• Land Drainage - A farmer’s practical guide to draining grassland in Ireland

      Tuohy, Patrick; Fenton, Owen; O'Loughlin, James; Humphreys, James (Teagasc, 30/07/2013)
      No drainage work should be carried out before the drainage characteristics of the soil are established by a site and soil test pit investigation. • Two types of drainage system exist: a groundwater drainage system and a shallow drainage system. The design of the system depends entirely on the drainage characteristics of the soil. • Distinguishing between the two types of drainage systems essentially comes down to whether or not a permeable layer is present (at a workable depth) that will allow the flow of water with relative ease. If such a layer is evident, a piped drain system at that depth is likely to be effective. If no such layer is found during soil test pit investigations, it will be necessary to improve the drainage capacity of the soil. This involves a disruption technique such as moling, gravel moling or subsoiling in tandem with collector drains. • Drains are not effective unless they are placed in a free draining soil layer or complimentary measures (mole drainage, subsoiling) are used to improve soil drainage capacity. If water is not moving through the soil in one or other of these two ways, the water table will not be lowered. • Outfall level must not dictate the drainage system depth. If a free draining layer is present, it must be utilised. • Drain pipes should always be used for drains longer than 30 m. If these get blocked it is a drainage stone and not a drainage pipe issue. • Drainage stone should not be filled to the top of the field trench except for very limited conditions (the bottom of an obvious hollow). Otherwise it is an extremely expensive way of collecting little water. • Most of the stone being used for land drainage today is too big. Clean aggregate in the 10–40 mm (0.4 to 1.5 inch approx) grading band should be used. Generally you get what you pay for. • Subsoiling is not effective unless a shallow impermeable layer is being broken or field drains have been installed prior to the operation. Otherwise it will not have any long-term effect and may do more harm than good. • Most land drainage systems are poorly maintained. Open drains should be clean and as deep as possible and field drains feeding into them should be regularly rodded or jetted.
    • Linking Hydro-Geophysics and Remote Sensing Technology for Sustainable Water and Agricultural Catchment Management

      O'Leary, Dave; Fenton, Owen; Mellander, Per-Erik; Tuohy, Patrick; Brown, C.; Daly, E. (2019-05)
      The acquisition of sub-surface data for agricultural purposes is traditionally achieved by in situ point sampling in the top 2m over limited target areas (farm scale ~ km2) and time periods. This approach is inadequate for integrated regional (water catchment ~ 100 km2) scale management strategies which require an understanding of processes varying over decadal time scales in the transition zone (~ 10’s m) from surface to bedrock. With global food demand expected to increase by 100% by 2050, there are worldwide concerns that achievement of production targets will be at the expense of water quality. In order to overcome the limitations of the traditional approach, this research programme will combine airborne and ground geophysics with remote sensing technologies to access hydrogeological and soil structure information on Irish Soils at multiple spatial scales. It will address this problem in the context of providing tools for the sustainable management of agricultural intensification envisioned in Food Harvest 2020 and Food Wise 2025 and considering the EU Habitats and Water Framework Directives (WFD), Clean Air Policy and Soil Thematic Strategies. The work will use existing ground based geophysical and hydrogeological data from Teagasc Agricultural Catchment Programme (ACP) and Heavy Soil sites co-located ground and airborne electromagnetic data. Neural Networks training and Machine learning approaches will supplement traditional geophysical workflows. Work will then focus on upscaling results from ACP to WFD catchment scale. This upscaling will require modification of traditional satellite remote sensing conceptual frameworks to analyse heterogeneous, multi-temporal data streams.
    • Linking hydrogeochemistry to nitrate abundance in groundwater in agricultural settings in Ireland

