Search

Organic carbon (C) plays an essential role in the denitrification process as it supplies energy for N2O, N2 and CO2 producing reactions. The objectives of this study were to: (i) rank the reactivity of different C compounds found in manures based on their availability for denitrification and (ii) explore C-quality in different C sources based on their capacity to promote denitrification. Evaluation of different C-sources in promoting denitrification was conducted based on the molar ratio of CO2 production to NO3− reduction after incubation. Results of the first experiment (a 12-day investigation) showed that glucose and glucosamine were highly reactive C compounds with all applied NO3− being exhausted by day 3, and glucosamine had significantly high amount of NH4+-N present at end of the experiment. The glucose and glucosamine treatments resulted in significantly greater cumulative CO2 production, compared to the other treatments. In the second experiment (a 9-day investigation), all NO3− had been depleted by day 6 and 9 from acetic acid and glucose, respectively, and the greatest cumulative CO2 production was from acetic acid. The CO2 appearance to NO3− molar ratios revealed that glucose and glucosamine were compounds with highly available C in the first experiment. In the second experiment, the pig slurry and acetic acid were found to be C-sources that promoted potential denitrification. The application of slurry to soil results in the promotion of denitrification and this depends on the availability of the C compounds it contains. Understanding the relationship between C availability and denitrification potential is useful for developing denitrification mitigation strategies for organic soil amendments.

National and international requirements for greenhouse gas emissions demand the development of more accurate inventories and mitigation options that are effective in reducing emissions. The UK government set a target for the year 2050 of an 80% reduction in greenhouse gas emissions compared to the 1990 baseline. Estimate of UK national emissions is based on IPCC default methodology and as agriculture contributes about 7% of total GHG emissions of which 60% is N2O, efforts to improve the inventory and assess mitigation options are needed. Models can be used to derive N2O emission factors providing high spatial and temporal resolution. In this study, we used two models, the UK-DNDC, a mechanistic model to estimate N2O emissions from soils and the NITCAT model to estimate the fraction of N applied that is leached and causes indirect emissions, both at county level for the UK. Four mitigation options were assessed and the results showed there were differences in the emission factors according to location. Average emission factors for N2O from soils for inorganic fertiliser did not differ from the IPCC default value but for organic fertiliser the model gave much lower values. FracLEACH for arable land was higher than that for grassland (UK averages of 0.28 and 0.09 respectively) and the national average value was 0.18. For N2O, the most effective mitigation measure was adjusting fertiliser rates to account for crop available manure N. For N leaching, the most effective measure was implementation of a manure closed period.

Nitrous oxide (N2O) is of major importance as a greenhouse gas and precursor of ozone (O3) destruction in the stratosphere mostly produced in soils. The soil-emitted N2O is generally predominantly derived from denitrification and, to a smaller extent, nitrification, both processes controlled by environmental factors and their interactions, and are influenced by agricultural management. Soil water content expressed as water-filled pore space (WFPS) is a major controlling factor of emissions and its interaction with compaction, has not been studied at the micropore scale. A laboratory incubation was carried out at different saturation levels for a grassland soil and emissions of N2O and N2 were measured as well as the isotopocules of N2O. We found that flux variability was larger in the less saturated soils probably due to nutrient distribution heterogeneity created from soil cracks and consequently nutrient hot spots. The results agreed with denitrification as the main source of fluxes at the highest saturations, but nitrification could have occurred at the lower saturation, even though moisture was still high (71 % WFSP). The isotopocules data indicated isotopic similarities in the wettest treatments vs. the two drier ones. The results agreed with previous findings where it is clear there are two N pools with different dynamics: added N producing intense denitrification vs. soil N resulting in less isotopic fractionation.

This study reports the leaching of nitrogen (N), phosphorus (P) and potassium (K) from beneath grazed leguminous swards established at two Mediterranean and two north-western European sites. The purpose of the experiment was to provide scientific evidence on whether moderately extensive systems of animal production based on legumes could be environmentally sustainable, to comply with the Water Framework Directive. There were differences in the legume species and the grazing animal between sites, reflecting differences in local management and climatic conditions. There were also differences in the methods used to assess nutrient leaching, again reflecting soil and hydrological conditions present. There were no general differences between the quantities of nutrient leached at Mediterranean and north European sites over the 3 year experiment and these quantities, up to 6 kg ha -1 year -1 for nitrate-N, were similar to those reported from earlier studies of leaching beneath grasswhite clover swards at temperate sites. Temporal variability in leached nutrient concentrations and amounts was greater at the Mediterranean sites. There were no discernible differences in the effects of sward treatment on leaching. The proportion of N leached in organic combination or as ammonium was greater than with N-fertilized grass systems. The quantities of P leached were relatively high, ranging from 0AE1 to 3 kg ha) 1 year) 1 for soluble reactive P, reflecting the practice of high levels of fertilizer application to these systems. Reduction of P transfer to water from these systems will be critical for future compliance with the Water Framework Directive.

As much as 60% of the nitrate in water in England is thought to derive from agriculture. Legislation aims to improve water quality by limiting nitrate concentration in surface and groundwaters to 50 mg l −1 . The UK Government responded to the requirements of the EC Nitrate Directive by delineating Nitrate Vulnerable Zones (NVZs) to cover 55% of England in 2002 and increased it to 70% in 2009. In this study we assessed the cost-effectiveness of measures for implementation in livestock systems to mitigate nitrate leaching in the UK. These estimates were prepared for a range of hypothetical farms representative of typical dairy, beef and sheep farms at different locations in England and Wales and for a list of mitigation measures identified to reduce leaching. The NGAUGE and NFixCycle models were used to estimate leaching from these systems. The costs of implementation of the mitigation measures were also assessed in order to evaluate the cost-effectiveness of these measures. In general, the most effective measures to reduce leaching for all systems were the ones that involved a reduction in stocking rates and grazing time, followed by those involving improvements in fertiliser and crop management. Only in the case of the dairy system was effectiveness affected by location of the farm. The costs for implementation in the sheep system were relatively low compared with beef and dairy systems. Implementation of some of the measures with high cost-effectiveness would need to be incentivised financially or with legislation due to the high costs involved.

