No abstract

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.

The aim of this study was to apply the life cycle assessment (LCA) method, from cradle to gate, to quantify the environmental burdens per 1,000 kg of expected edible carcass weight in the 3 main broiler production systems in the United Kingdom: 1) standard indoor, 2) free range, and 3) organic, and to identify the main components of these burdens. The LCA method evaluates production systems logically to account for all inputs and outputs that cross a specified system boundary, and it relates these to the useful outputs. The analysis was based on an approach that applied a structural model for the UK broiler industry and mechanistic submodels for animal performance, crop production, and major nutrient flows. Simplified baseline feeds representative of those used by the UK broiler industry were used. Typical UK figures for performance and mortality of birds and farm energy and material use were applied. Monte Carlo simulations were used to quantify the uncertainties in the outputs. The length of the production cycle was longer for free-range and organic systems compared with that of the standard indoor system, and as a result, the feed consumption and manure production per bird were higher in the free-range and organic systems. These differences had a major effect on the differences in environmental burdens between the systems. Feed production, processing, and transport resulted in greater overall environmental impacts than any other components of broiler production; for example, 65 to 81% of the primary energy use and 71 to 72% of the global warming potential of the system were due to these burdens. Farm gas and oil use had the second highest impact in primary energy use (12-25%) followed by farm electricity use. The direct use of gas, oil, and electricity were generally lower in free-range and organic systems compared with their use in the standard indoor system. Manure was the main component of acidification potential and also had a relatively high 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.

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.

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