Sustainable agriculture Are fertilisers necessary for a sustainable nutrient supply? The 33rd Francis New Memorial Lecture

The global population has now exceeded 8 billion and continues to increase; current estimates are that it will reach 9.4-10.1 billion by 2050. It is estimated that more than 460 million people are still unable to find enough food to live a healthy life. The United Nations has therefore set as its Sustainable Development Goal No. 2 to ‘…end hunger, achieve food security and improved nutrition, and promote sustainable agriculture.’ Can this be achieved in a sustainable way without fertilisers? This paper considers the importance of and need for fertilisers in delivering the nutrients essential for long-term sustainable agriculture, reviewing soil nutrient and pH levels and nutrient balances in the UK, Europe and beyond. Between 13 and 20 essential plant nutrients have been identified. Soils can supply many if not all of these, depending on soil composition, but for the macronutrients at least, not in the quantities that modern high-yielding varieties need. This has resulted in very large inputs of fertilisers, especially nitrogen (N): it has been estimated that, in 2008, N fertilisers were responsible for feeding 48% of the world’s population. However, the sometimes inefficient use of fertilisers, especially N and phosphate (P), has resulted in a very large surplus of reactive N (Nr) and P on Earth. Amounts of Nr in soils, water and air are currently estimated as being four times the safe limit, so policy makers and farmers are looking for alternatives to fertilisers, especially N fertiliser. However alternatives to fertiliser N, especially the greater use of biological N fixation, would require major changes in farming, diet and the entire food chain. The likely lower yields risk exporting environmental damage from developed to developing countries, resulting in further degeneration in vulnerable regions of the Global South. It is difficult to see how a sustainable food supply can be achieved without fertilisers when the growing world population demands more and better food. A sustainable agriculture is likely to be dependent on the continued but more efficient use of fertilisers, alongside the recycling of manures and other recyclable materials, with continuously improving good agronomic practices for all nutrients, not just NPK.