Multiple demands are placed on farming systems today. Society, national legislation and market forces seek what could be seen as conflicting outcomes from our agricultural systems, e.g. food quality, affordable prices, a healthy environmental, consideration of animal welfare, biodiversity etc., Many of these demands, or desirable outcomes, are interrelated, so reaching one goal may often compromise another and, importantly, pose a risk to the economic viability of the farm. SIMS DAIRY , a farm-scale model, was used to explore this complexity for dairy farm systems. SIMS DAIRY integrates existing approaches to simulate the effect of interactions between farm management, climate and soil characteristics on losses of nitrogen, phosphorus and carbon. The effects on farm profitability and attributes of biodiversity, milk quality, soil quality and animal welfare are also included. SIMS DAIRY can also be used to optimise fertiliser N. In this paper we discuss some limitations and strengths of using SIMS DAIRY compared to other modelling approaches and propose some potential improvements. Using the model we evaluated the sustainability of organic dairy systems compared with conventional dairy farms under non-optimised and optimised fertiliser N use. Model outputs showed for example, that organic dairy systems based on grass-clover swards and maize silage resulted in much smaller total GHG emissions per l of milk and slightly smaller losses of NO 3 leaching and NO x emissions per l of milk compared with the grassland/maize-based conventional systems. These differences were essentially because the conventional systems rely on indirect energy use for ‘fixing’ N compared with biological N fixation for the organic systems. SIMS DAIRY runs also showed some other potential benefits from the organic systems compared with conventional systems in terms of financial performance and soil quality and biodiversity scores. Optimisation of fertiliser N timings and rates showed a considerable scope to reduce the (GHG emissions per l milk too).

Cardenas, L. M., Thorman, R., Ashlee, N., Butler, M., Chadwick, D., Chambers, B., Cuttle, S. C., Donovan, N., Kingston, H., Lane, S., Dhanoa, M. S., Scholefield, D. (2010). Quantifying annual N2O emission fluxes from grazed grassland under a range of inorganic fertiliser nitrogen inputs. Agriculture, Ecosystems & Environment, 136(3-4), 218-226. Sponsorship: BBSRC; Grant (BB/D010683/1) IMPF: 02.79

A variety of options exist for mitigation of greenhouse gas (GHG) emissions from agriculture. This paper discusses the use of the SIMSDAIRY modelling framework to analyse the whole-systems response to different methods, acting singly or in combination, to mitigate GHG emissions from a typical dairy farm in the UK. These methods comprise farm management changes, new technologies and/or plant and/or animal new functional traits focused on mitigating GHG. Different functional units were used in order to ensure that the different aspects of the farm performance were analyzed in the most relevant way (e.g. concentration of NO3− in leachate or kg GHG emitted per unit of milk). Examples of the methods that were tested and discussed are some relating fertilization, diet, systematic and genetic changes in the system. We conclude that the effectiveness of the combined GHG mitigation methods cannot be assessed simply by adding the effectiveness of each method applied singly. Effective GHG mitigation methods may in some cases increase emissions of other forms of pollution and have very different impact on farm profitability. This study also evidences the importance of selecting the right unit of reference to measure efficacy to reduce GHG emissions and highlights the importance to integrate this type of study with socio-economic studies in order to assess the full potential of these mitigation methods.

Nitrous oxide (N2O) affects climate change as a greenhouse gas and indirectly contributes to stratospheric ozone depletion. The main source of N2O in soils is denitrification which requires high soil moisture, carbon and nitrate. Nitrification inhibitors can be used to mitigate emissions of N2O from soils. In Portugal, fertilisers are often applied when soils are still relatively warm and moist conditions conducive to denitrification. A Portuguese arable soil was inhibited with dicyandiamide, a nitrification inhibitor and the effect on soil microbiological activity and composition was determined after 46 days. Soils were then incubated and received carbon and ammonium under high soil water conditions and mineral N and N2O fluxes were measured during 22 days. We found that dicyandiamide decreased microbial populations and activity, but did not alter composition. Pre-conditioning of the soil with dicyandiamide was 80% more effective in reducing fluxes of N2O than simultaneous application with fertiliser.

SUMMARYCurrently, society awareness, legislations and competing markets demand dairy farming systems which are sustainable. In the near future, farm management and animal genetics will be key elements in developing such sustainability. Although the effect of farm management on some attributes of sustainability has already been studied, the impacts and scope for realizing goals of agricultural multifunctionality through genetic changes are still to be tested. Sustainable and Integrated Management Systems for Dairy Production (SIMSDAIRY) is a new farm level modelling framework which integrates these concepts to practical actions and brings all of this complexity into an operational and scientific modus operandi.The current paper provides a brief description of the structure of SIMSDAIRY and an example of how it can be used to compare the scope for improving the overall sustainability of a dairy farm by: (i) future system changes aimed at improving genetic characteristics of plants and animals with (ii) current system structural changes aimed at improving nutrient management efficiency. In order to do this comparison, management factors and new genetic traits from plants or/and animals, acting singly or in combination, are evaluated against a baseline dairy farm scenario. Sustainability is measured in terms of targets associated with: (i) the Nitrates Directive, (ii) phosphorus (P) threshold for eutrophication, (iii) the Kyoto Protocol, (iv) the Gothenburg Protocol, (v) an adequate net farm income for standard of living and acceptable standards of (vi) quality of milk, (vii) animal welfare, (viii) level of biodiversity, (ix) landscape aesthetics and (x) soil quality.Results suggest that genetic-based changes offer greater scope than management-based ones to improve sustainability up to an acceptable level. Costs associated with management changes are often too high within current socio-economics circumstances. Optimizing nitrogen (N) mineral fertilizer rate and timing was the only management-based measure that, while improving most of the environmental and biodiversity indices, resulted in improved economic results. Some genetic-based changes offered substantial scope for reducing environmental losses while having economic benefits. However, only those decreasing the crude protein (CP) of the plant and increasing the diet N cow partition into milk seemed to result in non-significant pollution swapping and be achievable in the nearby future.

We describe a new farm scale model to optimize management of UK dairy farming systems in order to meet environmental and economic targets. The effect of abatement measures for nitrate (NO 3 ) leaching on the emissions of nitrous oxide (N 2 O) and methane (CH 4 ) and the economic output of a dairy farm was investigated using this model. The model is a useful tool to evaluate potential pollution swapping when applying abatement measures.