      Jahangir, Mohammad M. R.; Johnston, Paul; Khalil, Mohammed I.; Richards, Karl G.; Department of Agriculture, Food and the Marine, Ireland; Department of Civil, Structural and Environmental Engineering, Trinity College Dublin; RSF 06383 (Elsevier, 11/05/2012)
      Nitrate (NO3-–N) contamination of groundwater and associated surface waters is an increasingly important global issue with multiple impacts on terrestrial, aquatic and atmospheric environments. Investigation of the distribution of hydrogeochemical variables and their connection with the occurrence of NO3-–N provides better insights into the prediction of the environmental risk associated with nitrogen use within agricultural systems. The research objective was to evaluate the effect of hydrogeological setting on agriculturally derived groundwater NO3-–N occurrence. Piezometers (n = 36) were installed at three depths across four contrasting agricultural research sites. Groundwater was sampled monthly for chemistry and dissolved gases, between February 2009 and January 2011. Mean groundwater NO3-–N ranged 0.7–14.6 mg L−1, with site and groundwater depth being statistically significant (p < 0.001). Unsaturated zone thickness and saturated hydraulic conductivity (Ksat) were significantly correlated with dissolved oxygen (DO) and redox potential (Eh) across sites. Groundwater NO3-–N occurrence was significantly negatively related to DOC and methane and positively related with Eh and Ksat. Reduction of NO3-–N started at Eh potentials <150 mV while significant nitrate reduction occurred <100 mV. Indications of heterotrophic and autotrophic denitrification were observed through elevated dissolved organic carbon (DOC) and oxidation of metal bound sulphur, as indicated by sulphate (SO42-). Land application of waste water created denitrification hot spots due to high DOC losses. Hydrogeological settings significantly influenced groundwater nitrate occurrence and suggested denitrification as the main control.
    • Long-Term Persistence and Leaching of Escherichia coli in Temperate Maritime Soils

      Brennan, Fiona P.; O'Flaherty, Vincent; Kramers, Gaelene; Grant, Jim; Richards, Karl G.; Irish Research Council for Science, Engineering and Technology (American Society for Microbiology, 2009-12)
      Enteropathogen contamination of groundwater, including potable water sources, is a global concern. The spreading on land of animal slurries and manures, which can contain a broad range of pathogenic microorganisms, is considered a major contributor to this contamination. Some of the pathogenic microorganisms applied to soil have been observed to leach through the soil into groundwater, which poses a risk to public health. There is a critical need, therefore, for characterization of pathogen movement through the vadose zone for assessment of the risk to groundwater quality due to agricultural activities. A lysimeter experiment was performed to investigate the effect of soil type and condition on the fate and transport of potential bacterial pathogens, using Escherichia coli as a marker, in four Irish soils (n 9). Cattle slurry (34 tonnes per ha) was spread on intact soil monoliths (depth, 1 m; diameter, 0.6 m) in the spring and summer. No effect of treatment or the initial soil moisture on the E. coli that leached from the soil was observed. Leaching of E. coli was observed predominantly from one soil type (average, 1.11 0.77 CFU ml 1), a poorly drained Luvic Stagnosol, under natural rainfall conditions, and preferential flow was an important transport mechanism. E. coli was found to have persisted in control soils for more than 9 years, indicating that autochthonous E. coli populations are capable of becoming naturalized in the low-temperature environments of temperate maritime soils and that they can move through soil. This may compromise the use of E. coli as an indicator of fecal pollution of waters in these regions.
    • Lough Melvin: Developing cost-effective measures to prevent phosphorus enrichment of a unique aquatic habitat

