The aim of the Teagasc Crops, Environment and Land Use Programme is to develop and transfer cost-effective crop production systems, along with evidence-based knowledge to support and underpin the development of an environmentally sustainable, competitive and profitable agri-food sector.

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  • Risk Assessment of E. coli Survival Up to the Grazing Exclusion Period After Dairy Slurry, Cattle Dung, and Biosolids Application to Grassland

    Ashekuzzaman, S. M.; Richards, Karl; Ellis, S; Tyrrel, S; O'Leary, E; Griffiths, Bryan; Ritz, K; Fenton, Owen; European Union; 265269 (Frontiers in Sustainable Food Systems, 10/07/2018)
    Grassland application of dairy slurry, cattle dung, and biosolids offers an opportunity to recycle valuable nutrients (N, P, and K), which may all introduce pathogens to the soil environment. Herein, a temporal risk assessment of the survival of Escherichia coli (E. coli) up to 40 days in line with the legislated grazing exclusion time points after application was examined across six scenarios: (1) soil and biosolids mixture, (2) biosolids amended soil, (3) dairy slurry application, (4) cattle dung on pasture, (5) comparison of scenario 2, 3, and 4, and (6) maximum legal vs. excess rate of application for scenario 2 and 3. The risk model input parameters were taken or derived from regressions within the literature and an uncertainty analysis (n = 1,000 trials for each scenario) was conducted. Scenario 1 results showed that E. coli survival was higher in the soil/biosolids mixture for higher biosolids portion, resulting in the highest 20 day value of residual E. coli concentration (i.e., C20, log10 CFU g−1 dw) of 1.0 in 100% biosolids or inoculated soil and the lowest C20 of 0.098 in 75/25 soil/biosolids ratio, respectively, in comparison to an average initial value of 6.4 log10 CFU g−1 dw. The E. coli survival across scenario 2, 3, and 4 showed that the C20 value of biosolids (0.57 log10 CFU g−1 dw) and dairy slurry (0.74 log10 CFU ml−1) was 2.9–3.7 times smaller than that of cattle dung (2.12 log10 CFU g−1 dw). The C20 values of biosolids and dairy slurry associated with legal and excess application rates ranged from 1.14 to 1.71 log10 CFU ha−1, which is a significant reduction from the initial concentration range (12.99 to 14.83 log10 CFU ha−1). The E. coli survival in un-amended soil was linear with a very low decay rate resulting in a higher C20 value than that of biosolids or dairy slurry. The risk assessment and uncertainly analysis showed that the residual concentrations in biosolids/dairy slurry applied soil after 20 days would be 45–57% lower than that of the background soil E. coli concentration. This means the current practice of grazing exclusion times is safe to reduce the risk of E. coli transmission into the soil environment.
  • Application of Dexter’s soil physical quality index: an Irish case study

    Fenton, Owen; Vero, Sara; Schulte, Rogier P. O.; O'Sullivan, Lilian; Bondi, G.; Creamer, Rachel E.; Department of Agriculture, Food and the Marine, Ireland; 6582 (Teagasc (Agriculture and Food Development Authority), Ireland, 26/08/2017)
    Historically, due to a lack of measured soil physical data, the quality of Irish soils was relatively unknown. Herein, we investigate the physical quality of the national representative profiles of Co. Waterford. To do this, the soil physical quality (SPQ) S-Index, as described by Dexter (2004a,b,c) using the S-theory (which seeks the inflection point of a soil water retention curve [SWRC]), is used. This can be determined using simple (S-Indirect) or complex (S-Direct) soil physical data streams. Both are achievable using existing data for the County Waterford profiles, but until now, the suitability of this S-Index for Irish soils has never been tested. Indirect-S provides a generic characterisation of SPQ for a particular soil horizon, using simplified and modelled information (e.g. texture and SWRC derived from pedo-transfer functions), whereas Direct-S provides more complex site-specific information (e.g. texture and SWRC measured in the laboratory), which relates to properties measured for that exact soil horizon. Results showed a significant correlation between S-Indirect (Si) and S-Direct (Sd). Therefore, the S-Index can be used in Irish soils and presents opportunities for the use of Si at the national scale. Outlier horizons contained >6% organic carbon (OC) and bulk density (Bd) values <1 g/cm3 and were not suitable for Si estimation. In addition, the S-Index did not perform well on excessively drained soils. Overall correlations of Si. with Bd and of Si. with OC% for the dataset were detected. Future work should extend this approach to the national scale dataset in the Irish Soil Information System.
  • The interactive effects of various nitrogen fertiliser formulations applied to urine patches on nitrous oxide emissions in grassland