The rate and extent to which cattle or pig slurry infiltrates into soil after application is one of the important factors determining the rate and extent of subsequent ammonia (NH 3 ) volatilization. Better characterization of the infiltration process is required to improve predictive models of NH 3 losses after land spreading. This paper describes a laboratory system using time domain reflectometry to measure slurry infiltration into soil columns. This system enabled semi-continuous, non-destructive infiltration measurements to be made, assessing the influence of slurry type, dry matter (DM) content, soil type and soil water tension. Differences were noted in the infiltration behaviour of cattle and pig slurries. For cattle slurry, DM content (range 1.7-7.1%) was the main influencing factor. Infiltration rate rapidly decreased with increasing DM content and there was no influence of soil type or water tension. For pig slurry, all of the slurry infiltrated into a sandy clay loam soil within the first hour, regardless of DM content (range 1.5-4.7%), whereas only 60% infiltrated into a clay loam soil over the same time period (slurry DM content 2.1%).

Several long-term sets of hourly nitrate concentration data were obtained through deployment of a nitrate sensor in an upper reach of the River Taw, a small moorland-fed river in the South West of the UK. Examination of the data obtained during periods of low flow and the absence of rainfall in the catchment revealed the presence of marked diurnal cycles, which were in concert and negatively correlated with diurnal cycles in water temperature. After verifying that these cycles were natural, an intensive 90-h field monitoring campaign was conducted, in which river water was sampled hourly and immediately analysed in the laboratory for molybdate-reactive phosphorus (P), nitrate, nitrite, ammonium, and pH. Coincident measurements of water temperature, river discharge and solar energy were also taken at, or close to, the site. All measurements revealed diurnal patterns and all patterns were concerted. The cycles of P, nitrate, nitrite, and discharge had two maxima and minima per 24 h, while the cycle of water temperature had one, with a maximum at 20.00 and a minimum at 08.00. The amplitudes of the cycles of P and nitrate were each about 30% of the mean values, while the amplitude of the nitrite cycle was as great as 80% of the mean value on occasions. Both biological and physical mechanisms for the cycling could operate through water temperature and/or incident radiation to account for the observed phenomenon, but there remains uncertainty of which is the more important. The observations have important implications for both the accuracy of pollution assessment in rivers and the physiological rhythms of riverine organisms.

Ammonia (NH3) emissions from cattle are much less when they are grazing than when they are housed. The urine excreted during grazing may rapidly infiltrate soil whereas it remains on the surface of impermeable floors and yards. If the average grazing season for the UK herd could be extended from 6 to 8 months, NH3 emissions from cattle could potentially be reduced by ca. 15% (of the total for all livestock) if the cattle spend all of the extra grazing days outdoors. The main objective of this desk study was to assess the potential of extended season grazing to reduce NH3 emissions from UK cattle farming. The impacts on nitrate (NO3−) leaching and nitrous oxide (N2O) emissions were also estimated. A simple process-based model was developed to quantify the potential for extending the grazing season. A farm-scale model of NH3 emissions at the farm-scale, based on published emission factors for UK agriculture, was used to estimate NH3 emissions. Losses of NO3− following slurry spreading were estimated using the MANNER model, while NO3− leaching and denitrification losses during grazing were taken from output by the NGAUGE model. We conclude that one month’s extra grazing (based on the animals being outside for all of that month, day and night,) may reduce NH3 emissions from slurry-based systems by ca. 9% and for FYM-based systems by ca. 7% compared with losses from the current ca. 180-day winter housing period. However, in practice cattle are not outdoors all day during the extended grazing period. If it is assumed that cattle graze for an average of 4 h per day over the extended period, then the monthly reduction in NH3 emissions may be only ca. 1–2%. At all sites most of this conserved N was predicted to be lost as NO3−. For slurry-based systems this could be at least 80%. For FYM-based systems, for which there was less potential to conserve NH3, the increase in NO3− leaching was always greater than the NH3 conserved. The effects on direct emissions of N2O were estimated be negligible, if grazing began earlier in spring or perhaps some reduction when grazing continues for longer in autumn. We conclude that extending the grazing season will increase NO3− leaching and that further studies are needed to fully evaluate the potential for reducing emissions of NH3.

The distribution and impacts of different nitrogen pollutants are inextricably linked. To understand the problem fully, the interactions between the different pollutants need to be taken into account. This is particularly important when it comes to abatement techniques, since measures to reduce emissions of one nitrogen pollutant can often lead to an increase in another. This project represents a step towards greater understanding of these issues by linking together new and existing nitrogen flux models into a larger framework. The modelling framework has been constructed and some of the nitrogen flows between fields, farms and the atmosphere have been modelled for a UK study area for typical farm management scenarios.

Phosphate selective electrodes have been produced based upon rubbery membranes containing heterocylic macrocycles as sensors covalently bound to a cross-linked polystyrene-block–polybutadiene-block – polystyrene (SBS) polymer. The membranes were robust and the best HPO 4 2− -selective membrane fabricated was composed of 7.1% (m/m) dicumyl peroxide, 28.3% (m/m) 2-nitrophenyloctylether, 9.8% (m/m) 3-(10-undecenyl)-1,5,8-triazacyclodecane-2,4-dione, 31.0% (m/m) SBS and 23.8% (m/m) PoleStar™ 200R (clay-based filler). The characteristics of this electrode were a linear Nernstian range of 3.9×10 −3 to 1×10 −6 mol dm −3 HPO 4 2− with a limit of detection of 1.0×10 −6 mol dm −3 HPO 4 2− , a slope of −29.7±0.9 mV per activity decade and a pH range from 6 to 8. Selectivity coefficients for phosphate against various interfering anions (chloride, sulfate and nitrate) were determined. Response times were 2 min or under, stability of response and electrode lifetime in continuous use were also very satisfactory. The response behavior of HPO 4 2− -ISEs based upon mobile and bound ionophores was comparable and suggests that mobility of the ionophore is not necessary to obtain a working ISE and that covalent binding of ionophores can be used to produce ISEs of increased stability and robustness.

