Christine Watson, John Baddeley, Tony Edwards & Robin Walker
Crop & Soil Systems Research Group, SAC

Agricultural activities account for a substantial and growing share of the Earth’s land area. The need to provide food, clean water and other ecosystem services to a growing world population while minimizing adverse environmental impacts and use of non-renewable resources is a challenge which requires increasing attention. Nutrient management is pivotal in agriculture because it plays a key role both in food production and in the prevention of soil, water and air pollution.
This presentation will explore how nutrient management affects both production and greenhouse gas emissions from soil. It will draw on long-term grassland and rotational experiments established in Scotland over the last century. These experiments have investigated various combinations of fertilizer applications, liming regimes, cropping systems and practices. The longest running experiment (established 1922) is a six year ley/arable rotation trial with six N, P and K fertility combination treatments which continues with the cropping cycle unchanged. Crop yields have generally increased over the 90 years of the trial, due to the fertilizer treatments but also to changes in agronomic management such as variety. In the treatment which received only farmyard manure, spring oat yields have increased three-fold whereas the treatment that received N, P, K fertilizers and farmyard manure has doubled. Soil organic matter pools differ significantly between fertilizer treatments. 
Results will also be presented from experiments where production relies on nitrogen fixation from forage and grain legumes rather than nitrogen fertilizer. This experiment initiated in 1991 compares two six-year rotations. The first rotation comprises three years of grazed grass-clover leys followed by three years of arable cropping. The second rotation is an arable system with one year grass / red clover (cut and mulched), potatoes, spring wheat, spring beans, spring barley and spring oats. Data emerging from this trial and other associated experiments shows that legume varietal selection can be important in managing nitrous oxide losses.
Our research is focused on providing information which can guide farmers and policy makers in making decisions on future practices. Our experiments are managed with inputs from farmers and advisors.
Acknowledgements: Our research is sponsored by the Scottish Government, Defra and The EU Legume Futures project.