Nitrogen fertiliser interactions with urine deposit affect nitrous oxide emissions from grazed grasslands

Cattle excreta deposited on grazed pastures are responsible for one fifth of the global anthropogenic nitrous oxide (N2O) emissions. One of the key nitrogen (N) sources is urine deposited from grazing animals, which contributes to very large N loadings within small areas. The main objective of this plot study was to establish whether the application of N fertiliser and urine deposit from dairy cows synergistically interacts and thereby increases N2O emissions, and how such interaction is influenced by the timing of application. The combined application of fertiliser (calcium ammonium nitrate) and urine significantly increased the cumulative N2O emissions as well as the N2O emission factor (EF) from 0.35 to 0.74 % in spring and from 0.26 to 0.52 % in summer. By contrast, EFs were lower when only fertiliser (0.31 % in spring, 0.07 % in summer) or urine was applied (0.33 % in spring, 0.28 % in summer). In autumn, N2O emissions were larger than in other seasons and the emissions from the combined application were not statistically different to those from either the separately applied urine or N fertiliser (EF ranging from 0.72 to 0.83, p-value < 0.05). The absence of significant synergistic effect could be explained by weather conditions, particularly rainfall during the three days prior to and after application in autumn. This study implies that the interactive effects of N fertilisation and urine deposit, as well as the timing of the application on N2O emission need to be taken into account in greenhouse gas emission inventories

Solutions to enteric methane abatement in Ireland

peer-reviewedThe efficiency of Ireland’s grass-based livestock systems can be attributed to high outputs, low production costs and a low carbon footprint relative to housed systems. Methane (CH4) is a potent greenhouse gas (GHG) of which enteric fermentation from livestock production is a key source, being directly responsible for 57% of Irish agricultural GHG emissions. There are a number of strategies including dietary manipulation and breeding initiatives that have shown promising results as potential mitigation solutions for ruminant livestock production. However, the majority of international research has predominantly been conducted on confined systems. Given the economic viability of Irish livestock systems, it is vital that any mitigation methods are assessed at pasture. Such research cannot be completed without access to suitable equipment for measuring CH4 emissions at grazing. This review documents the current knowledge capacity in Ireland (publications and projects) and includes an inventory of equipment currently available to conduct research. A number of strategic research avenues are identified herein that warrant further investigation including breeding initiatives and dietary manipulation. It was notable that enteric CH4 research seems to be lacking in Ireland as it constituted 14% of Irish agricultural GHG research publications from 2016 to 2021. A number of key infrastructural deficits were identified including respiration chambers (there are none currently operational in the Republic of Ireland) and an urgent need for more pasture-based GreenFeed™ systems. These deficits will need to be addressed to enable inventory refinement, research progression and the development of effective solutions to enteric CH4 abatement in Ireland

Nitrogen fertiliser interactions with urine deposit affect nitrous oxide emissions from grazed grasslands

peer-reviewedCattle excreta deposited on grazed pastures are responsible for one fifth of the global anthropogenic nitrous oxide (N2O) emissions. One of the key nitrogen (N) sources is urine deposited from grazing animals, which contributes to very large N loadings within small areas. The main objective of this plot study was to establish whether the application of N fertiliser and urine deposit from dairy cows synergistically interacts and thereby increases N2O emissions, and how such interaction is influenced by the timing of application. The combined application of fertiliser (calcium ammonium nitrate) and urine significantly increased the cumulative N2O emissions as well as the N2O emission factor (EF) from 0.35 to 0.74 % in spring and from 0.26 to 0.52 % in summer. By contrast, EFs were lower when only fertiliser (0.31 % in spring, 0.07 % in summer) or urine was applied (0.33 % in spring, 0.28 % in summer). In autumn, N2O emissions were larger than in other seasons and the emissions from the combined application were not statistically different to those from either the separately applied urine or N fertiliser (EF ranging from 0.72 to 0.83, p-value < 0.05). The absence of significant synergistic effect could be explained by weather conditions, particularly rainfall during the three days prior to and after application in autumn. This study implies that the interactive effects of N fertilisation and urine deposit, as well as the timing of the application on N2O emission need to be taken into account in greenhouse gas emission inventories.Teagas

Reducing nitrous oxide emissions by changing N fertiliser use from calcium ammonium nitrate (CAN) to urea based formulations