A model (MAST) to calculate the mass flow of NH3 through amodel dairy farm has been developed. Updated emission factors for UKagriculturewere used to examine different abatement strategies available for a typicaldairy farm. A range of annual NH3 emissions was calculated for bothslurry and FYM based dairy systems. Emission for the slurry based system ranged between 27 kg NH3-N ha−1 yr−1, achieved using a combination of abatementstrategies, and 107 kg NH3-N ha−1 yr−1, calculated for a ‘worst case’scenario. For FYM, this range was between 33 and 86 kg NH3-Nha−1 yr−1. The greatest reductionswereachieved by manipulating options linked to fertiliser usage and manureapplication.

A large soil block was constructed to determine the importance of preferential flow routes compared with matric flow pathways at a pasture site in mid-Devon. The sandy loam soil was well structured and uniform. The soil block measured 5 m x 3 m × 1m and was instrumented with an array of 54 tensiometers, TDR wave guides and suction samplers connected to an in situ chloride analysis system. Four steady state irrigation experiments were conducted with a range of rainfall intensities. During each experiment chloride and nitrate tracers were applied and the patterns of movement were observed. Although the application of tracer was uniform and the soil was relatively homogeneous, there was large variability across the block in terms of time taken to reach the peak concentration (TPC) and the peak concentration itself. About 44 samplers operated at the greatest intensities (10-2 mm h - 1 ) and only 35 at the smallest (1 mm h -1 ). No relationship was found between TPC and depth. The fastest TPC and largest concentrations were associated with the greatest rainfall intensities. Relative importance of the individual water pathways was a function of soil heterogeneity: parts of the soil block were highly active with several pathways having short TPCs and conductivities in excess of 4 m day -1 whereas other areas had longerTPCs and conductivities of 1-2 m day -1 . The pattern was also dynamic, with conductivities of the pathways changing through time, though most of the faster pathways maintained their greater conductivities for more than one year.

Past research on nitrogen (N) inputs, losses and surpluses focused on separate components of grassland management, i.e., grazed or cut swards and the impact of fertiliser or slurry applications. In practice, however, grassland is both grazed and cut for conservation, and N fertiliser is supplied from both organic and inorganic sources. A whole systems approach was used to evaluate the effects of combinations of management strategies designed to reduce N losses on N budgets, and herbage and animal production in South West England. Three systems with contrasting N inputs were compared: CN, conventional mineral N application and broadcast slurry; TN, tactical mineral N application with slurry injection and the early housing of cattle; GC, a mixed grass/white clover sward with no mineral N addition and slurry injection. Comparisons were made on two contrasting soil types: a freely-draining sandy loam (Gleysol, Site 1), and a poorly drained clay (Luvisol, Site 2). 1 ha farmlets were grazed to a target sward height by beef cattle for a 5-year (Site 1) or a 4-year (Site 2) period. Herbage surplus to grazing requirements was cut for silage. On average, 185 kg N ha 1 was applied annually to treatment TN compared with 280 kg N ha 1 for CN. An additional 76, 102 and 67 kg N ha 1 was applied in slurry to treatments CN, TN and GC, respectively. Substantial reductions in N surpluses were achieved for both treatments TN and GC compared with treatment CN (N surpluses ha 1 : 254, 168 and 119 kg at Site 1, and 247 kg, 190 and 73 kg at Site 2, for CN, TN and GC, respectively). The highest N input for treatment CN was associated with the greatest animal and herbage production. More land was required for grazing on treatment GC and less herbage was cut for silage so that self-sufficiency was not attained for winter fodder on this treatment. The early removal of cattle on treatment TN did not result in a significant increase in the amount of herbage cut for silage. It was concluded that the combinations of mitigation options used were successful in reducing N surpluses compared with the conventional N management system, but animal and herbage production was reduced. © 2000 Elsevier Science B.V. All rights reserved.

The composition of dissolved organic matter (DOM) in a soil is the product of a variety of soil processes. Changes in the composition of DOM in water discharged from soil should, therefore, give an important insight into modifications in these soil processes. We hypothesise that these processes in soils, under different grassland management regimes, would be affected to different extents by the short-term disturbance of a storm event and that evidence of this could be detected in delta(13)C and delta(15)N signatures in drainage and surface runoff waters. During a storm event we collected discharge waters from 1 ha grassland lysimeters, with or without artificial drainage, which received contrasting fertiliser inputs, and delta(13)C and delta(15)N signatures were determined. Changes in (13)C enrichment during the storm event were clearly identifiable, as were differences between plots for (13)C and (15)N, illustrating that this technique has potential to be a useful tool for identifying and investigating short- and long-term changes in soil organic matter dynamics. Copyright 1999 John Wiley & Sons, Ltd.

Techniques to provide a quantitative description of soil structure in a reasonable time scale using equipment that is widely available are examined. Three complementary techniques for quantifying soil structure within the pore size range from 136 to 4000 μm (equivalent diameter) are evaluated for two isolated, unsaturated soil blocks (0.85 m3). Profile tracing and binary transect methods were used to examine the pore sizes >1000 μm. Pore sizes

Continuous daily determinations of nitrate were made during a 6 week period with a novel nitrate sensitive electrode deployed in V-notch weirs draining grassland lysimeter plots. The sensor molecule, triallyldecylammonium nitrate was covalently bound to an acrylonitrile–butadiene co-polymer to obtain a robust, rubbery membrane that was incorporated into a commercially obtainable electrode body. A nitrate determination assembly was constructed by interfacing the electrode with a double-junction reference electrode and a temperature probe, through a pre-amplifier to a hand-held digital readout and battery pack. One assembly was positioned in each of two V-notch weirs, receiving drainage water with different nominal ranges of nitrate concentration; set 1, 3–20 ppm and set 2, 0.7–5.1 ppm nitrate-N. Despite conditions conducive to rapid chemical and microbiological degradation, all electrodes remained physically intact, maintained nitrate sensitivity without drift and followed the trends in nitrate concentration well. The electrode performance was compared with laboratory automated chemical determinations made on contemporaneous samples of drainage water.