      Schulte, Rogier P.; Doody, Donnacha G.; Byrne, Paul; Cockerill, C.; Carton, Owen T.; Lough Melvin Nutrient Reduction Programme (School of Agriculture, Food Science and Veterinary Medicine, University College Dublin in association with Teagasc, 2009)
      Lough Melvin, located on the border of Leitrim (Republic of Ireland) and Fermanagh (Northern Ireland), is unique among Irish lakes, supporting a fish community typical of a natural post-glacial salmonid lake, and has been designated as a Special Area of Conservation (SAC). The biodiversity of the lake is vulnerable to changes in water quality resulting from eutrophication, and over the last 15 years, phosphorus (P) concentrations have increased to the upper range of mesotrophic classification. Agriculture has been reported as one of the main contributors of P loadings to the lake, which poses an apparent paradox in light of the low-intensity nature of farming practices in the catchment. The objectives of the project reported on here were to identify the dominant P pressure and pathway risks governing P loss in the catchment, and to evaluate and select potential mitigation measures, based on an assessment of cost-effectiveness and farmer preference. Throughout this project, we employed an explicitly participatory approach, with farmer stakeholders inputting directly into the identification and evaluation of mitigation measures. We identified risks on 50 survey farms by using the modified P Ranking Scheme. A suite of 25 potential mitigation strategies was identified from the literature and on-farm interviews. For each measure, we derived the order of magnitude of potential costs, impact, and cost-effectiveness, and measures were preferentially ranked by 25 participating farmers. The resulting ranking of measures showed that support for nutrient management planning and soil analysis was the most cost-effective and popular measure aimed at reducing P pressures in the long term, while installation of sediment traps in drainage ditches was the most cost-effective and popular measure aimed at reducing P transport vectors in the short term. We demonstrate that through this careful evaluation and selection of mitigation measures, over 50% of potential total reduction in P loss can be achieved at c. 5% of potential total cost. In addition, we show that measures commonly proposed to mitigate against “high-visibility risks” are not necessarily cost-effective or acceptable to farmer stakeholders. The results of this study are specific to the biophysical environment and farming context of the Lough Melvin catchment, however, we suggest that the approach taken in our project may be used as a template for the formulation of regional catchment management plans, such as the draft river basin district management plans required under the Water Framework Directive.
    • Management, regulation and environmental impacts of nitrogen fertilization in northwestern Europe under the Nitrates Directive; a benchmark study

      van Grinsven, H. J. M.; ten Berge, H. F. M.; Dalgaard, T.; Fraters, B.; Durand, P.; Hart, A.; Hofman, G.; Jacobsen, B.H.; Lalor, Stanley T. J.; Lesschen, Jan Peter; et al. (European Geosciences Union, 14/12/2012)
      Implementation of the Nitrates Directive (NiD) and its environmental impacts were compared for member states in the northwest of the European Union (Ireland, United Kingdom, Denmark, the Netherlands, Belgium, Northern France and Germany). The main sources of data were national reports for the third reporting period for the NiD (2004–2007) and results of the MITERRA-EUROPE model. Implementation of the NiD in the considered member states is fairly comparable regarding restrictions for where and when to apply fertilizer and manure, but very different regarding application limits for N fertilization. Issues of concern and improvement of the implementation of the NiD are accounting for the fertilizer value of nitrogen in manure, and relating application limits for total nitrogen (N) to potential crop yield and N removal. The most significant environmental effect of the implementation of the NiD since 1995 is a major contribution to the decrease of the soil N balance (N surplus), particularly in Belgium, Denmark, Ireland, the Netherlands and the United Kingdom. This decrease is accompanied by a modest decrease of nitrate concentrations since 2000 in fresh surface waters in most countries. This decrease is less prominent for groundwater in view of delayed response of nitrate in deep aquifers. In spite of improved fertilization practices, the southeast of the Netherlands, the Flemish Region and Brittany remain to be regions of major concern in view of a combination of a high nitrogen surplus, high leaching fractions to groundwater and tenacious exceedance of the water quality standards. On average the gross N balance in 2008 for the seven member states in EUROSTAT and in national reports was about 20 kg N ha−1 yr−1 lower than by MITERRA. The major cause is higher estimates of N removal in national reports which can amount to more than 50 kg N ha−1 yr−1. Differences between procedures in member states to assess nitrogen balances and water quality and a lack of cross-boundary policy evaluations are handicaps when benchmarking the effectiveness of the NiD. This provides a challenge for the European Commission and its member states, as the NiD remains an important piece of legislation for protecting drinking water quality in regions with many private or small public production facilities and controlling aquatic eutrophication from agricultural sources.
    • Mapping Soils in Ireland

