In situ N2O emissions are not mitigated by hippuric and benzoic acids under denitrifying conditions

This research was financially supported under the National Development Plan, through the Research Stimulus Fund, administered by the Department of Agriculture, Food and the Marine (Grant numbers RSF10/RD/SC/716 and 11S138).peer-reviewedRuminant urine patches deposited onto pasture are a significant source of greenhouse gas nitrous oxide (N2O) from livestock agriculture. Increasing food demand is predicted to lead to a rise in ruminant numbers globally, which, in turn will result in elevated levels of urine-derived N2O. Therefore mitigation strategies are urgently needed. Urine contains hippuric acid and together with one of its breakdown products, benzoic acid, has previously been linked to mitigating N2O emissions from urine patches in laboratory studies. However, the sole field study to date found no effect of hippuric and benzoic acid concentration on N2O emissions. Therefore the aim of this study was to investigate the in situ effect of these urine constituents on N2O emissions under conditions conducive to denitrification losses. Unadulterated bovine urine (0 mM of hippuric acid, U) was applied, as well as urine amended with either benzoic acid (96 mM, U + BA) or varying rates of hippuric acid (8 and 82 mM, U + HA1, U + HA2). Soil inorganic nitrogen (N) and N2O fluxes were monitored over a 66 day period. Urine application resulted in elevated N2O flux for 44 days. The largest N2O fluxes accounting for between 13% (U) and 26% (U + HA1) of total loss were observed on the day of urine application. Between 0.9 and 1.3% of urine-N was lost as N2O. Cumulative N2O loss from the control was 0.3 kg N2O–N ha− 1 compared with 11, 9, 12, and 10 kg N2O–N ha− 1 for the U, U + HA1, U + HA2, and U + BA treatments, respectively. Incremental increases in urine HA or increase in BA concentrations had no effect on N2O emissions. Although simulation of dietary manipulation to reduce N2O emissions through altering individual urine constituents appears to have no effect, there may be other manipulations such as reducing N content or inclusion of synthetic inhibitory products that warrant further investigation.Department of Agriculture, Food and the Marin

Improving and disaggregating N2O emission factors for ruminant excreta on temperate pasture soils

pre-printCattle excreta deposited on grazed grasslands are a major source of the greenhouse gas (GHG) nitrous oxide (N2O). Currently, many countries use the IPCC default emission factor (EF) of 2% to estimate excreta-derived N2O emissions. However, emissions can vary greatly depending on the type of excreta (dung or urine), soil type and timing of application. Therefore three experiments were conducted to quantify excreta-derived N2O emissions and their associated EFs, and to assess the effect of soil type, season of application and type of excreta on the magnitude of losses. Cattle dung, urine and artificial urine treatments were applied in spring, summer and autumn to three temperate grassland sites with varying soil and weather conditions. Nitrous oxide emissions were measured from the three experiments over 12 months to generate annual N2O emission factors. The EFs from urine treated soil was greater (0.30–4.81% for real urine and 0.13–3.82% for synthetic urine) when compared with dung (− 0.02–1.48%) treatments. Nitrous oxide emissions were driven by environmental conditions and could be predicted by rainfall and temperature before, and soil moisture deficit after application; highlighting the potential for a decision support tool to reduce N2O emissions by modifying grazing management based on these parameters. Emission factors varied seasonally with the highest EFs in autumn and were also dependent on soil type, with the lowest EFs observed from well-drained and the highest from imperfectly drained soil. The EFs averaged 0.31 and 1.18% for cattle dung and urine, respectively, both of which were considerably lower than the IPCC default value of 2%. These results support both lowering and disaggregating EFs by excreta type.This research was financially supported under the National Development Plan, through the Research Stimulus Fund, administered by the Department of Agriculture, Food and the Marine (Grant numbers RSF10/RD/SC/716 and 11S138)

The effect of precipitation and application rate on dicyandiamide persistence and efficiency in two Irish grassland soils