Organic farming practice prohibits the use of triple superphosphate (TSP) as a source of phosphorus. As basic slag is not now generally available, interest is focused on the relative value of ground rock phosphate (GRP). A comparison of TSP and Gafsa GRP was made during 1988–92 as to their ability to increase DM production under cutting from newly sown grass/white clover swards established in 1987 on an acid clay soil in SW England. Averaged over the different P fertiliser inputs and years, the DM yield was 8.0 t ha-1 y-1 (range 6.93–9.81) compared to 6.3t ha-1y-1 (range 6.00–7.71) without added P. Lime was added at either 3 or 6t ha-1 in 1987, and at half these rates in 1990. Whereas the yield improved by 45% with P at the lower rate of lime, it improved only by 12% at the higher rate. When P fertiliser was applied annually at 30 kg ha-1, TSP was superior to GRP, but when applied in one initial dose of 120 kg ha-1, GRP was superior over the subsequent 4 year period. There was no consistent effect of the addition of either P or lime on the clover content of the sward. The alkaline bicarbonate soil test (Olsen P) was a good predictor of available P within a given year; there was a general reduction of P availability over the course of the experiment. Mechanisms to explain the longer term effectiveness of GRP are postulated and discussed. It is concluded that farmers who are limited to using GRP rather than TSP would suffer a yield penalty over the longer term of 11.5%, and that P fertilizer for the ley phase in a rotation should be incorporated in one dose at the outset.

Annual liveweight gain of beef cattle (steers) grazing grass pasture fertilized with 200 kg N/ha was compared over a period of 7 years (1989–95) with that of steers grazing grass/white clover pasture given no artificial N fertilizer at North Wyke, Devon, UK. Nitrogen lost by leaching over the ensuing winter drainage periods was monitored from both pastures. Nitrogen leaching loss from the fertilized pasture over an extended period of 13 years (1983–95) is also reported.The average annual liveweight gain of the steers grazing the grass/clover pasture (0·81 t/ha) was 19% lower than that of the steers grazing the N-fertilized grass pasture (1·00 t/ha). The average annual loss of nitrate-N by leaching in winter drainage from the grass/clover pasture (13 kg/ha) was only 26% of that recorded from the fertilized grass (50 kg/ha). A possible reason for this difference may arise from the previous history of the grass/clover pasture which had been ploughed in 1982, causing a flush of N mineralization and consequently greater immobilization of N in the soil in subsequent years.Losses of N each winter by leaching measured over a 13-year period from the fertilized grass were highly correlated (P

Nitrate leaching from a double-cropping forage system was measured over a 2-year period (June 1994–May 1996) in the Northwest region of Portugal using ceramic cup samplers. The crops were grown for silage making and include maize (from May to September) and a winter crop (rest of the year) consisting of a mixture of cereals and Italian ryegrass. The experiment was performed on two different sites with a history of many years under the same crop and fertiliser management, but differing in the amounts of N applied as fertiliser and by regular cattle slurry applications. The annual nitrate leaching losses measured ranged from 154 to 338 kg N ha-1. These amounts lead to annual mean concentrations between 22 and 41 mg \(NO_3^ - \)-N L-1 in the drained water. The coarse textured soils (sandy loams) and the climatic conditions of the region with more than 600 mm of drainage concentrated between October and March, tended to promote the leaching of all the nitrate-N left in the soil after the maize crop plus the N released by mineralization during the winter period. On these soils, the minimum amount of drainage (necessary to provide the complete leaching of all the nitrate-N in the soil profile in the end of summer), seems to be between 300 and 400 mm. The winter crops removed important quantities of N (83–116 kg N ha-1) but, due to their late establishment in autumn they did not succeed in taking up the nitrate-N left in the soil after the maize crop. Approaches for reducing the nitrate leaching losses in this particular system are discussed.

The feasibility of adopting an empirical approach to predicting peak nitrate concentrations in water draining agricultural land is examined in the light of the relationships derived from leaching experiments on a range of soils, and from river data for England and Wales for the period 1974–1986. Well-fitted linear regressions were obtained of peak nitrate concentration in leachate on the annual load of leachable nitrate in the soil. The slopes to the regressions ranged in value from greater than 1.3 for measurements in shallow soils over limestone in a low rainfall area, to 0.25 for a well-structured clay soil with mole drainage in a high rainfall area. (A slope of 1.0 means that a load of 100 kg N ha−1 gives rise to a peak concentration of 100 mg N 1−1). This range mainly reflected the ranges in soil water capacity and degree of preferential flow occurring during drainage. The slopes to the regressions for river waters were consistently smaller than those for clay soils in the same areas. The slopes for rivers draining mainly low-lying clay or chalk catchments in drier areas (Thames, Anglian and Southern Water Authority areas) were generally greater than those for rivers draining mainly wetter and more upland areas (South West and Welsh Water Authority areas). The differences between the slopes to the regressions for rivers could be partly accounted for by differences in average rainfall, suggesting possible effects from systematic differences in land use, soil structure and date of rewetting of soils in different climatic areas. The regressions indicated that peak concentrations in excess of the European Community limit (11.3 mg 1−1 nitrate-N) might be associated with total nitrate loads in rivers draining clay catchments of 30 kg N hat in central and eastern England, or greater than 70 kg N ha−1 in Wales. The results indicate that the regressions for soils might form the basis of a catchment-scale model of nitrate leaching, provided that it is linked with a hydrogeological sub-model that accounts for the contribution to river discharge from upland and groundwater sources, and for the effects of different land uses on the timing of the peak nitrate concentrations.

Although the loss of P in agricultural runoff can provide freshwater eutrophication, little information is available on losses from permanent grasslands. Thus, 14 lysimeter plots (each of 1 ha), established in 1982 on a clay loam soil under grazed grassland management, were monitored between 1989 and 1991 for release of molybdate-reactive phosphorus (MRP). The plots enabled the daily measurement of discharge through field drains (to 85 cm) or by surface lateral runoff (to 30 cm). Sward type was either perennial ryegrass (Lolium perenne L.) or a perennial ryegrass-clover (Trifolium sp.) mixture. The plots were grazed continuously by beef cattle and received either 200 or 400 kg N ha -1 yr -1 in various combinations. Having collected >7500 data points during the 3 yr, it was found that there was no significant difference between the effects of either agronomic or drainage variables (P > 0.05) within years. However, there was a significant difference (P < 0.05) between drainage variables when the data from the 3 yr were combined, as there were larger MRP losses from undrained treatments. There was no relationship between concentration of MRP and drainage volume. The MRP concentrations ranged from 0.01 to 0.7 mg L -1 with an average concentration of 0.02 mg L -1 . Losses of MRP as great as 0.4 kg ha -1 yr -1 were measured in surface lateral runoff from undrained plots and 0.2 kg ha -1 yr -1 in water percolating through field drains. The data show this type of grassland system may have the potential to be an important diffuse source of P to fresh waters.