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 RSF11S138) and from the Department of Agriculture and Rural Development (Ref: DARD Evidence and Innovation project 13/04/06) for Northern Ireland. The first author gratefully acknowledges funding received from the Teagasc Walsh Fellowship Scheme (Ref: 2012005).peer-reviewedThe accelerating use of synthetic nitrogen (N) fertilisers, to meet the world's growing food demand, is the primary driver for increased atmospheric concentrations of nitrous oxide (N2O). The IPCC default emission factor (EF) for N2O from soils is 1% of the N applied, irrespective of its form. However, N2O emissions tend to be higher from nitrate-containing fertilisers e.g. calcium ammonium nitrate (CAN) compared to urea, particularly in regions, which have mild, wet climates and high organic matter soils. Urea can be an inefficient N source due to NH3 volatilisation, but nitrogen stabilisers (urease and nitrification inhibitors) can improve its efficacy. This study evaluated the impact of switching fertiliser formulation from calcium ammonium nitrate (CAN) to urea-based products, as a potential mitigation strategy to reduce N2O emissions at six temperate grassland sites on the island of Ireland. The surface applied formulations included CAN, urea and urea with the urease inhibitor N-(n-butyl) thiophosphoric triamide (NBPT) and/or the nitrification inhibitor dicyandiamide (DCD). Results showed that N2O emissions were significantly affected by fertiliser formulation, soil type and climatic conditions. The direct N2O emission factor (EF) from CAN averaged 1.49% overall sites, but was highly variable, ranging from 0.58% to 3.81. Amending urea with NBPT, to reduce ammonia volatilisation, resulted in an average EF of 0.40% (ranging from 0.21 to 0.69%)-compared to an average EF of 0.25% for urea (ranging from 0.1 to 0.49%), with both fertilisers significantly lower and less variable than CAN. Cumulative N2O emissions from urea amended with both NBPT and DCD were not significantly different from background levels. Switching from CAN to stabilised urea formulations was found to be an effective strategy to reduce N2O emissions, particularly in wet, temperate grassland.Department of Agriculture and Rural Development for Northern IrelandTeagasc Walsh Fellowship ProgrammeDepartment of Agriculture, Food and the Marin

Assessing the impact of long-term soil phosphorus on N-transformation pathways using 15N tracing

peer-reviewedA laboratory incubation study was conducted on a temperate grassland soil to quantify the main mineral nitrogen (N) transformation rates and pathways via a15N tracing approach. Soil samples were taken from a long-term phosphorus (P) trial to investigate the effects on gross N-transformations under high and low phosphorus amendment. The soils were incubated over a 2-week period and treated with ammonium-nitrate (NH4NO3) which was applied to the soil both with and without a glucose amendment and labelled with 15N either on the ammonium (NH4+) or nitrate (NO3−) moiety at 50% atom enrichment. The results showed immobilisation to greatly outweigh mineralisation and that NO3− was predominantly produced via heterotrophic nitrification. Individual pathways for NO3− production were quantified including oxidation of NH4+, recalcitrant and labile organic N. Oxidation of labile organic N to NO3−, a newly considered pathway, accounted for between 63 and 83% of total NO3− production across the various treatments and P levels. This process was significantly higher in the low-P rather than the high-P soils (p < 0.05), highlighting the effect of soil P on the microbial community.National Development Pla

Assessing nitrous oxide emissions in time and space with minimal uncertainty using static chambers and eddy covariance from a temperate grassland

Where nitrogen input from fertilizer application exceeds plant demands, hotspots of microbially produced nitrous oxide (N2O) can exhibit disproportionately high rates of emissions relative to longer periods of time, known as hot moments. Hotspots and hot moments of N2O are sensitive to changes in agricultural management and weather, making it difficult to accurately quantify N2O emissions. This study investigates the spatial and temporal variability of N2O emissions using both static chambers (CH) and eddy covariance (EC) techniques, measured at a grassland site subject to four fertilizer applications of calcium ammonium nitrate (CAN) in 2019. Daily mean CH emissions were calculated using the arithmetic method and Bayesian statistics to explicitly account for the log-normal distribution of the dataset. N2O fluxes measured by CH and EC were most comparable when flux measurements were > 115 N2O-N µg m − 2 hr −1, and EC and CH measurements showed spatial and temporal alignment when CH n ≥ 15. Where n ≤ 5, the Bayesian method produced large uncertainties due to the difficulty of fitting an arithmetic mean from a log-normally distributed data set with few flux measurements. Annual EC fluxes, gap-filled using a multi-variate linear model, showed a strong correlation with measured flux values (R 2 = 0.92). Annual cumulative fluxes by EC were higher (3.35 [± 0.5] kg N ha−1) than CH using the arithmetic (2.98 [± 0.17] kg N ha−1) and Bayesian method (3.13 [± 0.24] kg N ha−1), which quantified emission factors of 1.46%, 1.30% and 1.36%, respectively. This study implies that a large sample size and frequent CH flux measurements are necessary for comparison with EC fluxes and that Bayesian statistics are an appropriate method for estimating realistic means and ranges of uncertainty for CH flux data sets

Does soil biology hold the key to optimized slurry management? A manifesto for research

The application of agricultural biosolids to land is likely to increase on farms as pressures intensify to manage nutrients and carbon, especially with regard to slurry. Although much work has been carried out in this area, it has tended to focus on specific aspects of the application-use cycle, without a coherent framework and notably the role of soil biology has been little studied in this context, or considered appropriately in the development and application of slurry management systems. In this review article we present a hypothesis that the configuration of the soil microbial community is determined by the history of long-term inputs to which the community has been subjected and that the resultant configuration determines the instantaneous responses of the associated soil to the presence of slurries, and posit a set of critical questions which would effectively test this.</p