Adrian G. Williams

Energy and the food system

Modern agriculture is heavily dependent on fossil resources. Both direct energy use for crop management and indirect energy use for fertilizers, pesticides and machinery production have contributed to the major increases in food production seen since the 1960s. However, the relationship between energy inputs and yields is not linear. Low-energy inputs can lead to lower yields and perversely to higher energy demands per tonne of harvested product. At the other extreme, increasing energy inputs can lead to ever-smaller yield gains. Although fossil fuels remain the dominant source of energy for agriculture, the mix of fuels used differs owing to the different fertilization and cultivation requirements of individual crops. Nitrogen fertilizer production uses large amounts of natural gas and some coal, and can account for more than 50 per cent of total energy use in commercial agriculture. Oil accounts for between 30 and 75 per cent of energy inputs of UK agriculture, depending on the cropping system. While agriculture remains dependent on fossil sources of energy, food prices will couple to fossil energy prices and food production will remain a significant contributor to anthropogenic greenhouse gas emissions. Technological developments, changes in crop management, and renewable energy will all play important roles in increasing the energy efficiency of agriculture and reducing its reliance of fossil resources.

Predicting the environmental impacts of chicken systems in the United Kingdom through a life cycle assessment: Egg production systems

The aim of this study was to apply a life cycle assessment (LCA) method, from cradle to gate, to quantify the environmental burdens per 1,000 kg of eggs produced in the 4 major hen-egg production systems in the United Kingdom: 1) cage, 2) barn, 3) free range, and 4) organic. The analysis was based on an approach that applied a structural model for the industry and mechanistic submodels for animal performance, crop production, and nutrient flows. Baseline feeds representative of those used by the UK egg production industry were used. Typical figures from the UK egg production industry, feed intake, mortality of birds, farm energy, and material use in different systems were applied. Monte Carlo simulations were used to quantify the uncertainties in the outputs and allow for comparisons between the systems. The number of birds required to produce 1,000 kg of eggs was highest in the organic and lowest in the cage system; similarly, the amount of feed consumed per bird was highest in the organic and lowest in the cage system. These general differences in productivity largely affected the differences in the environmental impacts between the systems. Feed production, processing, and transport caused greater impacts compared with those from any other component of production; that is, 54 to 75% of the primary energy use and 64 to 72% of the global warming potential of the systems. Electricity (used mainly for ventilation, automatic feeding, and lighting) had the second greatest impact in primary energy use (16-38%). Gas and oil (used mainly for heating in pullet rearing and incineration of dead layer birds) used 7 to 14% of the total primary energy. Manure had the greatest impact on the acidification and eutrophication potentials of the systems because of ammonia emissions that contributed to both of these potentials and nitrate leaching that only affected eutrophication potential. The LCA method allows for comparisons between systems and for the identification of hotspots of environmental impacts that could be subject to mitigation.

Environmental Benefits of Livestock Manure Management Practices and Technology by Life Cycle Assessment

Abstract An environmental Life Cycle Assessment (LCA) procedure is constructed to compare the total emissions from different techniques for managing livestock wastes. Life Cycle Assessment is a method of holistically and systematically accounting for the environmental benefits and burdens of the production of goods and services including consequential burdens generated elsewhere. As waste emissions are very variable, the methodology is extended to include the uncertainty in the estimates in order to indicate the significance of differences between techniques. The object is to inform policy of whether options are better for the environment by quantifying potential emissions abatement, by highlighting priority environmental impacts and by revealing compromises for further investigation. This paper reports comparative LCAs for several pig waste management options. For example, various slurry application techniques, including: splash plates, band spreaders and injection. If the splash-plate system is taken as a reference, the injector system causes only 64% of the environmental acidification and 71% of the eutrophication of surface waters. The benefits must be offset against the increase in nitrate leaching of 50%. In contrast, the band spreader system offers 28% of the benefits of injection. The environmental impacts have also been expressed as a proportion of the UK national emissions. This gives each impact a weighted-value that enables direct comparisons of disparate impacts. Although band spreader systems showed an aggregated, or total, environmental impact reduction of almost 10%, the reduction is not significant when uncertainty is taken into account. Using an anaerobic digester shows few overall benefits due to the fugitive losses of methane. However, if these can be eliminated the global warming potential from waste management is reduced close to zero.

Storage of piggery slurry

Abstract 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.

Crusting of Stored Dairy Slurry to Abate Ammonia Emissions

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 <1%. Generally, crusts began to form within the first 10 to 20 d of storage, at which time NH3 emission rates would decrease. The formation of a natural crust reduced NH3 emissions by approximately 50%. The type of bedding used in the free stall barn did not influence crust formation, nor did ambient temperature or air-flow rate across the slurry surface. There was a large difference in crust formation between slurries from cattle fed a corn (Zea mays L.) silage-based diet and those fed a grass silage-based diet, although dietary differences were confounded with bedding differences. The inclusion of a corn starch and glucose additive promoted crust formation and reduced NH3 emission. The maintenance of a manageable crust on cattle slurry stores is recommended as a cost-effective means of abating NH3 emissions from this phase of slurry management.

