urine patches, reduces leaching losses of fertiliser-N by <2%, which is minimal in terms of total N loss mitigation. However, at high fertiliser application rates to urine patches (i.e. 400 kg N ha(-1)), the total N leaching from non-fertiliser (non N-15-enriched) sources can increase. Further work is required to quantify these effects at the paddock scale. The results also show that NO3- leaching losses were greater from autumn applied urine compared to spring applied urine by up to 306 kg NO3--N ha(-1). (C) 2015 Elsevier B.V. All rights reserved.

When debating the performance of models such as Overseer‟s ability to estimate whole-farm nutrient losses, four terms are often used almost interchangeably: accuracy, precision, error and uncertainty. However, the terms are not interchangeable and it is important to consider the implications of the commonly used terminology, in the context of this farm-scale nutrient budgeting model. Given that it is not usually practicable to directly measure whole-farm nutrient losses, use of the terms accuracy or error are not directly applicable, because there is no true value to compare an estimate with. Model uncertainty is the most relevant applicable term for annual whole-farm nutrient loss estimates. Model uncertainty will be greatest for conditions where there are no, or few, data for calibration and validation. Precision in the context of Overseer is about precision of input information.

of a thesis submitted in partial fulfilment of the requirements for the Degree of Doctor of Philosophy Abstract The interactive effects of nitrogen fertiliser and animal urine on nitrogen efficiency and losses in New Zealand dairy farming systems. by Laura E. Buckthought The loss of nitrogen (N) through nitrate (NO3) leaching and nitrous oxide (N2O) emissions from pastoral dairy systems is one of the largest challenges facing the New Zealand agricultural industry. Nitrate leaching contributes to nutrient enrichment and accelerated eutrophication of streams, lakes and estuaries, while N2O is both a greenhouse gas and the dominant anthropogenic emission contributing to stratospheric ozone depletion. Urine patches are the primary source of N loss from pastoral systems due to the high N loading that occurs over a relatively small area. Excessive or inappropriately timed fertiliser applications can also add to N loss. Few studies have sought to determine the effect of concurrently deposited urine and fertiliser on the fate of N in pastoral systems, even though the application of fertiliser soon after grazing is commonly practised, while no studies have examined seasonal effects of any interaction. It is generally assumed that fertiliser applied over a urine patch will simply exacerbate the total N losses, as the urine-N saturates plant-N utilisation rates in pasture. This study, therefore, aimed to quantify the additional losses (if any) that occur as a result of fertiliser being applied concurrently onto a urine patch, and furthermore, determine the fate of the fertiliser N within the urine patch. To determine this, a two year lysimeter study was undertaken where urine patches were applied in either autumn or spring. Urea fertiliser enriched with 15N was applied to these lysimeters at rates of either 200 or 400 kg N ha-1 according to the standard regional practice. The amount of fertiliser derived N was measured in the leachate, N2O emissions, pasture and soil. Fertiliser 15N recovered in leachate and N2O emissions was <2.2% and <0.1%, respectively. Urine and fertiliser at the 400 kg N ha-1 rate did increase total NO3 leaching by up to 55 kg ha-1 (p < 0.001), but this was as unlabelled N. Pasture uptake accounted for up to

Recently the Intergovernmental Panel on Climate Change (IPCC) emission factor EF5-r was revised downward to a value of 0.0025 kg N₂O-N per kg NO₃-N leached. It was not reduced further due to the continued uncertainty surrounding the dynamics of N₂O in river systems. There have been few studies where river system N₂O yields and fluxes have been measured. In this study, we examined the relationship between NO₃-N and N₂O-N fluxes at 10 sites along a braided river system (84 km) over a 397-d period. Isotopic analysis of NO₃-N river water samples and the potential agricultural nitrogen (N) sources demonstrated that the NO₃-N came from agricultural or sewage sources. Percent saturation of N₂O varied with site and date (average, 114%) and correlated with river N₂O-N concentrations. Modeled N₂O fluxes (16-30 μg m(-2) h(-1)) from five sites were strongly related to river NO₃-N concentrations ( r² = 0.86). The modeled N₂O-N fluxes ranged from 39 to 81% of the IPCC-derived emissions based on the NO₃-N load in the river over 397 d and do not support further lowering of the EF5-r. Further in situ river studies are required to verify the N₂O-N fluxes and the calculated gas transfer velocity values for these braided river systems.

Previous laboratory studies have demonstrated that hippuric acid, a ruminant urine constituent, can mitigate nitrous oxide (N2O) emissions from simulated urine patches. Hippuric acid has the potential to be a N2O mitigation tool because animal diets can be manipulated to adjust its concentration in the urine. This study was conducted to determine if the effect observed in previous laboratory studies would also occur in situ under field conditions. In our field study, plots were treated with unadulterated bovine urine (56 mM hippuric acid), the same bovine urine amended with either benzoic acid (34 mM), dicyandiamide (DCD) or varying rates of hippuric acid (up to 90 mM). Soil inorganic-N, N2O fluxes, and plant N responses were monitored over a 78 d period. Effects on microbial communities were monitored by determining the size and structure of nitrite oxidizer (nxrA) and nitrite reducer (nirS) bacterial populations using real-time PCR and denaturing gradient gel electrophoresis (DGGE), respectively. Decreases in N2O emissions, with increasing hippuric and benzoic acid concentrations, were only seen on Day two of the trial. With the exception of the DCD treatment (0.60% of N applied) the amended urine treatments did not significantly affect emissions of N2O as a percentage of N applied (1.28–1.65%). Soil inorganic-N and plant response were not affected by urinary amendment, except in the DCD treatment where nitrification inhibition occurred. Nitrite oxidizer community structures shifted and increased approximately 5.4-fold in size over 48 d in response to urine, although no specific response to elevated hippuric acid or benzoic acid was observed. No treatment effects were observed on community structure of the nitrite reducing bacteria but averaged over time the highest rate of hippuric acid significantly decreased nirS gene copy numbers g−1 soil. We concluded that under the conditions of this field study, increasing hippuric or benzoic acid concentrations in bovine urine had no effect on N2O mitigation in situ. We argue that the discrepancy with previous laboratory studies may be related to differences in soil pH, microbial communities and the presence of vegetation. Further research is needed to determine the potential for hippuric acid as a tool to mitigate N2O emissions, and its effect(s) on resident N cycling microorganisms.

