Biodiversity plays a crucial role in maintaining healthy ecosystems and within agricultural landscapes, legumes can be powerful in encouraging this. The inclusion of legumes within cropping systems has a distinct ability to improve the biodiversity of farm ecosystems, both spatially and temporally at below and above-ground scales.
The benefits of nitrogen fixation
An immediate positive impact of legumes on biodiversity are the effects of their nitrogen fixation on surrounding soil health; a legumes ability to fixate atmospheric nitrogen provides ideal soil conditions for other plants or organisms, acting as a reliable nitrogen source. For example, nitrogen transfer from clover to wheat is related to increased earthworm presence and activity, which indicates the soil has ideal conditions for biological activity and even microbial activity.
The ability for legumes to fixate their own nitrogen also reduces the dependence on applied nitrogen fertilisers in areas in which legumes are present or have been in the past. Using applied chemical fertilisers can cause eutrophication, which causes excessive plant and algal growth and is detrimental to aquatic ecosystems and their subsequent inhabitants and biodiversity.
Replacing nitrogen fertilisers with self-sufficient nitrogen-fixing legumes allows for the generation of beneficial nitrogen and ammonia within soils, without the risk of chemical fertiliser runoff causing eutrophication which hinders biodiversity.
The attraction of pollinators and inhabitants
Beyond the nutritional benefits on biodiversity, legumes can visually effectuate biodiversity through their attraction of pollinators. A flowering legumes provision of nectar and pollen helps sustain pollinator populations, such as bees and butterflies, which may not have been otherwise present in an area lacking floral resources.
The physical presence of legumes may also provide habitats for other taxa, be it insects or small mammals. For example, lucerne, a leafy legume, act as a significant habitat for grasshoppers. This provision of habitats and their subsequent inhabitants can supply animals that act as prey and provide foraging habitats for larger organisms, like farmland birds, bats and vertebrates.
The benefits of stable soil structures
Legumes can improve soil structure due to their extensive rooting systems that provide an intact soil structure with minimal disturbance, attracting beneficial insects and earthworms to the stable soil. Beyond improving animal diversity, the maintenance of stable topsoil also sustains plant diversity, by providing more structured soils and ideal growing conditions for other plant types or crops. However, the benefits of soil structure go beyond diversity and include improved root water systems and assist with carbon sequestration.
Contributions towards more resilient food chains
The localised benefits of legumes on biodiversity can more largely contribute towards boosting biodiversity within a farm’s wider food chain, as the increased presence and diversity of smaller organisms provide food for larger, more mobile species across the ecosystem. These trophic interactions also contribute towards the transfer of nitrogen-rich substances throughout the food chain and aid even large animals in their survival and access to nutrient-rich prey.
Implementing legumes into grassland systems
The UK Agri-Tech Centre is collaborating with LEAF on the Nitrogen Utilisation Efficiency Legumes (NUE-leg) project, a DEFRA on-farm and research trial looking to eliminate the dependence of UK grassland farming on applied nitrogen fertilisers. It aims to do this by developing solutions to reduce environmental impacts while enhancing the economics and sustainability of grassland farming and promoting on-farm biodiversity.
Incorporating legumes into agricultural practice is not just strategic for improving crop growing conditions, but a vital step towards enhancing and sustaining biodiversity across the entire ecosystem.