    Krol, Dominika J.; Minet, E.; Forrestal, Patrick J.; Lanigan, Gary; Mathieu, O.; Richards, Karl J.; Department of Agriculture, Food and the Marine, Ireland; RSF10/RD/SC/716; 11S138 (Teagasc (Agriculture and Food Development Authority), Ireland, 19/09/2017)
    Pasture-based livestock agriculture is a major source of greenhouse gas (GHG) nitrous oxide (N2O). Although a body of research is available on the effect of urine patch N or fertiliser N on N2O emissions, limited data is available on the effect of fertiliser N applied to patches of urinary N, which can cover up to a fifth of the yearly grazed area. This study investigated whether the sum of N2O emissions from urine and a range of N fertilisers, calcium ammonium nitrate (CAN) or urea ± urease inhibitor ± nitrification inhibitor, applied alone (disaggregated and re-aggregated) approximated the N2O emission of urine and fertiliser N applied together (aggregated). Application of fertiliser to urine patches did not significantly increase either the cumulative yearly N2O emissions or the N2O emission factor in comparison to urine and fertiliser applied separately with the emissions re-aggregated. However, there was a consistent trend for approximately 20% underestimation of N2O loss generated from fertiliser and urine applied separately when compared to figures generated when urine and fertiliser were applied together. N2O emission factors from fertilisers were 0.02%, 0.06%, 0.17% and 0.25% from urea ± dicyandiamide (DCD), urea + N-(n-butyl) thiophosphoric triamide (NBPT) + DCD, urea + NBPT and urea, respectively, while the emission factor for urine alone was 0.33%. Calcium ammonium nitrate and urea did not interact differently with urine even when the urea included DCD. N2O losses could be reduced by switching from CAN to urea-based fertilisers.
  • Assessment of water-limited winter wheat yield potential at spatially contrasting sites in Ireland using a simple growth and development model

    Lynch, J. P.; Fealy, Reamonn; Doyle, D.; Black, L.; Spink, John; Department of Agriculture, Food and the Marine, Ireland (Teagasc (Agriculture and Food Development Authority), Ireland, 19/09/2017)
    Although Irish winter wheat yields are among the highest globally, increases in the profitability of this crop are required to maintain its economic viability. However, in order to determine if efforts to further increase Irish wheat yields are likely to be successful, an accurate estimation of the yield potential is required for different regions within Ireland. A winter wheat yield potential model (WWYPM) was developed, which estimates the maximum water-limited yield achievable, within the confines of current genetic resources and technologies, using parameters for winter wheat growth and development observed recently in Ireland and a minor amount of daily meteorological input (maximum and minimum daily temperature, total daily rainfall and total daily incident radiation). The WWYPM is composed of three processes: (i) an estimation of potential green area index, (ii) an estimation of light interception and biomass accumulation and (iii) an estimation of biomass partitioning to grain yield. Model validation indicated that WWYPM estimations of water-limited yield potential (YPw) were significantly related to maximum yields recorded in variety evaluation trials as well as regional average and maximum farm yields, reflecting the model’s sensitivity to alterations in the climatic environment with spatial and seasonal variations. Simulations of YPw for long-term average weather data at 12 sites located at spatially contrasting regions of Ireland indicated that the typical YPw varied between 15.6 and 17.9 t/ha, with a mean of 16.7 t/ha at 15% moisture content. These results indicate that the majority of sites in Ireland have the potential to grow high-yielding crops of winter wheat when the effects of very high rainfall and other stresses such as disease incidence and nutrient deficits are not considered.
  • A rapid and multi-element method for the analysis of major nutrients in grass (Lolium perenne) using energy-dispersive X-ray fluorescence spectroscopy