The independent comparison of a three-dimensional data set from a large soil block (5 m × 3 m × 1 m) with output from a one-dimensional model of soil water and solute transport (LEACHC) is considered. The lack of work comparing site-specific solute breakthrough with model predictions is outlined. A statistical method of limiting the number of runs required to provide a good representation of model output based on Response Surface Methodology is presented. This method is both a sensitivity analysis, and a means of identifying how a model behaves. As an example the model LEACHC was tested using response surface methodology and was found to be insensitive to input variable alteration. A lack of compatibility between sampling methods and the assumptions of the model may account for it being unable to predict solute movement similar to that measured in a large soil block. It is concluded that the technique presented is well suited to testing one-dimensional models.

A proportion of the nitrogen (N) applied to grasslands as organic or inorganic fertilizers can be lost to water courses as nitrate and to the atmosphere as nitrous and nitric oxides. Volcanic soils from Chile are not generally prone to leaching, possibly due to net immobilization of nitrate and/or ammonium, and/or due to inhibition of nitrification by either chemical or physical processes. In laboratory studies we found large mineralization potentials in soils from three different Chilean soils after 17 weeks of incubation, totalling 215 and 254 mg kg−1 dry soil for two Andisols and 127 mg kg−1 dry soil in an Ultisol. Nitrification occurred after a short period, and was lowest in the Ultisol. In addition, microbial analysis showed nitrifiers to be present in all three soils. Adsorption of ammonium was two-fold stronger than for nitrate, ranging from 29 to 180 kg N ha−1. The highest potential for N adsorption in the 0–60 cm soil profile was with the Ultisol (398 kg N ha−1), but was similar in both...

Studies were made to assess the losses of nutrients in runoff from pastures, and to ascertain whether application of N as NH4 rather than NO3 both reduced N losses and enhanced yields of herbage. Two experiments were conducted during consecutive springs in which surface lysimeter plots were established on sloping grassland with soils of low permeability, and different forms of fertiliser applied for first-cut silage. Despite weather conditions conducive to large nutrient losses, less than 10% of the N applied was found in runoff. However, the peak concentrations of nutrients were large relative to standards for good water quality. The concentrations of NO3-N were greater in water from plots that received NH4 NO3 than from those that received either (NH4)3 PO4 or urea. Large concentrations of NH4-N were measured in runoff in response to all treatments, with the largest in water from plots that received urea. The mechanisms that may account for the observed resistance to loss in runoff are discussed. In the first experiment there was no advantage (or disadvantage) in applying an (NH4)3 PO4 formulation 2 weeks earlier than applying either NH4 NO3 or urea. In the second experiment, where all treatments were applied on the same dates, herbage mass accumulated more slowly on plots that received NH4 NO3 compared to those that received more NH4-rich forms. However, in neither experiment did the fertiliser treatments influence the yields of herbage cut for silage.

Cet article decrit un modele simulant le cycle de l'azote a l'echelle d'une parcelle de prairie pâturee, inclus dans un modele de gestion a l'echelle du bassin, susceptible de decrire la charge et la concentration des nitrates dans les rivieres. Le modele comprend deux sous-modeles de transport des nitrates: l'un reliant la concentration des nitrates dans les eaux drainees a travers differents types de sols a la quantite de nitrates stockes dans ces sols, le second prenant en compte la fraction de roches permeables du bassin. Le sous-modele calculant l'approvisionnement et le transport des nitrates du sol repond aux variations climatiques annuelles selon un schema fonde sur le maximum du deficit en eau du sol. Les previsions du modele ont ete confrontees aux meilleures estimations de la charge annuelle et de la concentration de pointe de 11 rivieres du Royaume Uni drainant de petits bassins versants a dominante herbeuse pour la periode allant de 1974 a 1987.

The leaching of nitrate from soil to ground and surface waters is now limited by European legislation to protect human drinking water. Much long term monitoring and short term experimentation has been undertaken using fertilisers and nitrate tracers to understand how transport occurs. A paper test‐strip technology, used in conjunction with a modern hand‐held reflectometer was tested and utilised to permit fine spatial and temporal resolution analysis of nitrate breakthrough in a large undisturbed soil block. It was found that characteristic types of breakthrough occurred in the soil block, and that a fine resolution picture of the breakthrough curve could easily be established without recourse to sample storage and laboratory analysis. The techniques proved cost effective and had the added benefit of stopping locally generated toxic waste. It is concluded that paper test‐strip technology is highly suited to monitoring research where strong concentration tracers are used.

This paper describes the computer controlled data acquisition systems designed to obtain fine spatial and temporal resolution data of tracer in soil water within a large undisturbed soil block. Such information is desirable to help understand and model transport mechanisms in light of increasingly strict environmental pollution limits. The soil block was 5.4 × 3.4 × 1.2 m, instrumented in nine layers with time domain reflectometry (TDR) waveguides multiplexed using a PC; pressure transducer equipped tensiometers multiplexed using a datalogger and suction samplers connected to in situ flow-injection analysis systems controlled by a PC. A rainfall simulator capable of applying tracer to the block without altering the surface flux (which could range from 1 to 30 mm h −1 ) was controlled by a datalogger. Initial conditions when the soil block was subjected to a surface flux of 10 mm h −1 are presented along with an example of a chloride breakthrough curve to illustrate the nature of the data obtained from the soil block system. It is concluded that the integrated system described is a significant advance in working technology for field and plot scale tracer experiments because the spatial and temporal resolutions achieved are possible with a single person maintaining the system.

