Now showing 1 - 10 of 19
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    Analysis of N2O emissions and isotopomers to understand nitrogen cycling associated with multispecies grassland swards at a lysimeter scale
    Nitrous oxide (N2O) is a potent greenhouse gas associated with nitrogen fertiliser inputs to agricultural production systems. Minimising N2O emissions is important to improving the efficiency and sustainability of grassland agriculture. Multispecies grassland swards composed of plants from different functional groups (grasses, legumes, herbs) have been considered as a management strategy to achieve this goal.
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    Managing legacy soil phosphorus in grassland soils for agricultural productivity and environmental quality: a review
    Phosphorus (P) is a lithophile element that tends to accumulate in the solid phase at the Earth’s surface and has a low water solubility. As P is a limiting nutrient for plant growth in most terrestrial systems, P in fertilizers has been a major factor underpinning global agricultural production in the 20th and early 21st centuries, including that from grassland. However, P is a costly farm input and it is also a finite mineral resource. Best agronomic practice is to maintain soil P levels at optimum over the medium-to-long term by managing P application and offtake. However, in some cases, soil P levels have been built up in excess of agronomic optimum due to P application driven by organic “waste disposal” or with the intention of building up a “bank” of soil P for future use. This has been associated with P losses to surface waters and impacts on water quality. Legislation, policy and best management practice advice in many countries has attempted to affect these legacy high P soils through a range of measures. In Ireland, for example, the Good Agricultural Practice measures, introduced in 2006 under the Irish Nitrates Action Plan, attempt to impose P deficits on soils with high P. National data shows that P fertilizer use declined by 55% on grassland soils between 2003 and 2008 and would suggest that soils with high soil P levels dropped from 30% in 2007 to 22% in 2011. This paper presents a review of the international literature on legacy excessive P in grassland soils, management practices and policy measures to manage them, and changes in soil P in response to such measures. Consideration is given to both agronomic and environmental concerns. There are a number of factors in grassland production systems, and particularly dairy production systems based on grazed grass, that differ from other agricultural production systems. For example, offtakes are typically lower than in tillage and the recycling of P, either by animal deposition or spreading of manures, gives less control to the farmer. Important questions addressed include: how quickly do grassland soil P levels decline under situations of negative P balance?; what fractions of P control soil P decline?; what grassland management practices are important in determining where and how fast soil P levels decline?; and what scale is appropriate to implement practice change and monitor effects?
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  • Publication
    Effects of mitigation measures on phosphorus loss across the transfer continuum from soil to water in a monitored dairy grassland catchment
    In many countries with intensive agriculture, water quality is a major issue and phosphorus (P) loss from soils to water is a major pressure. In Ireland, the EU Nitrates Directive Regulations aim to minimise these losses. This study measured the effects of P source management on P transfer across the nutrient transfer continuum from soils to water and subsequent water quality and agronomic impacts in a dairy-dominated, highly stocked and intensively monitored 7.6 km2 grassland catchment with mostly free draining soils over three years. Monitoring included farm P management, surface soil P concentrations, ground- and stream-water concentrations and stream flow. Reduced P source pressure was indicated by: a) lower farm-gate P balances (2.4 kg ha-1 yr-1), higher P use efficiencies (89%) and lower inorganic fertilizer P use (5.2 kg ha-1 yr-1) relative to previous studies, b) almost no P application during the winter to avoid incidental P transfers, and c) decreased proportions of soils with excessive P concentrations (32% to 24%). Over the same period, milk outputs of 14,585 l ha-1 and gross margins of €3,130 ha-1 indicated that production and profitability remained comparable with the top 10% of dairy farmers nationally. Declines in delayed flow and interflow pathway P concentrations during the winter months indicated some response in P delivery in surface water. However, delayed baseflows in the wetter third year resulted in elevated P concentrations and, overall, there were no clear trends in stream biological quality. This suggests that the impact of policy measures may be felt sooner closer to the source end of the nutrient transfer continuum, in soil P concentrations, for example, and a time lag may occur at the other end in P delivery to streams and stream biological quality, with implications for time frames of policy efficacy and policy monitoring.
