A win-win for legume mixtures

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A win-win for legume mixtures

A win-win forlegume mixturesA countrywide research project demonstrates how the productivity of fertilitybuilding leys can be increased with a diverse range of legume and grass speciesThe inter-relationship between food production andbiodiversity is now well established. The ecosystemservices provided by the organisms within theenvironment include, for example, nutrient cycling, pestregulation and pollination, to name but a few. However,perhaps the greatest challenge now facing agriculturalproduction is to find ways of enhancing these ecosystemservices, while at the same time increasing food production– particularly in light of food security issues.A range of farm and landscape management optionsinclude ‘setting aside’ land for wildlife. However, someproponents argue that such land should be used for foodproduction. While the debate continues, there is no doubtthat a large body of scientific evidence from the last threedecades highlights the wildlife benefits of organic farming.This article will describe how the Legume LINK project hasidentified a win-win system for biodiversity conservationand increased productivity through legume-base fertilitybuilding. Although this project has focused on organicfarming systems, it is of direct relevance to non-organicproduction, particularly with the increasing interest inlegumes across the industry.Beyond grass clover leysCurrent organic rotations rely predominantly on red andwhite clover leys fertility building, usually mixed withryegrasses. While these leys have a significant potentialfor nitrogen fixation under optimal conditions, theestablishment of simple grass clover leys can be risky underdry conditions. The idea of adding more legume specieswith different tolerances to environmental factors such asdrought, water logging and acidity therefore promises toincrease the reliability of ley establishment.At the same time, some landmark studies in ecologicalresearch show that increasing the species diversity ingrasslands tends to increase overall grassland productivity,because the different plant species complement eachother. Together, the mixed species make better use of theavailable resources such as water, light or nutrients. But canthis principle be applied to agricultural production systems?On-farm trialsTo test the potential of using diverse mixtures in the ley weassessed the performance of a highly diverse ley mixtureon a large number of farms throughout the UK. Theseon-farm trials are part of the Defra-funded Legume LINKproject (see right). Here we report the results from 12organic farms and one non-organic farm in the south andeast of England.The tested mixture, called the All Species Mix, composedof 10 legume species and four grass species (see Table,opposite). In 2009, the mix was sown on each farm in a0.5ha strip alongside a control ley. The species compositionof the control ley was chosen by the participating farmer.Both the All Species Mix and the control ley were sownat the same time and treated equally throughout the trialperiod. On some of the farms the leys were grazed bysheep or cattle; on others the leys were only cut.FIND OUT MOREThe project is led by theOrganic Research Centreand aims to improvefertility building usinggreen manures. Researchpartners are Duchy College,IBERS Aberystwyth, TheArable Group, RothamstedResearch, and the ScottishAgricultural College.Industry partners are AbacusOrganic Services, HGCA,the Institute for OrganicTraining and Advice, OrganicFarmers & Growers, theOrganic Seed Producers, theScottish Organic ProducersAssociation and the SoilAssociation. The project isfunded by Defra throughthe Sustainable ArableLINK programme andindustry partners. Thanks toparticipating producers andfunding from BBSRC LINKfor Rob Brown’s PhD project.40 Organic Farming Winter 2011


Throughout the trial period we repeatedly assessedthe presence and cover of the various sown plantspecies and weeds. In spring 2011, we took samplesof both the All Species Mix and the control ley todetermine its productivity, measured as dry matter (DM)yield on four sample quadrats per ley. Results fromthese field experiments reveal that, in the second yearof the ley (2010), the number of crop species found inthe mix was on average twice as large as the controlley (10 vs. 5). At the same time, the total DM yieldin 2011 was 22% higher in the mixture than in thefarmer-chosen control ley. The results show that theAll Species Mixture was not only more diverse but alsomore productive than the control leys. As research atRothamsted Research within the Legume LINK projectshows, this increase in DM biomass of the ley is likelyto be translated into higher yields of a following wintercereal.BACK TO BASICSRob Brown, Oliver CrowleyLegume and grass species included inthe All Species Mixture of Legume LINKGroupCloverOther legumesGrassesSpeciesAlsike cloverCrimson cloverRed cloverWhite cloverBirdsfoot trefoilBlack medicLarge birdsfoot trefoilLucerneMeadow peaSainfoinItalian ryegrassMeadow fescuePerennial ryegrassTimothyOPPOSITE: Birdsfoot trefoilTOP: Lucerne ABOVE:Crimson cloverMore benefitsAn ongoing PhD project at the University of Readingfurther indicates that the higher diversity in the AllSpecies Mixture supports more wildlife than simplerleys. In particular, growing legume species together thathave different flowering times extends the availabilityof nectar for key pollinator species such as bumblebees.For example, including early flowering species such ascrimson clover helps pollinators establish their coloniesin the critical early spring phase.Multi-species leys offer even more potentialadvantages. Once the ley is incorporated into the soil,the residues of the legumes and grasses break downand release nitrogen which can be taken up by thefollowing crop. Normally, the timing of the nitrogenrelease from the ley residues does not perfectly matchthe nitrogen demand by the following crop, with theconsequent risk of nutrient loss either through leachingor in gaseous form. However, a mixture of species thathave different decomposition rates means the release ofnitrogen can be spread out over time, which potentiallyallows a higher proportion of nitrogen to be taken upby the following crop.Plant decomposition rates depend, for example,on lignin and phenolic contents. Mixing species withdifferent lignin and phenolic profiles may thereforeprovide opportunities for improving the synchronybetween nitrogen release and demand. The variouslegume species trialled in the Legume LINK project arecurrently being analysed for the chemical compositionof their above and below-ground residues. Results willthen be used to put together tailored species mixtureswith optimal decomposition properties.The research concludes that both productivity andthe diversity in the farmed landscape can be increasedby including species-rich legume-based leys in therotation. Look out for a second article from the LegumeLINK project in the next issue of Organic Farming.Thomas Döring, Oliver Crowley, Helen Pearce (OrganicResearch Centre), Jon Storkey (Rothamsted Research),Rob Brown and Hannah Jones (University of Reading)41 Organic Farming Winter 2011

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