The dynamics of mineral N species involved in the processes of denitrification were studied in laboratory systems using a soil from permanent pasture. Experiments were carried out to test a mechanistic model linking C mineralization and denitrification. This involved the use of competitive Michaelis-Menten type enzyme kinetics to simulate the reduction of NO−3 and the formation of NO−2, N2O and N2. The rate of reduction of each N oxide was assumed to be dependent upon its concentration and on a weighting factor for competition between electron acceptors. Concentrations of 20, 200 and 2000mg NO−3 kg−1 were applied to a soil slurry and anaerobically incubated for 5 days at 25°C. The production of CO2, N2O and N2, and concentrations of NO−3 and NO−2 were monitored daily. The ratio between CO2 produced and nitrate reduced was 0.7; much lower than the value expected if glucose was the only C substrate and all nitrate was reduced to N2. The nitrite concentration remained below 0.5 mg NO−2Nkg−1 in each treatment indicating that all NO−2 formed, was very rapidly reduced to N2O. The reduction of N2O was much slower: no N2 was formed within the first day when 200 mg NO−3-N kg− was applied, and the rate of N2O production remained higher than the rate of N2O reduction for the first 4 days of the incubation. Only 75% of the N2O formed was reduced within 1 day when 20 mg NO−3-N kg−1 was added. The dynamics of the different forms of nitrogen generated in the denitrification process at different concentrations of available nitrate could be simulated using a weighting factor or an affinity of 1 for NO−3, around 1000 for NO−2 and 0.75 for N2O. It was not necessary to include inhibitory effects of nitrate or nitrite in the model to simulate the observed patterns of mineral N dynamics. It was concluded from this study that low affinity for N2O as compared to the high affinity for NO−2 could lead to high losses of nitrous oxide in the field even if only low quantities of NO−3 were available.

SUMMARY Drained and undrained grassland lysimeter plots were established in 1982 on a clay loam of the Hallsworth series at a long-term experimental site in south-west England. The plots were continuously grazed by beef cattle, and received fertilizer at either 200 or 400 kg N ha-1 per annum to the existing permanent sward, or at 400 kg N ha-1 to a new sward, reseeded to perennial ryegrass following cultivation. Drainage water was monitored at V-notch weirs and sampled daily for the analysis of nitrate-N. Seven years of data are presented (five years for the reseeded swards). On the drained plots a large proportion of the rainfall was routed preferentially down large pores to the mole drains, whilst on the undrained plots, drainage was mainly by surface runoff. The average quantities of nitrate N leached per year were 38.5, 133.8 and 55.7 kg ha-1 from the old sward that received 200 and 400 kg N ha-1, and from the reseed that received 400 kg N ha-1 fertilizer, respectively. Ploughing and reseeding resulted in a two-fold reduction in leaching, except during the first winter after ploughing, and twice as much leaching occurred after a hot, dry summer as after a cool, wet one. Nitrate concentrations in drainage from either drained or undrained plots were rather insensitive to rainfall intensity, such that concentration was a good predictor of nitrate load for a given drainage volume. The drainage volume determined the proportion of the leachable N that remained in the soil after the winter drainage period. Initial (peak) concentrations of nitrate N ranged, on average, from 55 mg dm-3 for the drained old sward that received 400 kg N ha-1 fertilizer, to 12 mg dm-3 for the undrained sward at 200 kg N ha-1 fertilizer input. Concentrations of nitrate N in drainage from similar, unfertilized plots rarely exceeded 1 mg dm-3. The results suggest that manipulating the nitrate supply can lessen leaching and that the route of water through soil to the watercourse determines the maximum nitrate concentration for a given load.

Studies were carried out on experimental pasture plots which are drained or undrained and receiving 0, 200 and 400 kg N ha−1 yr−1 as inorganic fertilizer. Earthworm populations (dominated by Lumbricus rubellus and Aporrectodea caliginosa) were lowest (71.0± 11.4 g m−2) on the undrained ON plots and highest (100.3 ± 13.4 g m−2) on the undrained 200N plots. Deep burrowing species appear to be excluded from colonizing the drained plots by the high water-table during winter and spring. Aggregations of earthworms beneath dung pats were recruited laterally peaking at a population equivalent of 417.5 ±60 g m−2 after 63 days. Local burrowing activities resulted in increased macroporosity over a period of 105 days. Earthworm casts were found to have 3–5 times higher denitrification rates than surrounding soil with lower endogenous rates of N2O production. Denitrification was determined by cast NO3-N content and fertilizer applications. Earthworm casts may make a significant contribution to the heterogeneity associated with field measurements of denitrification. Lysimeter studies were also carried out using soil monoliths to investigate the effects of earthworms (including Lumbricus terrestris) on nutrient leaching from treatments receiving the equivalent of 200 g N ha−1 as cattle slurry or inorganic fertilizer. Nitrate concentrations in leachates were low in the unfertilized treatments but earthworms increased losses three times. Nitrate losses were higher in the slurry treatments, possibly because of damage to the sward, with proportionally smaller earthworm effects. It is concluded that the moderate population densities of surface active species still have detectable effects on the hydrology and mineral N fluxes in intensively managed pastures although their effects on sward production are negligible in relation to the main plot treatments. Earthworm activity may be an important determinant of heterogeneity in the rates of soil processes.

A long-term field grazing experiment was begun in 1982 to examine the impact of efficient field drainage on herbage and animal production from swards on an impermeable clay loam in the south-west of England. Drained and undrained lysimeter plots (each of 1 ha) were established on the existing permanent sward and received annual applications of fertilizer N of 200 or 400 kg ha−1. Similar plots were initially ploughed and reseeded with Lolium perenne (cv. Melle), and received fertilizer N at an annual rate of 400 kg ha−1. All plots were continuously stocked by beef cattle and stock numbers were adjusted to maintain a constant sward height and to avoid poaching damage. Results for the first 5 years show that the benefits from drainage were modest and, for beef production, unlikely to pay for its costs over the shorter term. The main benefit was in spring when herbage dry matter yield was 11% greater on the drained plots, but with no significant interaction with fertilizer N level or sward type. This benefit was reduced to 3% on an annual basis, due to the effect of the larger soil water deficits sustained by the drained swards in mid-season. Drainage increased the annual liveweight gain per ha by the grazing cattle by 11%. Possible mechanisms accounting for these effects are discussed in relation to the influences of seasonal patterns of weather.

A new model is being developed to study the main elements that affect sustainability within a dairy farm by using multiple goal programming. In this work, we describe the main characteristics of this modelling approach and we evaluate, via optimization, the effect of different dietary strategies and some component attributes such as plant nitrogen (N) uptake and cow N intake on milk and N losses.