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    Improving national mapping of critical source areas of phosphorus and nitrogen losses in Irish agricultural catchments to support policy
    Policymakers, farm advisors and water agencies require up-to-date national maps of critical source areas (CSAs) of nitrogen (N) and phosphorus (P) losses from agricultural land to improve catchment management decisions. The DiffuseTools project aimed to achieve this in Ireland by updating the existing Catchment Characterisation Tool and sub-model NCYCLE_IRL, which predicts environmental losses of N and P from the farm via surface runoff, leaching, denitrification and volatilisation. Updates included (i) using improved national maps of farm-scale source loadings as inputs, (ii) sub-field scale modelling of surface transport risk using soil topographic indices derived from 1 m and 5 m NEXTMap digital elevation models (DEMs), (iii) modelling hydrological disconnectivity from microtopography (HSA Index) and reinfiltration (SCIMAP), (iv) improving the national ditch and stream channel network used by the model by DEM extraction, and (v) using SCIMAP to improve predictions of erosion risk. The improved national source loading maps included mean nationally weighted farm-gate N and P imports (fertilizer, feed and livestock) and balance surpluses (kg/ha) calculated for each stocking rate and soil group (land use potential) category within each sector type (dairy, mixed livestock, suckler cattle, non-suckler cattle, sheep and tillage), using annual Teagasc National Farm Survey data (2008-15). Furthermore, updated national maps of soil P and atmospheric N and P deposition inputs were also used within the national source loading maps to improve model performance. National CSA maps for N and P for each pathway were then produced and evaluated using water quality monitoring data and field observations from the Environmental Protection Agency and Teagasc Agricultural Catchments Programme. These maps will be able to support sustainable intensification by informing farm and catchment management decisions such as where to cost effectively target mitigation measures to reduce environmental losses, where to distribute nutrient surpluses (to non-CSAs in nutrient deficit), and improving functional land management.
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    Benchmarking farm P and N management to improve agricultural sustainability
    Agriculture faces the challenge of achieving sustainable, profitable production while maintaining environmental quality. Conventional agricultural production is highly dependent on nutrient inputs of P and N in fertilizer and feed and poor use efficiency of these resources is associated with losses to the environment and impacts on water quality, GHG emissions, air quality, acidification and biodiversity. The AgriBenchmark project explored the possibilities for benchmarking of nutrient management performance on Irish farms.
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    Benchmarking P and N use efficiency in Irish farm systems to motivate practice change
    (The Organizing Committee of the 8th International Phosphorus Workshop, 2016-09-16) ; ;
    Agriculture faces the challenge of achieving sustainable, profitable production while maintaining environmental quality. In Ireland, for example, ambitious national growth targets for agricultural output have been set but, at the same time, Ireland, like other countries, must meet international environmental obligations in terms of water quality and greenhouse gas (GHG) emissions.
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    Phosphorus management, changes in soil P status over time and stream P loss in an intensive dairy catchment
    Phosphorus (P) inputs are vital to maintaining agronomically optimal levels of production in intensive, grazed, grass-based dairy production systems. However, P is a costly input and is also a finite mineral resource and mismanagement of P inputs has been associated with P losses to water and impacts on water quality. This paper presents results from the Agricultural Catchments Programme; an integrated advisory/research programme working with stakeholders to assess the efficacy of Ireland’s Good Agricultural Practice (GAP) measures in meeting the targets of the EU Nitrates and Water Framework Directives. Results are presented for field P sources, management and losses in the stream for a 7.6 km2 catchment dominated by intensive, grazed, grass-based dairy production on well drained soils with permeable geology. Phosphorus management and source pressures were characterised in terms of field-scale P inputs and balances, recorded on-farm, and surface soil P status, assessed by sampling at a resolution of <2 ha across the catchment. Changes in soil P status over time were assessed by re-sampling the same sample areas after three years. Phosphorus loss was characterised in terms of P concentration and loads monitored continuously with high-resolution bank-side analysers at the catchment outlet. Mean fertilizer and manure P field inputs in 2011 were 26.5 kg ha-1 (SD, 27.4). Most P (83 %) applied to grassland was in organic forms (slurry and farmyard manure). Peak P application was in February to May (63 %) with no P applied from late October to mid January. Initially, 30 % of soil samples had excessive P, but this decreased to 25 % over three years. Total stream P loss in 2010-2011 amounted to 0.54 kg ha-1 yr -1, with 62 % of this as reactive P. Results suggest that the GAP measures related to rates and timings of field P application are largely being followed, that soil P status would appear to be responding as intended, and that P losses in stream water are small relative to the quantity applied and, on balance, are likely to decrease over time in response to implementation of the GAP measures. This paper considers further implications for effectiveness of GAP measures, agronomically and environmentally, in intensive, grazed, grass-based dairy production systems, including appropriate scales for implementation and monitoring of GAP measures.