      Simo, Iolanda; Constanje, R.; Fealy, Reamonn; Hallett, S.; Hannam, Jacqueline; Holden, Nicholas M.; Jahns, G.; Jones, B.; Massey, P.; Mayr, T.; et al. (CRC Press, 2014)
      Harmonised soil data across Europe with a 1:250 000 geo-referenced soil database will allow for exchange of data across member states and the provide the information needed for reporting on issues re-lating to soil quality under a future Soil Framework Directive. The current status of soils data available in Eu-rope is inconsistent at best. The Irish Soil Information System (ISIS) project is currently developing a national soil map of 1:250,000 and an associated digital soil information system, providing both spatial and quantita-tive information on soil types and properties across Ireland. Both the map and the information system will be freely available to the public through a designated website.
    • Mapping the broad habitats of the Burren using satellite imagery

      Parr, Sharon; O'Donovan, Grace; Finn, John (Teagasc, 01/03/2006)
      This project has successfully used satellite imagery to survey and map the extent and spatial distribution of broad habitat types within the Burren, and we have represented this information on a digitised habitat map. this information on a digitised habitat map. This map is the first to show the distribution of the broad habitats of the Burren and will be an important tool in aiding future decisions as to how the habitats of the Burren should be managed to the benefit of both the farmer and the environment. The map provides the first estimate of the area of the Burren affected by scrub encroachment – this being one of the most significant threats to the EU priority habitats in the region. On a particularly challenging area with a high diversity and complexity of habitats, remote sensing appears to offer a very effective and cost-efficient alternative to broad-scale habitat mapping on a field-by-field basis. The use of high-resolution imagery and ground-truthing should be adopted to complete a detailed national survey of habitats and land use in Ireland. This would support more effective implementation of both the Agriculture sector’s obligations under the Habitats Directive, and agri-environmental schemes with wildlife objectives. The outputs provided by such mapping approaches could inform the targeting of agri-environmental objectives, and increase the efficiency of detecting areas of high conservation value for monitoring by more conventional methods. The detailed land use descriptions offered by such imagery are also of high relevance to modelling approaches and risk assessment for implementation of land use policies such as the Water Framework Directive and Nitrates Directive.
    • Measured and Simulated Nitrous Oxide Emissions from Ryegrass- and Ryegrass/White Clover-Based Grasslands in a Moist Temperate Climate

      Li, Dejun; Lanigan, Gary; Humphreys, James; Department of Agriculture, Food and the Marine, Ireland; RSF 07 516; RSF 07 511 (PLoS, 10/10/2011)
      There is uncertainty about the potential reduction of soil nitrous oxide (N2O) emission when fertilizer nitrogen (FN) is partially or completely replaced by biological N fixation (BNF) in temperate grassland. The objectives of this study were to 1) investigate the changes in N2O emissions when BNF is used to replace FN in permanent grassland, and 2) evaluate the applicability of the process-based model DNDC to simulate N2O emissions from Irish grasslands. Three grazing treatments were: (i) ryegrass (Lolium perenne) grasslands receiving 226 kg FN ha−1 yr−1 (GG+FN), (ii) ryegrass/white clover (Trifolium repens) grasslands receiving 58 kg FN ha−1 yr−1 (GWC+FN) applied in spring, and (iii) ryegrass/white clover grasslands receiving no FN (GWC-FN). Two background treatments, un-grazed swards with ryegrass only (G–B) or ryegrass/white clover (WC–B), did not receive slurry or FN and the herbage was harvested by mowing. There was no significant difference in annual N2O emissions between G–B (2.38±0.12 kg N ha−1 yr−1 (mean±SE)) and WC-B (2.45±0.85 kg N ha−1 yr−1), indicating that N2O emission due to BNF itself and clover residual decomposition from permanent ryegrass/clover grassland was negligible. N2O emissions were 7.82±1.67, 6.35±1.14 and 6.54±1.70 kg N ha−1 yr−1, respectively, from GG+FN, GWC+FN and GWC-FN. N2O fluxes simulated by DNDC agreed well with the measured values with significant correlation between simulated and measured daily fluxes for the three grazing treatments, but the simulation did not agree very well for the background treatments. DNDC overestimated annual emission by 61% for GG+FN, and underestimated by 45% for GWC-FN, but simulated very well for GWC+FN. Both the measured and simulated results supported that there was a clear reduction of N2O emissions when FN was replaced by BNF.
    • A methodological framework to determine optimum durations for the construction of soil water characteristic curves using centrifugation

