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The Power of Clover: a win-win for bees, farmers and the environment

Farm Practices
clover
biodiversity
pollination
bees

Research from Ciaran Harris & Francis L.W. Ratnieks, University of Sussex

In recent years, there has been growing recognition of the vital role played by agriculture in supporting the biodiversity of flowering plants and pollinators. It’s also becoming increasingly evident that incorporating flower-rich habitats can bring immense benefits to farmers and the environment as a whole.

Providing flowers for bees in farm landscapes is especially possible in grasslands, which can include flowers such as clover, but also in arable land, with flowering crops such as oilseed rape or short-term clover plantings.

Improved grasslands are the largest type of land use in UK farming, constituting 47% of UK land area. But many are grass monocultures receiving high nitrogen (N) fertiliser inputs that provide very little food for bees. In addition, a wide range of environmental problems can be exacerbated by high N inputs, including water contamination (e.g., nitrate and nitrite have certain maximum permissible levels in drinking water) and eutrophication (e.g., water that encourages excessive algal growth), greenhouse gas emissions, and negative impacts on biodiversity and wildlife.

Encouraging practices which reduce N fertiliser use can have widespread benefits for bees, wildlife and the environment. But how can this be done while maintaining food production and farmer income? 

Clover: a farmer’s friend

Clover, often considered a common weed, is a remarkable plant. Traditionally overlooked and undervalued, this resilient and versatile legume offers a wide range of advantages to both farmers and the environment.

Bees, the tireless pollinators that play a vital role in our food production, greatly benefit from the presence of clover. Its vibrant, nectar-rich flowers provide bees, and other beneficial insects, with a consistent and easily accessible food source. Although white clover was once widely used in UK agriculture for soil fertility building, in the twentieth century much was replaced by N fertiliser, depriving bees of a major food source. In 1952, white clover was the main nectar flow for beekeepers, but by 1993, it was considered less important than other common non-crop countryside plants such as bramble.

Unlike many other flowering plants, clover blooms for an extended period, ensuring bees have a continuous supply of nectar throughout the growing season. This is especially important during times when other flowers may be scarce. Researchers at the University of Bristol showed that by adding red clover to just 1% of farm area the number of bumblebee nests the farmland can support could increase more than twofold[1].

In turn, bees pollinate the clover, contributing to its reproduction and genetic diversity. By supporting pollinator populations, clover indirectly supports the pollination of countless other crops, helping to ensure food security.

For farmers, clover offers an array of advantages. One of the most significant benefits is nitrogen fixation. Clover has the unique ability to convert atmospheric nitrogen into a form that other plants can use. This process, called nitrogen fixation, enriches the soil with essential nutrients, reducing the need for synthetic fertilizers. Clover also provides edible to livestock via grazing or hay/silage.

Farm trials of clover show higher yield, higher soil nitrogen content and fewer emissions

The Laboratory of Apiculture and Social Insects (LASI) at the University of Sussex recently reviewed the wide range of benefits for farmers, the environment, and bees provided by growing clover in agricultural land[2]. Here they share the key points.

Experiments in England and Wales have shown that white clover plus perennial ryegrass swards have similar dry matter and milk yield to grass monocultures fertilised with an additional 200 kg N per ha per year[3].

Other UK field trials have shown that when used as a green manure white and red clover achieve significantly higher subsequent winter wheat yield, dry matter yield and soil N content after one year of green manuring than perennial ryegrass monocultures[4]. Additionally, both red and white clover also increase spring wheat yields after short-term inclusion in cereal rotations or when under sown[5].

Lower N applications resulting from N fixed by clover, reduce N leaching into water and greenhouse gas emissions. Less than 20% of N applied to the land in fertiliser is actually incorporated into agricultural products, with the rest leaching into groundwater, rivers, and lakes as nitrate and nitrite, or the atmosphere as N2 gas or nitrous oxide[6].

Nitrous oxide, N2O, is a potent greenhouse gas. For every 100kg N applied, 10kg of nitrous oxide is emitted[7]. By fixing N in root nodules, and therefore not having N present in a reactive form in the soil, clover can help reduce these emissions. Fossil fuels needed in the manufacture, transport, and application of fertiliser are also a source of CO2. For clover, the energy needed for N fixation comes from the sun via photosynthesis.   

