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Until recently, agricultural production was optimised almost exclusively for profit but now farming is under pressure to meet environmental targets. A method is presented and applied for optimising the sustainability of agricultural production systems in terms of both economics and the environment. Components of the agricultural production chain are analysed using environmental life-cycle assessment (LCA) and a financial value attributed to the resources consumed and burden imposed on the environment by agriculture, as well as to the products. The sum of the outputs is weighed against the inputs and the system considered sustainable if the value of the outputs exceeds those of the inputs. If this ratio is plotted against the sum of inputs for all levels of input, a diminishing returns curve should result and the optimum level of sustainability is located at the maximum of the curve. Data were taken from standard economic almanacs and from published LCA reports on the extent of consumption and environmental burdens resulting from farming in the UK. Land-use is valued using the concept of ecosystem services. Our analysis suggests that agricultural systems are sustainable at rates of production close to current levels practiced in the UK. Extensification of farming, which is thought to favour non-food ecosystem services, requires more land to produce the same amount of food. The loss of ecosystem services hitherto provided by natural land brought into production is greater than that which can be provided by land now under extensive farming. This loss of ecosystem service is large in comparison to the benefit of a reduction in emission of nutrients and pesticides. However, food production is essential, so the coupling of subsidies that represent a relatively large component of the economic output in EU farming, with measures to reduce pollution are well-aimed. Measures to ensure that as little extra land is brought into production as possible or that marginal land is allowed to revert to nature would seem to be equally well-aimed, even if this required more intensive use of productive areas. We conclude that current arable farming in the EU is sustainable with either realistic prices for products or some degree of subsidy and that productivity per unit area of land and greenhouse gas emission (subsuming primary energy consumption) are the most important pressures on the sustainability of farming.

Three methods of predicting slurry production were compared with the volumes actually produced on a 150 sow breeding and fattening pig unit. The methods were based on (a) feed, water and slurry relationships measured in crated and penned pigs; (b) values given in the literature and used by ADAS to predict slurry outputs from pigs; (c) a method based on the digestibility of feed and of water measured at the actual piggery. Method (a) was not found appropriate because of the high overall water:meal ratio found in the unit (13:1). Method (b) was able to predict dry matter production accurately but underestimated the volume produced unless the ADAS allowance of 0·5 litres pig −1 day −1 for washing water and leaking drinkers was increased to 10 litres. Method (c) was the best method for estimating volume but underestimated dry matter production. Combining the better aspects of methods (b) and (c) allows volume, dry matter production and dry matter concentration to be predicted satisfactorily. The daily movements of slurry from the reception pit were very variable. The use of water meters on pig units is recommended to identify wastage.

Storage of cattle slurry is a significant source of ammonia (NH3) emissions. Emissions can be reduced by covering slurry stores, but this can incur significant costs, as well as practical and technical difficulties. In this pilot-scale study, slurry was stored in small tanks (500 L) and the effectiveness of natural crust development for reducing NH3 emissions was assessed in a series of experiments. Also, factors important in crust development were investigated. Measurements were made of crust thickness and specially adapted tank lids were used to measure NH3 emissions. Slurry dry matter (DM) content was the most important factor influencing crust formation, with no crust formation on slurries with a DM content of

Three cylindrical reactors, each with a working capacity of approximately 200 litres, were used to investigate composting. The process was optimised and conditions were controlled so that composting on a laboratory-scale thermally resembled that occurring in the core of large open heaps. A baseline flow of humidified air aerated the reactors in five-minute bursts. The reactors operated as closed systems with facilities to analyse the composition of the off-gas for ammonia, oxygen and carbon dioxide. Temperature was used to monitor the progress of the process. Heat loss from the reactor surface was compensated for with an external heat source. A basic model of radial conductive heat losses showed that 53 watts per square-metre would be the maximum heat flux needed to keep the temperature difference across the reactor to within a degree when running at 60 degrees C. A heating cable was used, which could supply 150 watts per square-metre, and the radial temperature difference was reduced to within a degree in more than 60% of the recorded temperatures in the case studies presented. The temperature of the composting material was held at 60 degrees C using a high flow rate 'cooling' aeration with temperature feedback. This, however, led to a mean vertical temperature difference of at least 10 degrees C. The aeration strategy resulted in a well-aerated material, which favoured aerobic microbial activity and the temperature increased as a result of the internally generated heat associated with composting. Three-quarters of the ammonia was emitted in the first week.

Whole piggery slurry and a liquor obtained by mechanical separation were gradually accumulated and stored; changes relating to pollution potential and manurial value were examined. Organic matter was solubilised causing raised soluble-chemical and 5-day biochemical oxygen demands, so increasing soil pollution hazards. These changes were greater in separated liquor than in whole slurry. Odour offensiveness increased, as did malodorous compounds including phenol, p -cresol, skatole and volatile fatty acids (VFA). Manurial value based on N, P and K analysis changed little, but increased VFA and soluble oxygen demand could reduce soil fertility.

Close, largely linear, relationships were found between volatile fatty acids (VFA) determined by gas chromatography, total organic acids (TOA) determined colorimetrically, biochemical oxygen demand (BOD5) and chemical oxygen demand (COD) in the soluble fraction of piggery slurries. Samples were taken from untreated and aerobically-treated slurries. All correlations were significant at P=0.001, with values of r ranging between 0.88 for the correlation of VFA and COD, to 0.97 for the correlation of TOA and BOD5. VFA accounted for up to 69% of BOD5 and 55% of COD. It is suggested that organic acids could replace soluble BOD5 in some situations, since the correlations were good. Prediction of COD from organic acids, or BOD5 from COD, were less accurate, particularly when concentrations were low, since COD contains a biologically inert fraction, which varies with storage. Soluble organic nitrogen was not useful in predicting BOD5 or COD, correlating only at P=0.02.