    Daly, Karen; Fenelon, A. (Teagasc (Agriculture and Food Development Authority), Ireland, 21/04/2017)
    Elemental analysis of grass (Lolium perenne) is essential in agriculture to ensure grass quality and animal health. Energy-dispersive X-ray fluorescence (EDXRF) spectroscopy is a rapid, multi-element alternative to current methods using acid digestion and inductively coupled plasma optical emission spectrometry (ICP-OES). Percentage phosphorus (P), potassium (K), magnesium (Mg) and calcium (Ca), determined from grass samples using EDXRF, were within 0.035, 0.319, 0.025 and 0.061, respectively, of ICP-OES values. Concordance correlation coefficients computed using agreement statistics ranged from 0.4379 to 0.9669 (values close to one indicate excellent agreement); however, the level of agreement for each element depended on the calibrations used in EDXRF. Empirical calibrations gave excellent agreement for percentage P, K and Ca, but moderate agreement for percentage Mg due to a weaker correlation between standards and intensities. Standardless calibration using the fundamental parameters (FP) approach exhibited bias, with consistently lower values reported for percentage P and Mg, when compared with ICP-OES methods. The relationship between the methods was plotted as scatter plots with the line of equality included, and although correlation coefficients indicated strong relationships, these statistics masked the effects of consistent bias in the data for percentage P and Mg. These results highlight the importance of distinguishing agreement from correlation when using statistical methods to compare methods of analysis. Agreement estimates improved when a matching library of grass samples was added to the FP method. EDXRF is a comparable alternative to conventional methods for grass analysis when samples of similar matrix type are used as empirical standards or as a matching library.
  • Genomic prediction of crown rust resistance in Lolium perenne

    Arojju, Sai Krishna; Conaghan, Patrick; Barth, Susanne; Milbourne, Dan; Casler, Michael D.; Hodkinson, Trevor R.; Michel, Thibauld; Byrne, Stephen L.; Department of Agriculture, Food and the Marine, Ireland; Marie Sklodowska-Curie; Teagasc Walsh Fellowship Programme Ireland; RSF 11/S/109; 658031; 658031 (Biomed Central, 29/05/2018)
    Background Genomic selection (GS) can accelerate genetic gains in breeding programmes by reducing the time it takes to complete a cycle of selection. Puccinia coronata f. sp lolli (crown rust) is one of the most widespread diseases of perennial ryegrass and can lead to reductions in yield, persistency and nutritional value. Here, we used a large perennial ryegrass population to assess the accuracy of using genome wide markers to predict crown rust resistance and to investigate the factors affecting predictive ability. Results Using these data, predictive ability for crown rust resistance in the complete population reached a maximum of 0.52. Much of the predictive ability resulted from the ability of markers to capture genetic relationships among families within the training set, and reducing the marker density had little impact on predictive ability. Using permutation based variable importance measure and genome wide association studies (GWAS) to identify and rank markers enabled the identification of a small subset of SNPs that could achieve predictive abilities close to those achieved using the complete marker set. Conclusion Using a GWAS to identify and rank markers enabled a small panel of markers to be identified that could achieve higher predictive ability than the same number of randomly selected markers, and predictive abilities close to those achieved with the entire marker set. This was particularly evident in a sub-population characterised by having on-average higher genome-wide linkage disequilibirum (LD). Higher predictive abilities with selected markers over random markers suggests they are in LD with QTL. Accuracy due to genetic relationships will decay rapidly over generations whereas accuracy due to LD will persist, which is advantageous for practical breeding applications.
  • Transforming Sitka spruce plantations to continuous cover forestry

    Wilson, Edward; Short, Ian; Ní Dhubháin, Áine; Purser, Paddy; Teagasc; RMIS 0138 (Select Media, 2018-03)
    Identifying potential crop trees and regular thinning are the keys to successful transformation of plantations to resilient, continuous cover forests. By Edward Wilson, Ian Short, Áine Ní Dhubháin and Paddy Purser.
  • Ensifer-mediated Arabidopsis thaliana Root Transformation (E-ART): A Protocol to Analyse the Factors that Support Ensifer-mediated Transformation (EMT) of Plant Cells

