Spreading the Word on Legumes

Published on 15 July 2011 in Sustainability and Communities

Key Challenges

Optimising soil fertility, particularly by ensuring soils contain the optimum nitrogen levels, is a vital component of any farming system. The two main approaches are the use of chemical fertilisers and biological nitrogen fixation (BNF) through legume use. Fertilisers are costly and energy expensive. In contrast, BNF is relatively cheap but is more difficult to manage consistently due to variable nitrogen fixation and availability to crops. Beyond improving soil fertility, legumes can bring benefits to soil structure and weed, pest and disease control but achieving this poses additional challenges.

Key Benefits

The role leguminous crops can play in contributing to reducing energy use, the environmental burden of cropping systems and food security is gaining momentum. SRUC has been developing practical approaches to improve the integration of BNF into agricultural systems. Research is focused on how legumes can:

• offer a partial replacement to chemical fertilisers
• help improve the environmental impact of farming systems
• help reduce farmers’ costs
• improve soil structure
• reduced weeds, pests and diseases

SRUC’s ongoing Scottish Government-funded research aims to improve the quantification of these benefits.

All organic farms use legume based systems. While many mixed farms have a legume component, such as in their grassland, synthetic nitrogen is frequently used on conventional farms. Estimates of the amount of nitrogen legumes can contribute to soil vary widely, from 20 to 500kg of nitrogen per hectare each year. However, based on current ammonium nitrate prices of around £300 per tonne, if even half of the existing Scottish area of crop and grassland could provide the modest amount of 20 kg of nitrogen a year through BNF, the annual Scottish nitrogen fertiliser bill could be reduced by at least £15 million.

SRUC’s research and associated advisory services on range of benefits of legume rotations has historically concentrated on their use in organic farms, but advice is increasingly being delivered to a broader range of farmers. Over the last 10 years, as part of the Scottish Government’s Organic AA311 programme, more 10,000 people have attended over 300 meetings, workshops, open days and training events. More than 12,000 telephone enquiries have been received and almost 300 articles have been published on various organic topics.

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