Rotational legume and herb-rich swards

Rotational legume and herb-rich swards

Sowing a diversity of legumes like clover, and herbs such as ribwort plantain alongside grasses in short-term leys for cutting or grazing can provide opportunities for wildlife.

What

Legume and herb-rich swards will have much more benefit to wildlife if plants have the chance to flower, even if only for short periods. This could be through an extended rest period between grazing or leaving small areas uncut in mown fields.

Field margins - Upton Estate (Martin Warren) (9)

Why

Legume and herb rich swards do not have the wildlife conservation value of the wildflowers and grasses that make up unimproved permanent grasslands. However, they offer a productive alternative to reseeds based on simple grass mixes, providing a wider range of food sources for insects, farmland birds and other wildlife than standard temporary leys. Legumes in these swards will be used by long-tongued bees and some solitary bees, while other herbs will provide food for different insects.  Many of these insects are beneficial to farming as they pollinate crops and also help control harmful pests. In turn many of these insects will provide food for birds and bats.

Legumes provide the soil with free nitrogen, typically fixing between 100 and 150 kg N/ ha/year from the atmosphere. Because of this free nitrogen, legume-rich swards can be highly productive with little artificial fertiliser, reducing the financial and environmental costs associated with ‘bagged’ (inorganic) fertiliser.

Given the same growing conditions, swards with a greater range of species yield more than those with  fewer species. Plants vary in how they extract nutrients and intercept light, so mixtures can exploit these resources more efficiently. A wider diversity of plants will also increase resilience to pests, disease and weather extremes. The presence of deeper-rooting plants, such as red clover, chicory and plantains, provides some drought tolerance and helps with maintaining good soil structure.

Legume- and herb-rich mixtures also provide nutritional and health benefits to livestock. They increase the protein and mineral content of the forage and some herbs can provide an increased defence against internal parasites. Legumes and herbs also stay leafy for longer than grasses, so digestibility and palatability do not decline as fast when swards are left to get taller prior to mowing or grazing.

Short-haired bumblebee Bombus subterraneus, close up of individual foraging on a flower

How

It is important that permanent grasslands with a good mix of native grasses and flowers are not destroyed through re-seeding. These should be maintained or restored (see advice on existing habitats). Legume and herb-rich swards are generally sown as temporary grass leys, as the species used (especially agriculturally-bred cultivars) will not persist in the sward for many years. As an introduction, consider sowing as a part-field option alongside a more conventional re-seed, perhaps by sowing a diverse legume/herb mix on a headland next to a water body or other habitat.

There is a wide choice of legumes, herbs and grasses that can be sown, but try to match mixes to your local conditions and the desired use as plants vary in their requirements, resilience and flexibility of use.

Legumes

Likely to be based on red clover and white clover, but a range of legumes are available: red clover, white clover, bird's-foot trefoil, yellow trefoil, meadow vetchling, alsike clover, lucerne and sainfoin (calcareous soils).

Herbs

Chicory, ribwort plantain and yarrow have some proven agricultural benefits. Many others are available that benefit wildlife e.g. forage burnet, common sorrel, self-heal, black knapweed, oxeye daisy and lady’s bedstraw, but there is limited information on their agricultural value.

Grasses

Ryegrass dominates modern grass mixes, but many other grasses are equally productive at moderate nitrogen input levels (such as the amounts fixed by legumes) eg timothy, cocksfoot and meadow fescue. Highly competitive grasses can out-compete legumes and herbs during establishment.

To establish, shallow sow on to a clean, fine, cultivated seedbed. Mixes can also be over-sown into existing grassland if at least 50% of the sward is cleared to bare ground. Nitrogen fixation will be depressed if soil phosphate and pH are not at optimal levels.

Ongoing management

The key to delivering wildlife benefits from legume or herb-rich leys is to allow the clovers and other plants to fully flower before cutting, otherwise there will be no nectar or pollen available for bumblebees and other insects.

Efficient cutting and grazing can mean that there is little flowering to support wildlife, but a few minor changes can help to improve the flower resource of rotational legume- and herb-rich swards. In mown fields, consider delaying cutting until the majority of red clover has flowered, which will also help it persist in the sward. Consider also leaving strips or corners uncut and removing them at a later date.

In grazed fields, consider grazing at a taller sward height for a period of the summer to allow flowering or extending the rest period between grazing and minimising any topping throughout summer.

Some other key points to consider:

  • Some legumes require care when grazing to avoid bloat and high oestrogen levels affecting ovulation rates in breeding livestock.
  • Some legumes and herbs, such as red clover, are vulnerable to tight grazing, especially in winter. White clover will withstand a tighter grazing pressure.
  • Application of nitrogen fertiliser will reduce how much nitrogen is fixed from the atmosphere and the clover content of the herbage will drop.
  • If weeds become established, their management through chemicals is more challenging as many herbicides also affect legumes and herbs.
Close up of Bird's-foot trefoil, Ramsey Island RSPB reserve, Wales

In practice

Here are some useful case studies and articles about how farmers are putting Farm Wildlife into practice on their farms

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