peer-reviewedThe nitrification inhibitor dicyandiamide (DCD) has had variable success in reducing nitrate (NO3-) leaching and nitrous oxide (N2O) emissions from soils receiving nitrogen (N) fertilisers. Factors such as soil type, temperature and moisture have been linked to the variable efficacy of DCD. Since DCD is water soluble it can be leached from the rooting zone where it is intended to inhibit nitrification. Intact soil columns (15 cm diameter by 35 cm long) were taken from luvic gleysol and haplic cambisol grassland sites and placed in growth chambers. DCD was applied at 15 or 30 kg DCD ha-1, with high or low precipitation. Leaching of DCD, mineral N and the residual soil DCD concentrations were determined over eight weeks High precipitation increased DCD in leachate and decreased recovery in soil. A soil x DCD rate interaction was detected for the DCD unaccounted (proxy for degraded DCD). In the cambisol degradation of DCD was high (circa 81%) and unaffected by DCD rate. In contrast DCD degradation in the gleysol was lower and differentially affected by rate, 67 and 46% for the 15 and 30 kg ha-1 treatments, respectively. Differences DCD degradation rates between soils may be related to differences in organic matter content and associated microbiological activity. Variable degradation rates of DCD in soil, unrelated to temperature or moisture, may contribute to varying DCD efficacy. Soil properties should be considered when tailoring DCD strategies for improving nitrogen use efficiency and crop yields, through the reduction of reactive nitrogen loss.This research was financially supported under the National Development Plan, through the Research Stimulus Fund, administered by the Department of Agriculture, Food and the Marine under grants 07519 and 07545

An evaluation of urine patch simulation methods for nitrous oxide emission measurement

peer-reviewedGlobal nitrous oxide (N2O) inventory estimates for pasture systems are refined based on measurements of N2O loss from simulated urine patches. A variety of methods are used for patch simulation but they frequently use a uniform wetted area (UWA), often smaller than a bovine urine patch. However, natural patches follow non-uniform infiltration patterns expanding naturally from a point of deposit with a non-wetted zone of influence. Using 2 litres of urine the UWA method was compared, using a 0·156 m2 collar, with a naturally expanding effective area (NEEA) method, using a 0·462 m2 collar under high (HL) and low (LL) N2O loss conditions. The method chosen affects urine nitrogen (N) loading to the soil. Under HL the UWA method induced a N2O-N loss of 280·6 mg/patch, significantly less than the 434·8 mg/patch loss for the NEEA method, for the same simulated urination. Under LL there was no method effect. Efforts should be made to employ patch simulation methods, which mimic natural deposits and can be achieved, at least in part, by: (a) Using a urine volume and N content similar to that of the animal of interest. (b) Allowing natural infiltration of the chosen urine volume to permit tapering towards the edges. (c) Measuring from the zone of influence in addition to the wetted area, i.e. the patch effective area

Impact of fertiliser nitrogen formulation, and N stabilisers on nitrous oxide emissions in spring barley

The application of nitrogen (N) fertilisers to agricultural soils is a major source of nitrous oxide (N2O) emissions. The Intergovernmental Panel on Climate Change (IPCC) has set a default emission factor of 1% (EF1) for N fertiliser applied to managed agricultural soils. This value does not differentiate between different N fertiliser formulations or rates of N application. The objective of this field study under spring barley was to determine N2O EF’s for different N fertiliser formulations including urea and urea stabilised with the nitrification inhibitor dicyandiamide (DCD) and/or the urease inhibitor N-(n-butyl) thiophosphoric triamide (NBPT) and to evaluate their N2O loss abatement potential relative to calcium ammonium nitrate (CAN). The highest EF1 measured was 0.49% for CAN which was less than half the IPCC default value of 1%. While the urease inhibitor did not reduce emissions relative to CAN; the nitrification inhibitor significantly reduced emissions compared to CAN with EF1 as low as 0.00% for a typical spring barley site. There was no significant impact of CAN or urea application rate on EF1 but there was a significant negative relationship observed for urea in 2013. The study highlights the importance of generating higher Tier emission factors in terms of fertiliser type for use in national inventories

A field-based comparison of ammonia emissions from six Irish soil types following urea fertiliser application

peer-reviewedAmmonia (NH3) emissions from a range of soil types have been found to differ under laboratory conditions. However, there is lack of studies comparing NH3 emissions from different soil types under field conditions. The objective was to compare NH3 emissions from six different soil types under similar environmental conditions in the field following urea fertiliser application. The study was conducted on a lysimeter unit and NH3 emissions were measured, using wind tunnels, from six different soil types with varying soil characteristics following urea fertiliser application (80 kg N/ha). On average, 17.6% (% total N applied) was volatilised, and there was no significant difference in NH3 emissions across all soil types. Soil variables, including pH, cation exchange capacity and volumetric moisture, were not able to account for the variation in emissions. Further field studies are required to improve the urea-NH3 emission factor used for Ireland’s NH3 inventory

Temperate Grassland Yields and Nitrogen Uptake Are Influenced by Fertilizer Nitrogen Source