    Rathore, Deeraj Singh; Doohan, Fiona M.; Mullins, Ewen; Teagasc Walsh Fellowship Programme (Bio-protocol LLC, 05/10/2017)
    Ensifer adhaerens OV14, a soil borne alpha-proteobacteria of the Rhizobiaceae family, fortifies the novel plant transformation technology platform termed ‘Ensifer-mediated transformation’ (EMT). EMT can stably transform both monocot and dicot species, and the host range of EMT is continuously expanding across a diverse range of crop species. In this protocol, we adapted a previously published account that describes the use of Arabidopsis thaliana roots to investigate the interaction of A. thaliana and Agrobacterium tumefaciens. In our laboratory, we routinely use A. thaliana root explants to examine the factors that enhance the utility of EMT. In addition, the E-ART protocol can be used to study the transcriptional response of E. adhaerens and host plant following exposure to explant tissue, the transformability of different Ensifer adhaerens strains/mutants as well as testing the susceptibility of A. thaliana mutant lines as a means to decipher the mechanisms underpinning EMT.
  • Quantitative trait loci associated with different polar metabolites in perennial ryegrass - providing scope for breeding towards increasing certain polar metabolites

    Foito, Alexandre; Hackett, Christine A; Stewart, Derek; Velmurugan, Janaki; Milbourne, Dan; Byrne, Stephen L; Barth, Susanne; Department of Agriculture, Food and the Marine, Ireland; RSF 06–346 (Biomed Central, 10/10/2017)
    Background Recent advances in the mapping of biochemical traits have been reported in Lolium perenne. Although the mapped traits, including individual sugars and fatty acids, contribute greatly towards ruminant productivity, organic acids and amino acids have been largely understudied despite their influence on the ruminal microbiome. Results In this study, we used a targeted gas-chromatography mass spectrometry (GC-MS) approach to profile the levels of 25 polar metabolites from different classes (sugars, amino acids, phenolic acids, organic acids and other nitrogen-containing compounds) present in a L. perenne F2 population consisting of 325 individuals. A quantitative trait (QTL) mapping approach was applied and successfully identified QTLs regulating seven of those polar metabolites (L-serine, L-leucine, glucose, fructose, myo-inositol, citric acid and 2, 3-hydroxypropanoic acid).Two QTL mapping approaches were carried out using SNP markers on about half of the population only and an imputation approach using SNP and DArT markers on the entire population. The imputation approach confirmed the four QTLs found in the SNP-only analysis and identified a further seven QTLs. Conclusions These results highlight the potential of utilising molecular assisted breeding in perennial ryegrass to modulate a range of biochemical quality traits with downstream effects in livestock productivity and ruminal digestion.
  • Phylogenetic and functional potential links pH and N2O emissions in pasture soils

    Samad, Sainur; Biswas, Ambarish; Bakken, Lars R.; Clough, Timothy J.; de Klein, Cecilia A.M.; Richards, Karl G.; Lanigan, Gary J.; Morales, Sergio E.; New Zealand Fund for Global Partnerships in Livestock Emissions Research (Nature Publishing Group, 26/10/2016)
    Denitrification is mediated by microbial, and physicochemical, processes leading to nitrogen loss via N2O and N2 emissions. Soil pH regulates the reduction of N2O to N2, however, it can also affect microbial community composition and functional potential. Here we simultaneously test the link between pH, community composition, and the N2O emission ratio (N2O/(NO + N2O + N2)) in 13 temperate pasture soils. Physicochemical analysis, gas kinetics, 16S rRNA amplicon sequencing, metagenomic and quantitative PCR (of denitrifier genes: nirS, nirK, nosZI and nosZII) analysis were carried out to characterize each soil. We found strong evidence linking pH to both N2O emission ratio and community changes. Soil pH was negatively associated with N2O emission ratio, while being positively associated with both community diversity and total denitrification gene (nir & nos) abundance. Abundance of nosZII was positively linked to pH, and negatively linked to N2O emissions. Our results confirm that pH imposes a general selective pressure on the entire community and that this results in changes in emission potential. Our data also support the general model that with increased microbial diversity efficiency increases, demonstrated in this study with lowered N2O emission ratio through more efficient conversion of N2O to N2.
  • Carbon cycling in temperate grassland under elevated temperature

