• Ammonia emissions from urea, stabilized urea and calcium ammonium nitrate: insights into loss abatement in temperate grassland

      Forrestal, Patrick J.; Harty, Mary A.; Carolan, Rachael; Lanigan, Gary; Watson, C. J.; Laughlin, Ronald J.; McNeill, Gavin; Chambers, B. J.; Richards, Karl G.; Teagasc Walsh Fellowship Programme; et al. (Wiley, 17/11/2015)
      Fertilizer nitrogen (N) contributes to ammonia (NH3) emissions, which European Union member states have committed to reduce. This study focused on evaluating NH3-N loss from a suite of N fertilizers over multiple applications, and gained insights into the temporal and seasonal patterns of NH3-N loss from urea in Irish temperate grassland using wind tunnels. The fertilizers evaluated were calcium ammonium nitrate (CAN), urea and urea with the N stabilizers N-(n-butyl) thiophosphoric triamide (NBPT), dicyandiamide (DCD), DCD+NBPT and a maleic and itaconic acid polymer (MIP). 200 (and 400 for urea only) kg N/ha/yr was applied in five equal applications over the growing season at two grassland sites (one for MIP). Mean NH3-N losses from CAN were 85% lower than urea and had highly variable loss (range 45% points). The effect of DCD on NH3 emissions was variable. MIP did not decrease NH3-N loss, but NBPT caused a 78.5% reduction and, when combined with DCD, a 74% reduction compared with urea alone. Mean spring and summer losses from urea were similar, although spring losses were more variable with both the lowest and highest losses. Maximum NH3-N loss usually occurred on the second day after application. These data highlight the potential of stabilized urea to alter urea NH3-N loss outcomes in temperate grassland, the need for caution when using season as a loss risk guide and that urea hydrolysis in temperate grassland initiates quickly. Micrometeorological measurements focused specifically on urea are needed to determine absolute NH3-N loss levels in Irish temperate grassland.
    • Ammonia emissions from urea, stabilized urea and calcium ammonium nitrate: insights into loss abatement in temperate grassland

      Forrestal, Patrick J.; Harty, Mary A.; Carolan, Rachael; Lanigan, Gary; Watson, C. J.; Laughlin, Ronald J.; McNeill, Gavin; Chambers, B. J.; Richards, Karl G.; Department of Agriculture, Food and the Marine, Ireland; et al. (Wiley, 17/11/2015)
      Fertilizer nitrogen (N) contributes to ammonia (NH3) emissions, which European Union member states have committed to reduce. This study focused on evaluating NH3-N loss from a suite of N fertilizers over multiple applications, and gained insights into the temporal and seasonal patterns of NH3-N loss from urea in Irish temperate grassland using wind tunnels. The fertilizers evaluated were calcium ammonium nitrate (CAN), urea and urea with the N stabilizers N-(n-butyl) thiophosphoric triamide (NBPT), dicyandiamide (DCD), DCD+NBPT and a maleic and itaconic acid polymer (MIP). 200 (and 400 for urea only) kg N/ha/yr was applied in five equal applications over the growing season at two grassland sites (one for MIP). Mean NH3-N losses from CAN were 85% lower than urea and had highly variable loss (range 45% points). The effect of DCD on NH3 emissions was variable. MIP did not decrease NH3-N loss, but NBPT caused a 78.5% reduction and, when combined with DCD, a 74% reduction compared with urea alone. Mean spring and summer losses from urea were similar, although spring losses were more variable with both the lowest and highest losses. Maximum NH3-N loss usually occurred on the second day after application. These data highlight the potential of stabilized urea to alter urea NH3-N loss outcomes in temperate grassland, the need for caution when using season as a loss risk guide and that urea hydrolysis in temperate grassland initiates quickly. Micrometeorological measurements focused specifically on urea are needed to determine absolute NH3-N loss levels in Irish temperate grassland.
    • Can the agronomic performance of urea equal calcium ammonium nitrate across nitrogen rates in temperate grassland?