Clover can also improve soil structure in grasslands by increasing earthworm abundance and improved root development. Grass plus clover mixtures can also reduce weed invasion[8].

Which bees benefit from clover?

As honeybees are frequent visitors to white clover, its use may help counteract the decline of managed honeybee colonies in the UK, which have declined by 75% in the last century[9]. Clover- and legume-rich grasslands are also an important food source for bumblebees. Shorter-tongued bumblebee species tend to be more abundant on white clover, whereas longer-tongued species, which are of greater conservation concern in the UK, more frequently visit red clover.

Aside from honeybees and bumblebees, other bee species, of which there are c.240 additional species in Britain, are less frequent visitors to clover and legumes. Moreover, the long corolla tubes of clover flowers make the nectar inaccessible to the mouthparts of most hoverfly species.

A potential solution to this is planting multi-species swards to increase the range of pollinators which benefit. These seed mixes can include additional legumes such as sainfoin, vetches, and birds foot trefoil, and forbs such as chicory. Diverse grassland swards bring a variety of additional benefits including improved livestock performance, stability, drought resistance, and reduced weed invasion.

In the context of the University of Sussex’s research experience, many farmers were not aware that one of the benefits of clover was to bees and insects. Given the high cost of N fertiliser, using clover can be a low-cost way to sustain agricultural productivity, reduce environmental impact, and improve the food supply for bees. Increasing the use of clover can therefore produce a ‘win-win-win’ for farmers, the environment, and bees, and can be an important part of a wider transition towards nature-friendly farming.

 References

  1. Timberlake TP, Vaughan IP, Memmott J (2019) Phenology of farmland floral resources reveals seasonal gaps in nectar availability for bumblebees. J Appl Ecol 56:1585–1596. https:// doi. org/ 10. 1111/ 1365- 2664. 13403

  2. Harris, C., Ratnieks, F.L.W., 2021. Clover in agriculture: combined benefits for bees, environment, and farmer. J. Insect Conserv. 1–19. https://doi.org/10.1007/s10841-021-00358-z

  3. Andrews M, Scholefield D, Abberton MT et al (2007) Use of white clover as an alternative to nitrogen fertiliser for dairy pastures in nitrate vulnerable zones in the UK: productivity, environmental impact and economic considerations. Ann Appl Biol 151:11–23. https:// doi. org/ 10. 1111/j. 1744- 7348. 2007. 00137.x

  4. Stopes C, Millington S, Woodward L (1996) Dry matter and nitrogen accumulation by three leguminous green manure species and the yield of a following wheat crop in an organic production system. Agric Ecosyst Environ 57:189–196. https:// doi. org/ 10. 1016/ 0167- 8809(95) 01002-5

  5. Doel JM (2013) Accumulation and recovery of nitrogen in mixed farming systems using legumes and other fertility-building crops

  6. Jarvis SC (1993) Nitrogen cycling and losses from dairy farms. Soil Use Manag 9:99–104. https:// doi. org/ 10. 1111/j. 1475- 2743. 1993. tb009 37.x

  7. IPCC (2006) 2006 IPCC Guidelines for national greenhouse gas inven- tories, national greenhouse gas inventories programme. https:// www. ipccn ggip. iges. or. jp/ public/ 2006gl/ index. html.

  8. de Haas BR, Hoekstra NJ, van der Schoot JR et al (2019) Combining agro-ecological functions in grass-clover mixtures. AIMS Agric Food 4:547–567. https:// doi. org/ 10. 3934/ agrfood. 2019.3. 547

  9. Balfour, N.J., Ollerton, J., Castellanos, M.C., Ratnieks, F.L.W., 2018. British phenological records indicate high diversity and extinction rates among late-summer-flying pollinators. Biol. Conserv. 222, 278–283. https://doi.org/10.1016/j.biocon.2018.04.028

  10. Neumann P, Carreck NL (2010) Honey bee colony losses. J Apic Res 49:1–6. https:// doi. org/ 10. 3896/ IBRA.1. 49.1. 01