    Jansen-Willems, Anne B.; Lanigan, Gary; Grunhage, Ludger; Muller, Christoph; Department of Agriculture, Food and the Marine, Ireland; Teagasc Walsh Fellowship Programme; RSF 10/SC/716 (Wiley, 01/11/2016)
    An increase in mean soil surface temperature has been observed over the last century, and it is predicted to further increase in the future. The effect of increased temperature on ecosystem carbon fluxes in a permanent temperate grassland was studied in a long-term (6 years) field experiment, using multiple temperature increments induced by IR lamps. Ecosystem respiration (R-eco) and net ecosystem exchange (NEE) were measured and modeled by a modified Lloyd and Taylor model including a soil moisture component for R-eco (average R2 of 0.78) and inclusion of a photosynthetic component based on temperature and radiation for NEE (R2 = 0.65). Modeled NEE values ranged between 2.3 and 5.3 kg CO2 m−2 year−1, depending on treatment. An increase of 2 or 3°C led to increased carbon losses, lowering the carbon storage potential by around 4 tonnes of C ha−1 year−1. The majority of significant NEE differences were found during night-time compared to daytime. This suggests that during daytime the increased respiration could be offset by an increase in photosynthetic uptake. This was also supported by differences in δ13C and δ18O, indicating prolonged increased photosynthetic activity associated with the higher temperature treatments. However, this increase in photosynthesis was insufficient to counteract the 24 h increase in respiration, explaining the higher CO2 emissions due to elevated temperature.
  • Vegetative propagation of dieback-tolerant Fraxinus excelsior on

    Douglas, Gerry C.; Namara, J.M.; O'Connell, K.; Dunne, L.; Grant, Jim; European Co-Operation in Science and Technology; FP1103 (Swedish University of Agricultural Sciences, 2017)
    Ash trees which are tolerant to Hymenoscyphus fraxineus may be selected in all age classes among heavily infected populations. They may be produced also by controlled crossings of disease tolerant trees, because the genetic component of inheritance for disease tolerance is high. For mature and juvenile plant material, the deployment of disease tolerant genotypes could be potentially achieved by vegetatively propagating selected genotypes. We describe a system to vegetatively propagate selected ash genotypes and we discuss the prospects and options for using vegetative propagation on all age classes of trees. Mature trees were rejuvenated through the process of micropropagation to establish mother plants in large trays which were cut back repeatedly (hedged) to produce at least two crops of cuttings per year. The rooting capacity of ten genotypes was tested by a commercial nursery over a period of three years, to assess the feasibility of using hedged mother plants for efficient propagation. Commercial practise was to treat cuttings with 0.25% IBA, insert them in plug pots and maintain them covered with fine plastic within low plastic tunnels in a non heated greenhouse and without supplementary heating at the cutting base. In the first year, the mean rooting rate was 53 % for the first crop of cuttings and 35 % for the second. In the second and third years the rooting rates improved to over 80% for each crop of cuttings as experience was gained in handling the material. Rooting rate varied among the genotypes. We assessed the growth and development of micropropagated ash trees in the field from an observation clonal trial, consisting of four mature genotypes which had been established in 2002 in five replicate plots. The micropropagated trees were generally similar in height and dbh to seed derived control trees and developed normally. These observations are discussed in the context of using vegetative propagation as a tool in breeding and for the large scale deployment of ash with tolerance to H. fraxineus.
  • Ash dieback on the island of Ireland