      Forrestal, Patrick J.; Harty, Mary A.; Carolan, Rachael; Watson, C. J.; Lanigan, Gary; Wall, David, P.; Hennessy, Deirdre; Richards, Karl G.; Teagasc Walsh Fellowship Programme; Department of Agriculture, Food and the Marine, Ireland; et al. (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.
    • Effects of urease and nitrification inhibitors on yields and emissions in grassland and spring barley

      Forrestal, Patrick J.; Wall, David; Carolan, Rachael; Harty, Mary A.; Roche, Leanne; Krol, Dominika; Watson, C. J.; Lanigan, Gary; Richards, Karl G.; Department of Agriculture, Food and the Marine, Ireland; et al. (International Fertiliser Society, 09/12/2016)
      In trials conducted in the temperate maritime climate of Ireland on a range of acidic soils, calcium ammonium nitrate (CAN) and urea gave comparable yield performance. There was little evidence of reduced yields by using urea for grassland or spring barley. Our finding that urea produced annual yields that were not significantly different from CAN differs from previous studies which found that yields from urea were lower than those from ammonium nitrate or nitrate based fertiliser in the UK. However, there are also published results from trials conducted in temperate Irish grassland showing equal yield performance of CAN and urea in the 1970s. Based on yield performance and the cost of fertiliser there is scope to dramatically increase the level of urea usage in straight and blended fertilisers in the temperate maritime climate of Ireland in both grassland and spring barley. Such an increase will bring substantial benefits in terms of reducing direct nitrous oxide (N2O) emissions from fertiliser applied to soil, particularly in poorly draining soils subject to high levels of precipitation. Nitrogen recovery by plants tends to be more sensitive to differences in fertiliser efficiency than is yield. Although yields did not differ between urea and CAN; urea had a lower nitrogen recovery indicating that urea usage will also result in a reduced level of fertiliser use efficiency. Reduced efficiency is less tangible to farmers who tend to be primarily concerned with dependable yield results. Reduced efficiency is a problem nonetheless, particularly as it is closely linked to NH3 emissions in urea usage. European countries including Ireland have committed to reduce national NH3 emissions to comply with the revised National Emission Ceilings Directive (2001/81/EC) in Europe. Increased urea usage, which looks attractive from a yield, cost and direct N2O perspective in Ireland, runs counter to meeting these commitments. Additionally, NH3 is a source of indirect N2O emissions that will negate some of the N2O savings from urea. Due to the issues of yield dependability, fertiliser efficiency, N2O and NH3 emissions the urease inhibitor N-(n-butyl) thiophosphoric triamide (NBPT) is a particularly attractive option for making urea use more efficient by addressing its key weakness in the area of variable NH3 loss and efficiency. The urease inhibitor NBPT along with the nitrification inhibitor dicyandiamide (DCD) were tested with urea in comparison with calcium ammonium nitrate (CAN). The nitrification inhibitor DCD was very effective in reducing fertiliser N associated N2O emissions. Indeed, its usage allowed N2O levels to be reduced to levels comparable to where no application of N fertiliser was made at some site-years. However, at the DCD incorporation rate tested, DCD contributed to variability in NH3 loss from urea and suppressed both yield response and fertiliser efficiency. Use of the urease inhibitor NBPT in addition to DCD went a substantial way to resolving these shortcomings. Continuing work is needed to tailor the rate of existing and new urease and nitrification inhibitors to optimise the balance between suppression of gaseous N emissions, agronomic performance and economic considerations.
    • Gross nitrogen transformations in grassland soil react differently to urea stabilisers under laboratory and field conditions

      Harty, Mary A.; McGeough, K. L.; Carolan, Rachael; Muller, Christoph; Laughlin, Ronald 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; et al. (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.
    • Improving and disaggregating N2O emission factors for ruminant excreta on temperate pasture soils

      Krol, Dominika; Carolan, Rachael; Minet, E.; McGeough, K. L.; Watson, C. J.; Forrestal, Patrick J.; Lanigan, Gary; Richards, Karl G.; Department of Agriculture, Food and the Marine, Ireland; RSF10/RD/SC/716; et al. (Elsevier, 11/06/2016)
      Cattle 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.
    • Reducing nitrous oxide emissions by changing N fertiliser use from calcium ammonium nitrate (CAN) to urea based formulations

      Harty, Mary A.; Forrestal, Patrick J.; Watson, C. J.; McGeough, K. L.; Carolan, Rachael; Elliott, C.; Krol, Dominika; Laughlin, Ronald J.; Richards, Karl G.; Lanigan, Gary; et al. (Elsevier, 04/05/2016)
      The 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.
    • Temperate Grassland Yields and Nitrogen Uptake Are Influenced by Fertilizer Nitrogen Source

      Harty, Mary A.; Forrestal, Patrick J.; Carolan, Rachael; Watson, C. J.; Hennessy, Deirdre; Lanigan, Gary; Wall, David; Richards, Karl G.; Department of Agriculture, Food and the Marine, Ireland; Teagasc Walsh Fellowship Programme; et al. (American Society of Agronomy, 25/01/2017)
      In 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.