The use of leguminous crops, such as peas, beans and clovers, in farming systems can optimise soil nitrogen levels, improve soil structure and help control weeds, diseases and pests. If even half of Scotland’s area crop and grassland could provide 20 kg of nitrogen a year through the use of legume roations, the annual nitrogen fertiliser bill could be reduced by at least £15 million. Research by SRUC on legume based crop rotations has led to an increased awareness and understanding of their benefits. SRUC’s research has encouraged more farmers to adopt legume based rotations, particularly as nitrogen fertiliser prices remain high.
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.
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.
Research by SRUC on legume based crop rotations has led to an increased understanding of their benefits, which is being passed on to farmers. Over the last 10 years, more 10,000 people have attended over 300 meetings, workshops, open days and training events.
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.
The James Hutton Institute
SRUC Crop Homepage
Nitro Europe and Legume Futures (both EU) as well as LegLINK (Defra LINK) have provided collaboration opportunities since 2006.
The EC, Defra and the Scottish Government RESAS Strategic Research Programme.
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Author: Dr Robin Walker Robin.Walker@sruc.ac.uk