There is uncertainty in the estimates of indirect nitrous oxide (N2O) emissions as defined by the Intergovernmental Panel on Climate Change (IPCC). The uncertainty is due to the challenge and dearth of in situ measurements. Recent work in a subtropical stream system has shown the potential for diurnal variability to influence the downstream N transfer, N form, and estimates of in-stream N2O production. Studies in temperate stream systems have also shown diurnal changes in stream chemistry.The objectives of this study were to measure N2O fluxes and dissolved N2O concentrations from a spring-fed temperate river to determine if diurnal cycles were occurring. The study was performed during a 72 h period, over a 180 m reach, using headspace chamber methodology. Significant diurnal cycles were observed in radiation, river temperature and chemistry including dissolved N2O-N concentrations. These data were used to further assess the IPCC methodology and experimental methodology used. River NO3-N and N2O-N concentrations averaged 3.0 mg L-1 and 1.6 mu g L-1, respectively, with N2O saturation reaching a maximum of 664%. The N2O-N fluxes, measured using chamber methodology, ranged from 52 to 140 mu g m(-2) h(-1) while fluxes predicted using the dissolved N2O concentration ranged from 13 to 25 mu g m(-2) h(-1). The headspace chamber methodology may have enhanced the measured N2O flux and this is discussed. Diurnal cycles in N2O% saturation were not large enough to influence downstream N transfer or N form with variability in measured N2O fluxes greater and more significant than diurnal variability in N2O% saturation. The measured N2O fluxes, extrapolated over the study reach area, represented only 6 x 10(-4)% of the NO3-N that passed through the study reach over a 72 h period. This is only 0.1% of the IPCC calculated flux.

There is uncertainty in the estimates of indirect nitrous oxide (N2O) emissions as defined by the Intergovernmental Panel on Climate Change (IPCC). The uncertainty is due to the challenge and dearth of in situ measurements. Recent work in a subtropical stream system has shown the potential for diurnal variability to influence the downstream N transfer, N form, and estimates of in-stream N2O production. Studies in temperate stream systems have also shown diurnal changes in stream chemistry. The objectives of this study were to measure N2O fluxes and dissolved N2O concentrations from a spring-fed temperate river to determine if diurnal cycles were occurring. The study was performed during a 72 hour period, over a 180 m reach, using headspace chamber methodology. Significant diurnal cycles were observed in radiation, river temperature and chemistry including dissolved N2O-N concentrations. These data were used to further assess the IPCC methodology and experimental methodology used. River NO3-N and N2O-N concentrations averaged 3.0 mg L and 1.6 μg L respectively, with N2O saturation reaching a maximum of 664%. The N2O-N fluxes, measured using chamber methodology, ranged from 52-140 μg m h while fluxes predicted using the dissolved N2O concentration ranged from 13-25 μg m h. The headspace chamber methodology may have enhanced the measured N2O flux and this is discussed. Diurnal cycles in N2O % saturation were not large enough to influence downstream N transfer or N form with variability in measured N2O fluxes greater and more significant than diurnal variability in N2O % saturation. The measured N2O fluxes, extrapolated over the study reach area, represented only 6x10 percent of the NO3-N that passed through the study reach over a 72 h period. This is only 0.1% of the IPCC calculated flux

There is uncertainty in the estimates of indirect nitrous oxide (N O) emissions as defined by the Intergovernmental Panel on Climate Change (IPCC). The uncertainty is due to the challenge and dearth of measurements. Recent work in a subtropical stream system has shown the potential for diurnal variability to influence the downstream N transfer, N form, and estimates of in-stream N O production. Studies in temperate stream systems have also shown diurnal changes in stream chemistry. The objectives of this study were to measure N O fluxes and dissolved N O concentrations from a spring-fed temperate river to determine if diurnal cycles were occurring. The study was performed during a 72 h period, over a 180 m reach, using headspace chamber methodology. Significant diurnal cycles were observed in radiation, river temperature and chemistry including dissolved N O-N concentrations. These data were used to further assess the IPCC methodology and experimental methodology used. River NO -N and N O-N concentrations averaged 3.0 mg L and 1.6 μg L , respectively, with N O saturation reaching a maximum of 664%. The N O-N fluxes, measured using chamber methodology, ranged from 52 to 140 μg m  h while fluxes predicted using the dissolved N O concentration ranged from 13 to 25 μg m  h . The headspace chamber methodology may have enhanced the measured N O flux and this is discussed. Diurnal cycles in N O% saturation were not large enough to influence downstream N transfer or N form with variability in measured N O fluxes greater and more significant than diurnal variability in N O% saturation. The measured N O fluxes, extrapolated over the study reach area, represented only 6 × 10 % of the NO -N that passed through the study reach over a 72 h period. This is only 0.1% of the IPCC calculated flux.