    McCracken, A.R.; Douglas, Gerry C.; Ryan, C.; Destefanis, M.; Cooke, L.R.; European Co-Operation in Science and Technology (Swedish University of Agricultural Sciences, 2017)
    On the island of Ireland it is estimated that there are over half a million kilometres of hedgerows (400,000+ km in the Republic of Ireland (Rep. Ireland) and 113,000+ in Northern Ireland (Northern Ireland). Ash (Fraxinus excelsior) is the second most important component, after hawthorn (Crataegus monogyna), in large proportions of this hedgerow network. In the Rep. Ireland over 20,000 ha of ash have been planted since 1990, primarily for sawlogs and to provide material for the manufacture of hurleys, which are used in an important national sport called hurling, and for camogie sticks used to play camogie. Ash dieback, caused by Hymenoscyphus fraxineus, was first identified on the island in October 2012 and since then has been detected at 306 sites (195 in Rep. Ireland and 111 in Northern Ireland). In the vast majority of cases the outbreaks have been on young, imported trees planted within the previous 5 – 6 years and it was evident that the pathogen had been introduced on trees for planting. On a small number of occasions there was evidence of the pathogen cycling within a plantation or moving from the plantation to infect neighbouring hedgerow trees. One possible mechanism by which the pathogen can build up sufficient inoculum is by the formation of apothecia on infected woody tissue high up on the plants. Rep. Ireland and Northern Ireland have strict policies of eradication and containment, as set out in the All-Ireland Chalara Control Strategy. To date over 2.1 million trees have been destroyed as part of an eradication strategy. It is considered that this prompt and far-reaching action has had a significant impact, significantly mitigating and preventing the rapid establishment of the pathogen and limiting its spread. The interventions since the disease was first confirmed have helped to protect the considerable investment in ash plantations of the last 20 years. The pathogen has not, however, been eradicated from the island of Ireland and it remains to be seen how widespread, and how quickly ash dieback will become established on the island of Ireland. The latest figures from the Republic of Ireland are that 733 hectares of ash plantation has been reconstituted with another species as a result of Chalara and this has cost our state €2.6 million so far; in addition, Chalara has been found and confirmed in all 26 counties of the Republic of Ireland to a greater or lesser extent. As a result the current policies and procedures regarding Chalara are under review.
  • Multiple viral infections in Agaricus bisporus - Characterisation of 18 unique RNA viruses and 8 ORFans identified by deep sequencing

    Deakin, Gregory; Dobbs, Edward; Bennett, Julie M.; Jones, Ian M.; Grogan, Helen M.; Burton, Kerry S.; Teagasc Walsh Fellowship Programme; European Commission; 201043; 286836 (Nature Publishing Group, 26/05/2017)
    Thirty unique non-host RNAs were sequenced in the cultivated fungus, Agaricus bisporus, comprising 18 viruses each encoding an RdRp domain with an additional 8 ORFans (non-host RNAs with no similarity to known sequences). Two viruses were multipartite with component RNAs showing correlative abundances and common 3′ motifs. The viruses, all positive sense single-stranded, were classified into diverse orders/families. Multiple infections of Agaricus may represent a diverse, dynamic and interactive viral ecosystem with sequence variability ranging over 2 orders of magnitude and evidence of recombination, horizontal gene transfer and variable fragment numbers. Large numbers of viral RNAs were detected in multiple Agaricus samples; up to 24 in samples symptomatic for disease and 8–17 in asymptomatic samples, suggesting adaptive strategies for co-existence. The viral composition of growing cultures was dynamic, with evidence of gains and losses depending on the environment and included new hypothetical viruses when compared with the current transcriptome and EST databases. As the non-cellular transmission of mycoviruses is rare, the founding infections may be ancient, preserved in wild Agaricus populations, which act as reservoirs for subsequent cell-to-cell infection when host populations are expanded massively through fungiculture.
  • Can the agronomic performance of urea equal calcium ammonium nitrate across nitrogen rates in temperate grassland?