Do foods imported into the UK have a greater environmental impact than the same foods produced within the UK

PurposeThis study of seven foods assessed whether there are modes or locations of production that require significantly fewer inputs, and hence cause less pollution, than others. For example, would increasing imports of field-grown tomatoes from the Mediterranean reduce greenhouse gas (GHG) emissions by reducing the need for production in heated greenhouses in the UK, taking account of the additional transport emissions? Is meat production in the UK less polluting than the import of red meat from the southern hemisphere?MethodsWe carried out a life-cycle inventory for each commodity, which quantified flows relating to life-cycle assessment (LCA) impact categories: primary energy use, acidification, eutrophication, abiotic resource use, pesticide use, land occupation and ozone depletion. The system boundary included all production inputs up to arrival at the retail distribution centre (RDC). The allocation of production burdens for meat products was on the basis of economic value. We evaluated indicator foods from which it is possible to draw parallels for foods whose production follows a similar chain: tomatoes (greenhouse crops), strawberries (field-grown soft fruit), apples (stored for year-round supply or imported during spring and summer), potatoes (early season imports or long-stored UK produce), poultry and beef (imported from countries such as Brazil) and lamb (imported to balance domestic spring–autumn supply).Results and discussionTotal pre-farm gate global warming potential (GWP) of potatoes and beef were less for UK production than for production in the alternative country. Up to delivery to the RDC, total GWP were less for UK potatoes, beef and apples than for production elsewhere. Production of tomatoes and strawberries in Spain, poultry in Brazil and lamb in New Zealand produced less GWP than in the UK despite emissions that took place during transport. For foods produced with only small burdens of GWP, such as apples and strawberries, the burden from transport may be a large proportion of the total. For foods with inherently large GWP per tonne, such as meat products, burdens arising from transport may only be a small proportion of the total.ConclusionsWhen considering the GWP of food production, imports from countries where productivity is greater and/or where refrigerated storage requirement is less will lead to less total GWP than axiomatic preference for local produce. However, prioritising GWP may lead to increases in other environmental burdens, in particular leading to both greater demands on and decreasing quality of water resources.

The energy efficiency of organic agriculture: a review.

Growing populations and a constrained fossil-manufactured energy supply present a major challenge for society and there is a real need to develop forms of agriculture that are less dependent on finite energy sources. It has been suggested that organic agriculture can provide a more energy efficient approach due to its focus on sustainable production methods. This review has investigated the extent to which this is true for a range of farming systems. Data from about 50 studies were reviewed with results suggesting that organic farming performs better than conventional for nearly all crop types when energy use is expressed on a unit of area basis. Results are more variable per unit of product due to the lower yield for most organic crops. For livestock, ruminant production systems tend to be more energy efficient under organic management due to the production of forage in grass–clover leys. Conversely, organic poultry tend to perform worse in terms of energy use as a result of higher feed conversion ratios and mortality rates compared to conventional fully housed or free-range systems. With regard to energy sources, there is some evidence that organic farms use more renewable energy and have less of an impact on natural ecosystems. Human energy requirements on organic farms are also higher as a result of greater system diversity and manual weed control. Overall this review has found that most organic farming systems are more energy efficient than their conventional counterparts, although there are some notable exceptions.

Continuous aerobic treatment of piggery slurry for odour control scaled up to a farm-size unit

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.

An assessment of ways to abate ammonia emissions from UK livestock buildings and waste stores. Part 1: ranking exercise

Abstract The options for abating ammonia emissions from livestock buildings and waste stores under UK conditions have been assessed. There is increasing interest in reducing such emissions, which contribute to long-range atmospheric pollution problems, and which, via subsequent deposition, can also harm sensitive ecosystems. A literature review was first carried out, and a “brainstorm” idea-generating session was held, together leading to lists of feasible abatement approaches: one for each of a range of types of livestock buildings and waste stores. A ranking exercise was then conducted. A set of aspects of each application of each feasible abatement approach was drawn up: the aspects considered included not only capital costs and running costs but also such others as animal welfare, stage of development and knock-on effects. Each aspect of each application of each approach was given a ranking of between 1 (very poor) and 5 (very good). When the aspects of “potential abatement” and “achievable abatement now”, as well as either “capital costs” or “animal welfare”, were weighted by a factor of 5, the “best bet” abatement approaches for livestock buildings were identified as (a) dietary manipulation (for all types), (b) raising the C/N ratio by generous use of bedding (for any buildings based on solid manure), (c) exhaust air cleaning, especially by bioscrubbers (for force-ventilated pig and poultry buildings), (d) oil layers or (e) fixing with acid (for slurry-based piggeries) and (f) drying by ventilation of muck (for any poultry building). For waste stores, the “best bet” abatement approaches were identified as (g) replacing storage with industrial scale processing or (h) with land filling (niche solutions only), (i) dietary manipulation, (j) fixing with acid (slurries only), (k) increasing the surfaces resistance to ammonia volatilisation (by crusts for cattle slurry, but by floating granules for pig slurry), (l) minimising surface area by heap shape (solid manures), and (m) cover sheets (solid manures). For stored poultry manure, the low moisture content allowed good showings by the additional options of (n) drying, and, in the case of poultry manure with litter in certain parts of the UK, (p) sale for combustion in a Non-Fossil Fuel Obligation (NOFFO) power station, the electricity from which commands a higher price than that from a conventional power station. A closer look at the economic consequences of different abatement approaches was taken by means of a mathematical model: this work is reported in a companion paper.

Centrifugation for separating piggery slurry 1. The performance of a decanting centrifuge

Abstract 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.