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    Managing Legacy Soil Phosphorus to Sustain Agriculture and Protect Water Quality
    A central tenet of modern nutrient management planning is the need to maintain soil phosphorus (P) in a range that optimizes crop production and protects water quality. Decades of research have identified the soil test P (STP) critical values needed for economically optimum crop yields, leading to well-established recommendations for efficient use of inorganic and organic P sources as soil amendments. However, in many areas of the USA and other countries, long-term over-application of animal manures and fertilizers has led to soil P accumulations to values that are considerably above agronomic optima and of concern for surface water quality. These soil P accumulations are a legacy of historically inefficient P management and present serious challenges to our efforts today to prevent nonpoint P pollution of surface waters. The fundamental issue identified in most research has been that it can take years, even decades, to decrease soil P values from “excessive” to “optimum”. Thus, even if P inputs to “high P” soils are restricted or eliminated, environmentally significant P losses to water may continue. For example, in Delaware, statewide summaries show ~60% of soils tested have STP values more than twice the critical value (~30 mg P kg-1 , Mehlich 3); in the intensive poultry producing regions, >30% of soils have STP values more than six times the critical value. A recent long-term (11 yr) cropping (corn-soy) study we conducted at two sites with initial Mehlich 3 P values of 98 and 70 mg kg-1 found that ceasing P applications decreased STP by 43% and 27%, with no negative effects on crop yields, providing guidance for emerging strategies for management of “high P” soils. Although similar long-term studies are somewhat rare, we have analyzed the findings of > 25 studies from the US and Europe investigating the relationship between P management, cropping system, and changes in amount and form of P in “high P” soils. Our presentation summarizes the findings of long-term P depletion studies in Delaware and our quantitative analyses of similar studies conducted in settings varying in initial STP, soil type, cropping system, and climate. We present strategies and policies to address the “legacy” P issue in overfertilized soils, toward a goal of sustaining soil P values in ranges optimum for crop production and protection of water quality.
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    Source partitioning using N2O isotopomers and soil WFPS to establish dominant N2O production pathways from different pasture sward compositions
    Nitrous oxide (N2O) is a potent greenhouse gas (GHG) emitted from agricultural soils and is influenced by nitrogen (N) fertiliser management and weather and soil conditions. Source partitioning N2O emissions related to management practices and soil conditions could suggest effective mitigation strategies. Multispecies swards can maintain herbage yields at reduced N fertiliser rates compared to grass monocultures and may reduce N losses to the wider environment. A restricted-simplex centroid experiment was used to measure daily N2O fluxes and associated isotopomers from eight experimental plots (7.8 m2) post a urea-N fertiliser application (40 kg N ha−1). Experimental pastures consisted of differing proportions of grass, legume and forage herb represented by perennial ryegrass (Lolium perenne), white clover (Trifolium repens) and ribwort plantain (Plantago lanceolata), respectively. N2O isotopomers were measured using a cavity ring down spectroscopy (CRDS) instrument adapted with a small sample isotope module (SSIM) for the analysis of gas samples ≤20 mL. Site preference (SP = δ15Nα – δ15Nβ) and δ15Nbulk ((δ15Nα + δ15Nβ) / 2) values were used to attribute N2O production to nitrification, denitrification or a mixture of both nitrification and denitrification over a range of soil WFPS (%). Daily N2O fluxes ranged from 8.26 to 86.86 g N2O-N ha−1 d−1. Overall, 34.2% of daily N2O fluxes were attributed to nitrification, 29.0% to denitrification and 36.8% to a mixture of both. A significant diversity effect of white clover and ribwort plantain on predicted SP and δ15Nbulk indicated that the inclusion of ribwort plantain may decrease N2O emission through biological nitrification inhibition under drier soil conditions (31%–75% WFPS). Likewise, a sharp decline in predicted SP indicates that increased white clover content could increase N2O emissions associated with denitrification under elevated soil moisture conditions (43%–77% WFPS). Biological nitrification inhibition from ribwort plantain inclusion in grassland swards and management of N fertiliser source and application timing to match soil moisture conditions could be useful N2O mitigation strategies.
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