In 2018, agriculture accounted for 18% of Scotland’s total greenhouse gas emissions (GHG), with a significant share coming from nitrogen fertilisers. One policy approach identified as having potential to reduce nitrogen fertiliser use is through leguminous crops to fix atmospheric nitrogen.
This study assesses the opportunities, challenges and barriers influencing potential production of grain and forage legumes in Scotland. Grain legumes are crops such as beans and peas while forage legumes include lucerne (also known as alfalfa), clover and vetch.
We assess the climate mitigation potential of legumes within arable and grassland rotations and comment on the potential to reduce reliance on imported protein.
Current production and trends
- There has been a historical decline in the grain legume area in the EU, largely as a result of economic forces. This is matched in Scotland - there is a low level of production (2.3% of the tillage crop area in Scotland).
- Use of legumes within forage grazing is an accepted practice in Scotland and large areas of improved grassland benefit from their inclusion. There is little scope for an expansion in the area of legumes in pasture.
Availability of land
- There is a large area of land which is theoretically suitable for legume crops growth. Generally, the most suitable land lies in the east of Scotland and the lowlands. However, Scotland’s climate can pose issues for cultivation, leading to a perception among some farmers of poor crop performance.
- Climate change is not expected to have a major effect on the area of land that can support legume crops in Scotland.
- The main way to reduce GHG emissions is through crop substitution, increasing the use of leguminous crops. This results in changes in nitrous oxide emission from soil (through changes in nitrogen fertiliser use and crop residue returns to the soil); and lower emissions from manufacture of nitrogen fertiliser (occurring outwith Scotland).
- Including legumes in crop rotation, one year in five, could lead to an annualised nitrogen saving of 30.8 kg/ha. This is a saving of 24.1%.
- The savings in GHG emissions from including legumes are 107.4 kt CO2e/yr, rising to 160.8 kt CO2e/yr when fertiliser manufacture GHG emissions (outwith Scotland) are included. This is equivalent to 1.4% of Scotland’s agriculture emissions, rising to 2.2% when fertiliser manufacture GHG emissions are included.
Market and other constraints and opportunities
- The UK is reliant on imports to provide 47% of protein sources used in animal feeds. With greater awareness of the need for sustainable protein, the importance of domestic protein sources is set to increase.
- Economic conditions for both demand and supply are key influences on the area of legumes grown. As an ingredient in animal feed, legumes can be uncompetitive with other protein sources.
- From a grower’s perspective, the price paid for legumes is too low and other cropping options give higher and more reliable returns. However, new markets for human food ingredients and a growing demand in the fish feed sector could offer opportunities.
- There are a range of technical and logistical limitations which depress the market for grain legumes. These may require some intervention but should not be significant, long-term barriers.
- Perceived poor performance of grain legumes in Scotland has suppressed the area cropped. However, greater awareness amongst the industry of the potential of legumes to support more sustainable rotations and soil health, and to help manage disease and “regenerate” land, are increasing interest.