      Vero, Sara E.; Healy, Mark G.; Henry, Tiernan; Creamer, Rachel E.; Ibrahim, Tristan G.; Forrestal, Patrick J.; Richards, Karl G.; Fenton, Owen; Teagasc Walsh Fellowship Programme (Teagasc (Agriculture and Food Development Authority), Ireland, 30/12/2016)
      During 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.
    • Methodological tests of the use of trace elements as tracers to assess root activity

      Hoekstra, Nyncke J.; Finn, John; Buchmann, Nina; Gockele, A.; Landert, L.; Prill, N.; Scherer-Lorenzen, M.; Luscher, L.; European Union; Irish Research Council; et al. (Springer, 2014-03)
      Background and aims There is increasing interest in how resource utilisation in grassland ecosystems is affected by changes in plant diversity and abiotic conditions. Research to date has mainly focussed on aboveground responses and there is limited insight into belowground processes. The aim of this study was to test a number of assumptions for the valid use of the trace elements caesium, lithium, rubidium and strontium as tracers to assess the root activity of several grassland species. Methods We carried out a series of experiments addressing the reliability of soil labelling, injection density, incubation time, application rate and the comparability of different tracers in a multiple tracer method. Results The results indicate that it is possible to achieve a reliable labelling of soil depths. Tracer injection density affected the variability but not the mean level of plant tracer concentrations. Tracer application rates should be based on pilot studies, because of site- and species-specific responses. The trace elements did not meet prerequisites to be used in a multiple tracer method. Conclusions The use of trace elements as tracers is potentially a very useful tool to give insight into plant root activity at different soil depths. This work highlights some of the main benefits and pitfalls of the method and provides specific recommendations to assist the design of tracer experiments and interpretation of the results.
    • Methodology for environmental assessment of agri-environment schemes: the Agri Environmental Footprint Index

      Finn, John; Louwagie, G.; Northey, G.; Purvis, Gordon; Balazs, K.; Mortimer, S.R.; Primdahl, J.; Vesterager, J.-P.; AE-Footprint project (Teagasc, 01/11/2010)
      Agri-environment schemes pay farmers for the provision of environmental services. Such schemes tend to have multiple measures that deliver multiple environmental objectives, and there is a lack of consistent methodology with which to measure the environmental benefits of such schemes. Funded by EU FP6, the Agri-Environment Footprint project (www.footprint.rdg.ac.uk) aimed to address this challenge, and this report provides results from selected components of the project.
    • Methodology for the location of a subsurface permeable reactive barrier for the remediation of point source pollution on an Irish farm

      Fenton, Owen; Healy, Mark G.; Richards, Karl G. (School of Agriculture, Food Science and Veterinary Medicine, University College Dublin in association with Teagasc, 2008)
      Nutrient loss from agricultural sources to water continues to be a national challenge. Diffuse pollution from agricultural sources is considered to be the primary cause of slight-to-moderate water pollution in Ireland, but agricultural point sources, such as farmyards, are often not considered due to their scattered spatial distribution and small areal extent. Agricultural point sources tend to be small and localised hot spots of nutrients and, therefore, can be efficiently treated using environmental technologies developed for wastewater and contaminated land treatment. A small area associated with soiled water irrigation, on a 4.27 ha case study site at Teagasc, Johnstown Environmental Research Centre, Ireland, was identified, where groundwater nitrate-nitrogen (NO3-N) concentration exceeds the maximum admissible drinking water concentration of 11.3 mg N L-1. A continuous, shallow permeable reactive barrier may be suitable to remediate point source pollution at this site. A methodology, based on site and groundwater characterisation, successfully located a site for a permeable reactive barrier.
    • Mid-infrared spectroscopy as an alternative to laboratory extraction for the determination of lime requirement in tillage soils