Odour nuisance arising from piggery slurry can be prevented by aeration. The stability of aerobically treated slurry, which is free of offensive odours, increases as the dry matter of the slurry decreases. This paper investigates the performance of a decanting centrifuge as one means of achieving a lower dry matter in piggery slurry. Slurry was centrifuged to show the effects of various operating conditions; 61% of the total solids were removed from slurry of 8% dry matter content wet basis (d.m.) in the form of fibrous solids of 27% d.m. and 43% of the total solids were removed from slurry of 2% d.m. as fibrous solids of 30% d.m. When the raw slurry had 8% d.m., centrifuging reduced the volume needed for liquid storage by 17%. A particle size analysis of the solids which remained in the centrifuged liquid showed that 98% were less than 0·020 mm diameter. This agrees with the predicted maximum size of particle left in the centrifuged liquid. Centrifuged liquid from the dilute slurry contained only 4% of particles greater than the predicted maximum diameter of 0·012 mm.

The effect of mean micro-organism residence time in the aeration vessel of a continuous culture system for the treatment of whole slurries of excreta from beef cattle and laying hens is compared with its effect on the treatment of piggery waste and to model developed earlier to describe the aerobic treatment of piggery waste and to produce correlating equations to define the quality of treated slurry is considered in relation to cattle and poultry waste treatment.

Effective aerobic treatment of piggery slurry was achieved in a continuous farm scale process sited at a small piggery (2000 pigs). The plant design and the operating conditions were based on data obtained from pilot-scale studies with the aim of preventing or reducing odours from pig slurry at a minimum cost. Raw slurry was separated before passing into the main treatment vessel. Aeration was achieved by recirculating of slurry (achieving jet mixing of the tank contents) through a venturi where air was entrained. Aeration was controlled to maintain redox potential between 100 and 200 mV E h . Slurry was added and withdrawn at hourly intervals, to provide nominal residence times of 1, 2 and 4 days. The performance of the aerobic treatment process in terms of COD reduction could be predicted using data from laboratory and pilot-scale experiments. Some allowance could be made for minor feed fluctuations but a more comprehensive model will be necessary for predictions where larger variations occur in operating conditions. Assessments were made of odour quality using dynamic dilution olfactometers for odour strength, and volatile fatty acids (VFA) concentration as an indicator of odour offensiveness. Results indicate that pilot-scale experiments may overestimate by 10–20% what can be achieved with the farm-scale plant. Nitrogen losses were greatest in the 4-day residence time trial with 56% lost in the form of N 2 gas following a nitrification/denitrification process. Conversely, in the short residence time trials, virtually all of the nitrogen was conserved.

A type of controllable non-point source of gaseous NH3 has been developed, which is simpler, more reliable and more versatile in use than earlier types of source. The source is based on a suitable length of a suitable type of permeable plastic tubing, to which pure NH3 gas is supplied at a suitable pressure. Once steady state is achieved, the emission rate of NH3 from the tubing equals the permeation rate through the tubing wall: the rate is continuously monitored via the rate of weight loss from the cylinder supplying the NH3 gas, mounted on a suitable recording electronic balance. A simple apparatus is described for determining permeation rates of NH3 through samples of different types of tubing, as are two examples of applying the source in field experiments. In the first example, a two-dimensional source was constructed inside the bottom of a clean, dry above-ground cylindrical slurry store (6 m diameter) and used to test passive ammonia flux samplers as a means of measuring NH3 emission rates from su...

In Europe, new legislation on environmental protection requires reductions in emissions of ammonia and odour from animal production. Animal housing is identified as one of the biggest ammonia emission sources in pig production, but abatement techniques for animal houses often require high initial cost. The aims of this study were to investigate the use of layers of oil and foam on slurry under slats. It was found that relatively low-cost, used frying oil (mainly rapeseed oil) could reduce ammonia and odour emissions by about 50% in weaner accommodation. The cost for this technique was Pound Sterling 2.60 per pig place per year. Foam showed poor ammonia abatement potential. The oil was biodegradable, so increasing methane emissions from stored pig slurry by about 60%.

Research on the incidence and effectiveness of natural crusting on slurry storage as a means of ammonia emission abatement was undertaken in studies at farm-scale, pilot-scale and on a small-scale. At the farm-scale, slurry crusting was found to be commonplace across a large proportion (ca 80%) of slurry storage facilities, despite the fact that regular store mixing and agitation was found to be carried out on 68% of farms. Observations provided information on the impact of a range of factors on the potential for crust formation. The most important factors were slurry solids content (crusting increasing with dry matter (DM) content), volume:surface area ratio of the storage (influencing nature of the crust and rate of formation), livestock diet (crusting more likely with grass silage), slurry management (agitation). Of particular importance, were weather conditions with evaporation increasing crusts and rainfall having the opposite effect. From measurements at farm- and pilot-scale (i.e. excluding small-scale comparative studies), mean ammonia emissions were 1.07 and 3.42 g m −2 d −1 NH 3 -N, for crusted and non-crusted slurry stores, respectively. Where direct comparisons between crusted and non-crusted slurry were possible, a reduction in NH 3 emission of about 60% was typical during the measurement period. Although the range in emission measurements was large, the results reported here have confirmed the potential for significant abatement under practical farm conditions. Assuming that natural crusting is as effective in reducing emissions as these results suggest, an objective assessment of crust integrity needs to be developed to assist with effective implementation of mitigation policy. A type of ‘crustometer’ could be developed, at least partly based on the falling weight technique described and tested briefly within the field studies. The work has also identified potential for a modelling approach for the prediction of crust development and, hence, likely emission abatement efficiency.