This research was supported under the National Development Plan through the Research Stimulus Fund administered by the Department of Agriculture, Food and the Marine (Grants RSF10-/RD/SC/716 and RSF11S138) and from the Department of Agriculture and Rural Development for Northern Ireland and by the Teagasc Walsh Fellowship Scheme.peer reviewedIn temperate grasslands, N source influences greenhouse gas emissions. Nitrification and urea hydrolysis inhibitors can reduce these losses. The objective of this study was to evaluate the impact of N source, urease inhibitors, and nitrification inhibitors on temperate grassland yields and N uptake. Experiments were conducted at three locations over 2 years (6 site-years) on the island of Ireland, covering a range of soils and climatic conditions. Results showed that calcium ammonium nitrate (CAN), urea+N-(n-butyl) thiophosphoric triamide (NBPT), urea+NBPT+dicyandiamide (DCD), and urea had equal annual dry matter yield. Urea+DCD had lower dry matter yield than CAN for 3 site-years. Calcium ammonium nitrate and urea+NBPT consistently had the same N uptake, urea+DCD had lower N uptake than CAN in 4 of 6 site-years, urea had lower N uptake than CAN in 2 site-years, and urea+NBPT+DCD had lower N uptake than CAN in 1 site-year. Urea+NBPT is a cost-effective alternative to CAN, which is consistently equal in terms of yield and N uptake in temperate grassland.Teagasc Walsh Fellowship ProgrammeDepartment of Agriculture and Rural Development for Northern IrelandDepartment of Agriculture, Food and the Marin

Granular Impact: A Grain-scale Approach

This work summarizes a series of studies on two-dimensional granular impact, where an intruding object strikes a granular material at high speed. Many previous studies on granular impact have used a macroscopic force law, which is dominated by an inertial drag term proportional to the intruder velocity squared. The primary focus here is on the microscopic force response of the granular material, and how the grain-scale effects give rise to this inertial drag term. We show that the inertial drag arises from intermittent collisions with force-chain-like structures. We construct a simple collisional model to explain the inertial drag, as well as off-axis instability and rotations. Finally, we show how the granular response changes when the intruder speed approaches $d/t_c$, leading to a failure of the inertial drag description in this regime. Here, $d$ is the mean particle diameter and $t_c$ the characteristic momentum-transfer time between two grains.Comment: This is draft version of a book chapter appearing in "Rapid Penetration into Granular Media" (eds. Iskander et al.

The interactive effects of fertiliser nitrogen with dung and urine on nitrous oxide emissions in grassland

The authors wish to thank the Environmental Protection Agency for funding support under the Environmental Research Technological Development and Innovation programme and the Irish Department of Agriculture, Food and the Marine for funding support (Grant numbers RSF 13S430 and 11S138).peer-reviewedNitrous oxide (N2O) is an important and potent greenhouse gas (GHG). Although application of nitrogen (N) fertiliser is a feature of many grazing systems, limited data is available on N2O emissions in grassland as a result of the interaction between urine, dung and fertiliser N. A small plot study was conducted to identify the individual and interactive effects of calcium ammonium nitrate (CAN) fertiliser, dung and urine. Application of CAN with dung and urine significantly increased the mass of N2O-N emission. Importantly, the sum of N2O-N emitted from dung and CAN applied individually approximated the emission from dung and CAN fertiliser applied together, that is, an additive effect. However, in the case of urine and CAN applied together, the emission was more than double the sum of the emission from urine and CAN fertiliser applied individually, that is, a multiplicative effect. Nitrous oxide emissions from dung, urine and fertiliser N are typically derived individually and these individual emission estimates are aggregated to produce estimates of N2O emission. The presented findings have important implications for how individual emission factors are aggregated; they suggest that the multiplicative effect of the addition of CAN fertiliser to urine patches needs to be taken into account to refine the estimation of N2O emissions from grazing grasslands.The authors wish to thank the Environmental Protection Agency for funding support under the Environmental Research Technological Development and Innovation programme and the Irish Department of Agriculture, Food and the Marine for funding support (Grant numbers RSF 13S430 and 11S138)

A methodological framework to determine optimum durations for the construction of soil water characteristic curves using centrifugation

peer-reviewedDuring laboratory assessment of the soil water characteristic curve (SWCC), determining equilibrium at various pressures is challenging. This study establishes a methodological framework to identify appropriate experimental duration at each pressure step for the construction of SWCCs via centrifugation. Three common temporal approaches to equilibrium – 24-, 48- and 72-h – are examined, for a grassland and arable soil. The framework highlights the differences in equilibrium duration between the two soils. For both soils, the 24-h treatment significantly overestimated saturation. For the arable site, no significant difference was observed between the 48- and 72-h treatments. Hence, a 48-h treatment was sufficient to determine ‘effective equilibrium’. For the grassland site, the 48- and 72-h treatments differed significantly. This highlights that a more prolonged duration is necessary for some soils to conclusively determine that effective equilibrium has been reached. This framework can be applied to other soils to determine the optimum centrifuge durations for SWCC construction.Teagasc Walsh Fellowship Programm