      Metzger, Konrad; Zhang, Chaosheng; Ward, Mark; Daly, Karen; Teagasc Walsh Fellowship Programme; Department for Agriculture Food and the Marine; RMIS 6837; 15/ICTAGRI 2 (Elsevier BV, 2020-04)
      Lime is a crucial soil conditioner to bring agricultural soils to optimum pH values for nutrient availability. Lime recommendations are typically determined in laboratory extractions, the most common being the “Shoemaker- McLean and Pratt” (SMP) buffer method, that requires carcinogenic reagents soon to be abolished under the EU legislation. As an alternative to wet chemistry, mid-infrared (MIR) spectroscopy has shown to be a cost-and time effective method at predicting soil properties. The capability and feasibility of diffuse reflectance infrared spectroscopy (DRIFTS) to predict lime requirement (LR) in tillage fields is examined. Samples from 41 cereal tillage fields (n = 655) are used to build a calibration for DRIFTS using partial least squares regression (PLSR). The samples were split into calibration set (31 fields, n=495) and validation set (10 fields, n= 160). After preprocessing with trim, smoothing and standard normal variate, a calibration model using 6 latent variables, provided R2 of 0.89 and root mean square error of cross-validation (RMSECV) of 1.56 t/ha. Prediction of all fields from the validation set resulted in R2 of 0.76 and root mean square error of prediction (RMSEP) of 1.68 t/ ha. The predictions of the single fields ranged from R2 values of 0.41 to 0.72, RMSEP of 0.48 to 4.2 t/ha and ratios of performance to inter-quartile distance (RPIQ) of 0.45 to 3.56. It was shown that the signals of soil constituents having an influence on the LR were picked up in the spectra and were identified in the loading weights of the PLSR. While the error is too high to predict the variability of LR within the field, MIR prediction using field averages provided a viable alternative to current laboratory methods for blanket spreading of lime on tillage fields.
    • Mobilisation or dilution? Nitrate response of karst springs to high rainfall events

      Huebsch, Manuela; Fenton, Owen; Horan, Brendan; Hennessy, Deirdre; Richards, Karl G.; Jordan, Philip; Goldscheider, N.; Butscher, C.; Blum, P.; Teagasc Walsh Fellowship Programme (European Geosciences Union, 05/11/2014)
      Nitrate (NO3−) contamination of groundwater associated with agronomic activity is of major concern in many countries. Where agriculture, thin free draining soils and karst aquifers coincide, groundwater is highly vulnerable to nitrate contamination. As residence times and denitrification potential in such systems are typically low, nitrate can discharge to surface waters unabated. However, such systems also react quickest to agricultural management changes that aim to improve water quality. In response to storm events, nitrate concentrations can alter significantly, i.e. rapidly decreasing or increasing concentrations. The current study examines the response of a specific karst spring situated on a grassland farm in South Ireland to rainfall events utilising high-resolution nitrate and discharge data together with on-farm borehole groundwater fluctuation data. Specifically, the objectives of the study are to formulate a scientific hypothesis of possible scenarios relating to nitrate responses during storm events, and to verify this hypothesis using additional case studies from the literature. This elucidates the controlling key factors that lead to mobilisation and/or dilution of nitrate concentrations during storm events. These were land use, hydrological condition and karstification, which in combination can lead to differential responses of mobilised and/or diluted nitrate concentrations. Furthermore, the results indicate that nitrate response in karst is strongly dependent on nutrient source, whether mobilisation and/or dilution occur and on the pathway taken. This will have consequences for the delivery of nitrate to a surface water receptor. The current study improves our understanding of nitrate responses in karst systems and therefore can guide environmental modellers, policy makers and drinking water managers with respect to the regulations of the European Union (EU) Water Framework Directive (WFD). In future, more research should focus on the high-resolution monitoring of karst aquifers to capture the high variability of hydrochemical processes, which occur at time intervals of hours to days.
    • Modelling Phosphorus for Grassland: Agronomically and Environmentally Sustainable Advice