    Forrestal, Patrick J.; Harty, M.A.; Carolan, R.; Watson, C.J.; Lanigan, Gary; Wall, D.P.; Hennessy, Deirdre; Richards, Karl G.; Teagasc Walsh Fellowship Programme; Department of Agriculture, Food and the Marine, Ireland; Department of Agriculture, Environment and Rural Affairs, Northern Ireland (Wiley, 23/03/2017)
    In temperate grassland, urea has been shown to have lower nitrous oxide emissions compared to ammonium nitrate-based fertilizer and is less expensive. However, nitrogen (N) loss via ammonia volatilization from urea raises questions regarding yield performance and efficiency. This study compares the yield and N offtake of grass fertilized with urea, calcium ammonium nitrate (CAN) and urea treated with the urease inhibitor N-(n-butyl) thiophosphoric triamide (NBPT) at six site-years. Five annual fertilizer N rates (100–500 kg N/ha) were applied in five equal splits of 20–100 kg N/ha during the growing season. On average, urea produced slightly better yields than CAN in spring (103.5% of CAN yield) and slightly poorer yields in summer (98.4% of CAN yield). There was no significant difference in annual grass yield between urea, CAN and urea + NBPT. Urea had the lowest cost per tonne of DM grass yield produced. However, the urea treatment had lower N offtake than CAN and this difference was more pronounced as the N rate increased. There was no difference in N offtake between urea + NBPT and CAN. While this study shows that urea produced yields comparable to CAN, urea apparent fertilizer N recovery (AFNR) tends to be lower. Urea selection in place of CAN will increase national ammonia emissions which is problematic for countries with targets to reduce ammonia emissions. Promisingly, NBPT allows the agronomic performance of urea to consistently equal CAN across N rates by addressing the ammonia loss limitations of urea.
  • Gross nitrogen transformations in grassland soil react differently to urea stabilisers under laboratory and field conditions

    Harty, M.A.; McGeough, K.L.; Carolan, R.; Muller, C.; Laughlin, R.J.; Lanigan, Gary; Richards, Karl G.; Watson, C.J.; Department of Agriculture, Food and the Marine, Ireland; Department of Agriculture, Environment and Rural Affairs, Northern Ireland; Teagasc Walsh Fellowship Programme; RSF10-/RD/SC/716; RSF11S138) (Elsevier, 10/02/2017)
    A laboratory and a field study were conducted on a permanent grassland soil in Northern Ireland to investigate the effects of urea in combination with N process inhibitors such as the urease inhibitor N-(butyl) thiophosphoric triamide (NBPT) and/or the nitrification inhibitor dicyandiamide (DCD) on soil N dynamics. Urea enriched with n-butyl 15N to 60 atom % was applied to soil at a rate of 100 μg N g−1 dry soil in the laboratory and 100 kg N ha−1 in the field. A numerical 15N tracing model was used to quantify several simultaneously occurring gross N transformation rates in both studies. The changes in soil nitrate (NO3−) and ammonium (NH4+) concentrations and 15N enrichment over a 25-day period as well as the concentration and 15N enrichment of plant N at harvest were used to model soil gross N transformations. The results showed that the effect of N process inhibitors varied firstly between laboratory and field studies and secondly whether the inhibitors were applied individually or in combination. Overall DCD had a greater effect on the major soil N transformations than NBPT; reducing oxidation of NH4+, total nitrification, net NO3− produced, total mineralisation and the net adsorption of NH4+ at both laboratory and field scale. The effect of DCD was similar for these transformations whether applied alone or co-applied with NBPT. In contrast NBPT had no significant effect on oxidation of NH4+, total nitrification, total mineralisation or total immobilisation compared to urea in the field, while the effect on these transformations in the laboratory was significant. The contrasting effects of inhibitors on gross N transformations between laboratory and field may relate to the differences in experimental conditions, e.g. soil preparation, environmental conditions and the contribution of plant biomass. To obtain a more realistic assessment of gross soil N transformations in situ, it is essential that laboratory experiments are supplemented with field studies.
  • Groundwater nitrate reduction versus dissolved gas production: A tale of two catchments