The concept of streamss and stream functions are augmented by temporal constraints to provide a framework for the specification of real-time distributed systems. Individual agents, which communicate over the streams, have a relative local clock which may run at a different speed to other local clocks. Compensation functions are used to give a measure of criticality to requirements expressed in the formalism.

About 53 million km2, or 40% of the Earth’s land surface is grassland, containing about one-third of the global stock of terrestrial C. Grasslands are ecosystems where the dominant vegetation component is comprised of herbaceous species, with less than 10% tree cover (Jones and Donnelly 2004). Grasslands are either natural vegetation (e.g. the steppes of central Asia and prairies of North America) or anthropogenic in origin (e.g. north-western and central Europe, New Zealand, parts of North and South America and Australia). Grasslands are heavily relied upon for food and forage production, and about one-third of world milk and beef production occurs on grassland managed solely for these purposes (Conant et al. 2001).

Re-packed soil columns of the Crediton series were sown with white clover or perennial ryegrass, with nitrate managed according to organic and conventional farming regimes respectively. Visual observations revealed a rapid enhancement in soil structure beneath white clover compared to ryegrass and unplanted soil. Enhanced structural differentiation beneath white clover was supported by greater permeability to air and freer drainage to water. Differences in soil structure were verified by water retention measurements over a range of tensions between the wilting and gravity drainage points. The void structure was simulated with the Pore-Cor network model, which verified larger pores beneath clover, a difference in local structuring and a saturated hydraulic conductivity which was four times greater than ryegrass. The study highlighted inadequacies in current approaches to the measurement and interpretation of water retention.

Sustainable catchment management requires increased levels of integration between groups of natural and social scientists, land and water users, land and water managers, planners and policy makers across spatial scales. Multiple policy drivers, covering urban and rural communities and their relationships with land and water use, have resulted in the need for an integrated decision making framework that operates from the strategic national scale to the local catchment scale. Large gaps in integration between policies are resulting in uncertain outcomes of conflicting and competing policy measures. The need for further integration is illustrated by little or no reductions in nitrate and phosphate levels in surface and ground waters in England and Wales. There is a requirement for natural scientists to consider the socio-economic setting and implications of their research. Moreover, catchment system level science requires natural and social scientists to work more closely, to provide robust analysis of the state of the environment that fully considers the bio-physical, social, political and economic settings. The combined use of spatial technologies, scenarios, indicators and multicriteria analysis are increasingly being used to enable improved integration for sustainable catchment management.

Perennial ryegrass and perennial ryegrass/white clover permanent dairy pastures are compared with respect to productivity, environmental impact and financial costs in nitrate vulnerable zones (NVZ) in the UK. With appropriate management, and utilisation of recommended perennial ryegrass and white clover cultivars, white clover is likely to stabilise at around 20% of total dry matter production in a mixed pasture. Plant dry matter production and milk production from a perennial ryegrass/white clover pasture are likely to be similar to that from a perennial ryegrass pasture receiving 200 kg N ha -1 annum -1 and around 70% of that obtained with perennial ryegrass supplied with 350-400 kg N ha -1 annum -1 . Nitrate, phosphorus and methane losses from the system and decreases in biodiversity relative to a grazed indigenous sward are likely to be similar for a perennial ryegrass/white clover pasture and a perennial ryegrass pasture receiving 200 kg N ha -1 annum -1 : nitrate leachate from both systems is likely to comply with European legislation. Greenhouse gas emissions resulting from nitrogen (N) fertiliser production would be avoided with the perennial ryegrass/white clover pasture. Within NVZ stocking rate restrictions, white clover can provide the N required by a pasture at a lower financial cost than that incurred by the application of N fertiliser.

The effective management of acne remains a challenge; achieving an optimal response whilst minimizing adverse events is often difficult. The rise in antibiotic resistance threatens to reduce the future usefulness of the current mainstay of therapy. The need for alternative therapies remains important. Phototherapy has previously been shown to be effective in acne, with renewed interest as both endogenous and exogenous photodynamic therapies are demonstrated for this condition.To determine the effect of narrowband blue light in the reduction of inflammatory and non-inflammatory lesions in patients with mild to moderate acne and to evaluate patient tolerance of the therapy.We performed an open study utilizing a blue LED light source in 30 subjects with mild to moderate facial acne. Two weeks after screening, lesions were counted and recorded by lesion type. Over 4 weeks, patients received eight 10- or 20-minute light treatments, peak wavelength 409-419 nm at 40 mW/cm2. Assessments were taken at weeks 5, 8 and 12 and lesion counts were recorded. Repeated measures-ANOVA and Dunnett's tests, respectively, allowed assessment of the different scores over time and permitted comparison of mean counts.An overall effect on inflammatory counts was observed at week 5, and a statistically significant decrease in inflamed counts was detected at the week 8 assessments, which continued to week 12. There was little effect on non-inflamed lesions. The treatment was well tolerated with adverse events experienced generally rated as being mild and usually self-limiting.Eight 10- or 20-minute treatments over 4 weeks with a narrowband blue light was found to be effective in reducing the number of inflamed lesions in subjects with mild to moderate acne. The treatment had little effect on the number of comedones. The onset of the effect was observable at the first assessment, at week 5, and maximal between weeks 8 and 12. Blue light phototherapy using a narrowband LED light source appears to be a safe and effective additional therapy for mild to moderate acne.

To investigate the effects of plant species in grassland on methane (CH4) and nitrous oxide (N2O) fluxes from soil, fluxes from an orchardgrass (Dactylis glomerata L.) grassland, white clover (Trifolium repens L.) grassland and orchardgrass/white clover mixed grassland were measured weekly from April 2001 to March 2002 using a vented closed chamber method. Related environmental parameters (soil inorganic N content, soil pH (H2O) value, soil moisture content, soil temperature, grass yield, and the number of soil microorganisms) were also regularly monitored. On an annual basis, CH4 consumption in the soil of the orchardgrass grassland, white clover grassland and orchardgrass/white clover mixed grassland was 1.8, 2.4, and 1.8 kg C ha−1 year−1, respectively. The soil bulk density of the white clover grassland was lower than that of the other grasslands. Fluxes of CH4 were positively correlated with the soil moisture content. White clover increased the CH4 consumption by improving soil aeration. Nitrogen supp...