      Schulte, Rogier P. (Teagasc, 01/01/2006)
      In 2006, the Nitrates Directive (through S.I. 378 (Anon, 2006)) was implemented in Ireland, aimed at reducing nutrient losses from agriculture to water bodies, i.e. surface waters, groundwater and estuarine waters. This legislation introduced strict regulation of nutrient management on Irish farms. Thus far, nutrient management had largely been based on Teagasc advice (Coulter, 2004). However, in the new policy climate, in addition to advice, compliance with legal limits is also required. This significant change in the practicalities surrounding nutrient management led to a review of Teagasc nutrient (phosphorus and nitrogen) advice, based on the following considerations: Traditionally, nutrient advice had largely been based on fertiliser rates for economically optimal productivity, i.e. rates at which further fertiliser applications would not result in higher economic returns. Now, SI 378 of 2006 demands that nutrient application rates do not exceed crop (grass) demand, nor result in nutrient losses that may have a negative impact on water quality. Previous phosphorus (P) advice (Coulter, 2004) was similar for all soil types, and did not account for potentially different P-requirements, or indeed potentially different risks of P-loss to water between soils. Previous P advice was based on returning optimum crop yields. However, grassland management in Ireland is increasingly focussed on maximising the amount of herbage grazed in situ. With extended grazing seasons and an increasing share of the animal diet consisting of grazed herbage, the scope and flexibility of diet supplementation through straights and concentrates is reduced. An increasing proportion of dietary P must be obtained from this grazed herbage as a result. Therefore P fertiliser strategies should no longer be based on yield responses alone, but in addition sustain adequate herbage P-concentrations in order to ensure that the dietary P requirements can be met on a non-supplemented diet of grazed herbage. Against this background, Teagasc, Johnstown Castle Environment Research Centre, undertook a major research programme, reviewing both agronomic and environmental aspects of P-advice for grassland.
    • Modelling soil bulk density at the landscape scale and its contributions to C stock uncertainty

      Taalab, K.P.; Corstanje, R.; Creamer, Rachel E.; Whelan, M. J.; Environmental Protection Agency (European Geosciences Union, 12/07/2013)
      Soil bulk density (Db) is a major contributor to uncertainties in landscape-scale carbon and nutrient stock estimation. However, it is time consuming to measure and is, therefore, frequently predicted using surrogate variables, such as soil texture. Using this approach is of limited value for estimating landscape-scale inventories, as its accuracy beyond the sampling point at which texture is measured becomes highly uncertain. In this paper, we explore the ability of soil landscape models to predict soil Db using a suite of landscape attributes and derivatives for both topsoil and subsoil. The models were constructed using random forests and artificial neural networks. Using these statistical methods, we have produced a spatially distributed prediction of Db on a 100 m × 100 m grid, which was shown to significantly improve topsoil carbon stock estimation. In comparison to using mean values from point measurements, stratified by soil class, we found that the gridded method predicted Db more accurately, especially for higher and lower values within the range. Within our study area of the Midlands, UK, we found that the gridded prediction of Db produced a stock inventory of over 1 million tonnes of carbon greater than the stratified mean method. Furthermore, the 95% confidence interval associated with total C stock prediction was almost halved by using the gridded method. The gridded approach was particularly useful in improving organic carbon (OC) stock estimation for fine-scale landscape units at which many landscape–atmosphere interaction models operate.
    • Multiple factors control the environmental effectiveness of agri-environment schemes: implications for design and evaluation

      Finn, John; Kurz, Isabelle; Bourke, David; European Union; European Commission; SSPE-CT-2003-502070 (School of Agriculture, Food Science and Veterinary Medicine, University College Dublin in association with Teagasc, 2008)
      Achieving and evaluating the environmental effectiveness of agri-environment schemes (AESs) has proven difficult. The design and ex ante evaluation of AESs is a crucial phase for ensuring effectiveness, but seems to receive relatively little attention. We propose a programme theory (a structured description of the various cause-and-effect relationships that underpin and achieve a policy initiative) for AESs that considers multiple factors that drive environmental performance at farm-scale (appropriate farm-level objectives, farmer compliance, implementation by institutions, and cause-and-effect relationship between management prescriptions and environmental objectives), and factors that determine how farm-scale performance aggregates to produce scheme-scale performance (participation rate, targeting, and threshold effects). These factors can be used as assessment criteria with which to pinpoint specific causes of AES failure, and thereby offer a practical approach to complement the design and evaluation of the environmental effects of AESs.
    • Mustard catch crop enhances denitrification in shallow groundwater beneath a spring barley field

