Introduction:Sustainable agriculture

Today, global agriculture feeds a population of approximately 6.4 billion and delivers a wide range of additional services. These range from waste management and water purification through delivery of fuel, fibre and chemical products to recreation and the conservation of biodiversity. Significant elements of global tourism depend upon ‘sympathetic’ management of farmland. On the positive side, food production has kept pace with demand and there havebeen improvements in safety and reliability of supply while prices have fallen. On the negative side, the global population still experiences major inequalities inproduction, distribution and consumption while the environmental footprint of agriculture is increasingly recognized as a threat to our planet’s capacity toprovide vital ecosystem services. Over recent years, the concept of ‘sustainability’ has emerged and this has been a driver for the development of technologies, practices, products and processes that can maintain the required level of output in a way that compromises future capacity as little as possible. It is recognized that sustainability is a term that requires qualification and is highly case-sensitive. However, there is little doubt that increasing attention is being paid to the development of agricultural systems that seek to ‘rebalance’ the positives and negatives of farming and to do what is feasible to protect for the long-term future, the production capacity and ecological well being of the land.These two special issues of Phil. Trans. R. Soc. B seek to address in detail the approaches that are being adopted to make agriculture more sustainable and toconsider those in a regional context as well as through the contribution that individual components can make to whole systems. We have been fortunate inbeing able to draw on an international team of specialists who have produced a range of critical reviews that consider both past progress and future challenges. The reviews cover successively the context for the debate, the detailed science behind twentyfirst century agricultural development and distinctive regional differences in agricultural systems. This first issue begins with four reviews that consider aspects of sustainability as they apply to global agriculture (Hazell & Wood 2008; Kitzes et al. 2008; Pretty 2008; Scherr & McNeely 2008). There are then papers dealing with whole agricultural systems (Day et al. 2008; Hobbs et al. 2008; Wilkins 2008) followed by more detailed reviews of some of thetechnological approaches that will be needed if sustainability is to be improved (Collard & Mackill 2008; Dennis et al. 2008; Flint & Woolliams 2008; Goulding et al. 2008; Hassanali et al. 2008; Morison et al. 2008; Moss 2008; Smith et al. 2008).We believe that publication of these reviews is particularly timely. Pressure on land, both nationally and globally, will increase for at least the next half century. Despite rapid shifts in human fertility patterns, population growth will result in the world population rising by at least another 2 billion to a maximum of 8.5–9 billion by 2045–2050. Projections of climate change impacts suggest that there will be significant negative impacts on crop and animal production, particularly in the subtropics and tropics. At the same time, demand for animal products indeveloping countries is growing so fast that an extra 300 Mt of grain will be needed by 2050 to meet this need alone. Urban and industrial water use is reducing water availability for agriculture in many regions, and harvesting solar energy for biofuels and industrial feedstocks will further reduce land available for food production. In our view, this means that agriculture in the twenty-first century will have to be very different from agriculture in the twentieth century and this, in turn, will require a radical approach to the investment in and application of research. The reviews in this special issue provide an excellent benchmark by which to measure future progress and valuable visions of howthat future might be achieved. Unless we look anew at agriculture in terms of the balances between wider benefits and impacts and link this to current and futuresocietal drivers, we will continue to pay lip service to the concept of sustainability without ever developing ways to achieve it. We expect that these reviews willcontribute to and move forward this important debate. Additional publication costs for this special issue have been met by financial sponsorship fromthe Lawes AgriculturalTrust, the Stapledon Trust and the John Innes Foundation, all of which are charities dedicated to the conduct and communication of scientific research in support of sustainable agriculture internationally. Financial sponsorship was also received from the Lord Milford fund at IGER and from Defra. Sponsorship was only obtained after completion of the editorial process and acceptance by the journal of the submitted papers.IMPF: 05.5