    McAleer, E.B.; Coxon, C.E.; Richards, Karl G.; Jahangir, M.M.R.; Grant, Jim; Mellander, Per-Erik; Teagasc Walsh Fellowship Programme (Elsevier, 20/02/2017)
    At the catchment scale, a complex mosaic of environmental, hydrogeological and physicochemical characteristics combine to regulate the distribution of groundwater and stream nitrate (NO3−). The efficiency of NO3− removal (via denitrification) versus the ratio of accumulated reaction products, dinitrogen (excess N2) & nitrous oxide (N2O), remains poorly understood. Groundwater was investigated in two well drained agricultural catchments (10 km2) in Ireland with contrasting subsurface lithologies (sandstone vs. slate) and landuse. Denitrification capacity was assessed by measuring concentration and distribution patterns of nitrogen (N) species, aquifer hydrogeochemistry, stable isotope signatures and aquifer hydraulic properties. A hierarchy of scale whereby physical factors including agronomy, water table elevation and permeability determined the hydrogeochemical signature of the aquifers was observed. This hydrogeochemical signature acted as the dominant control on denitrification reaction progress. High permeability, aerobic conditions and a lack of bacterial energy sources in the slate catchment resulted in low denitrification reaction progress (0–32%), high NO3− and comparatively low N2O emission factors (EF5g1). In the sandstone catchment denitrification progress ranged from 4 to 94% and was highly dependent on permeability, water table elevation, dissolved oxygen concentration solid phase bacterial energy sources. Denitrification of NO3 − to N2 occurred in anaerobic conditions, while at intermediate dissolved oxygen; N2O was the dominant reaction product. EF5g1 (mean: 0.0018) in the denitrifying sandstone catchment was 32% less than the IPCC default. The denitrification observations across catchments were supported by stable isotope signatures. Stream NO3− occurrence was 32% lower in the sandstone catchment even though N loading was substantially higher than the slate catchment.
  • A field-based comparison of ammonia emissions from six Irish soil types following urea fertiliser application

    Burchill, William; Lanigan, Gary; Forrestal, Patrick J.; Reville, F.; Misselbrook, T.; Rochards, Karl G.; Department of Agriculture, Food and the Marine, Ireland; RSF 13/S/430 (Teagasc (Agriculture and Food Development Authority), Ireland, 30/12/2016)
    Ammonia (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.
  • 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 T.; 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.
  • Visual drainage assessment: A standardised visual soil assessment method for use in land drainage design in Ireland

    Tuohy, P.; Humphreys, James; Holden, N.M.; O'Loughlin, James; Reidy, B.; Fenton, Owen T. (Teagasc (Agriculture and Food Development Authority), Ireland, 20/08/2016)
    The implementation of site-specific land drainage system designs is usually disregarded by landowners in favour of locally established ‘standard practice’ land drainage designs. This is due to a number of factors such as a limited understanding of soil–water interactions, lack of facilities for the measurement of soil’s physical or hydrological parameters and perceived time wastage and high costs. Hence there is a need for a site-specific drainage system design methodology that does not rely on inaccessible, time-consuming and/or expensive measurements of soil physical or hydrological properties. This requires a standardised process for deciphering the drainage characteristics of a given soil in the field. As an initial step, a new visual soil assessment method, referred to as visual drainage assessment (VDA), is presented whereby an approximation of the permeability of specific soil horizons is made using seven indicators (water seepage, pan layers, texture, porosity, consistence, stone content and root development) to provide a basis for the design of a site-specific drainage system. Across six poorly drained sites (1.3 ha to 2.6 ha in size) in south-west Ireland a VDA-based design was compared with (i) an ideal design (utilising soil physical measurements to elucidate soil hydraulic parameters) and (ii) a standard design (0.8 m deep drains at a 15 m spacing) by model estimate of water table control and rainfall recharge/drain discharge capacity. The VDA method, unlike standard design equivalents, provided a good approximation of an ideal (from measured hydrological properties) design and prescribed an equivalent land drainage system in the field. Mean modelled rainfall recharge/drain discharge capacity for the VDA (13.3 mm/day) and ideal (12.0 mm/day) designs were significantly higher (P < 0.001, s.e. 1.42 mm/day) than for the standard designs (0.5 mm/day), when assuming a design minimum water table depth of 0.45 m.

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