      Jahangir, Mohammad M. R.; Minet, E.; Johnston, Paul; Premrov, Alina; Coxon, Catherine E.; Hackett, Richard; Richards, Karl G.; Department of Agriculture, Food and the Marine, Ireland; RSF 06383 (Elsevier, 26/12/2013)
      Over-winter green cover crops have been reported to increase dissolved organic carbon (DOC) concentrations in groundwater, which can be used as an energy source for denitrifiers. This study investigates the impact of a mustard catch crop on in situ denitrification and nitrous oxide (N2O) emissions from an aquifer overlain by arable land. Denitrification rates and N2O-N/(N2O-N + N2-N) mole fractions were measured in situ with a push–pull method in shallow groundwater under a spring barley system in experimental plots with and without a mustard cover crop. The results suggest that a mustard cover crop could substantially enhance reduction of groundwater nitrate NO3--N via denitrification without significantly increasing N2O emissions. Mean total denitrification (TDN) rates below mustard cover crop and no cover crop were 7.61 and 0.002 μg kg−1 d−1, respectively. Estimated N2O-N/(N2O-N + N2-N) ratios, being 0.001 and 1.0 below mustard cover crop and no cover crop respectively, indicate that denitrification below mustard cover crop reduces N2O to N2, unlike the plot with no cover crop. The observed enhanced denitrification under the mustard cover crop may result from the higher groundwater DOC under mustard cover crop (1.53 mg L−1) than no cover crop (0.90 mg L−1) being added by the root exudates and root masses of mustard. This study gives insights into the missing piece in agricultural nitrogen (N) balance and groundwater derived N2O emissions under arable land and thus helps minimise the uncertainty in agricultural N and N2O-N balances.
    • N leaching to groundwater from dairy production involving grazing over the winter on a clay-loam soil

      Necpalova, Magdalena; Fenton, Owen; Casey, Imelda A.; Humphreys, James; Department of Agriculture, Food and the Marine, Ireland; RSF07-511 (Elsevier B. V., 15/08/2012)
      This study investigated concentrations of various N species in shallow groundwater (< 2.2 m below ground level) and N losses from dairy production involving grazing over the winter period on a clay loam soil with a high natural attenuation capacity in southern Ireland (52˚51’N, 08˚21’W) over a two year period. A dense network of shallow groundwater piezometers was installed to determine groundwater flow direction and N spatial and temporal variation. Estimated vertical travel times through the unsaturated zone (<0.5 yr, time lag) allowed the correlation of management with groundwater N within a short space of time. There was a two way interaction of the system and sampling date (P < 0.05) on concentrations of DON, oxidised N and NO3--N. In contrast, concentrations of NH4+-N and NO2--N were unaffected by the dairy system. Grazing over the winter had no effect on N losses to groundwater. Mean concentrations of DON, NH4+-N, NO2--N and NO3--N were 2.16, 0.35, 0.01 and 0.37 mg L-1 respectively. Soil attenuation processes such as denitrification and DNRA resulted in increased NH4+-N levels. For this reason, DON and NH4+-N represented the highest proportion of N losses from the site. Some of the spatial and temporal variation of N concentrations was explained by correlations with selected chemical and hydro-topographical parameters (NO3--N/Cl- ratio, distance of the sampling point from the closest receptor, watertable depth, depth of sampling piezometer, DOC concentration). A high explanatory power of NO3--N/Cl- ratio and the distance of the sampling point from the closest receptor indicated the influence of point sources and groundwater-surface water interactions.