Herbal leys (or diverse swards) are sown pastures made up of a mix of grasses, herbs and legumes. Together they deliver soil fertility, biology and structure, boost livestock health, encourage biodiversity and are productive with low rainfall.
Sheep on herbal leys, Oak Farm, Devon (Bex Tyers)
Sainfoin
Diversity is key
Each species has different functions, which makes the mixture work better overall. They improve the soil in different ways, producing greater yields, and also have different nutritional functions.
Choosing the right mix of seeds is key, and depends on your soil type, geography and desired outcomes. A mixture can include anything from 3 to 30 species, though a minimum of 6 is usually about right to get a good range of functions.
Cows in diverse sward (Rob Thornhill)
Yarrow
Planning is crucial, so think about:
How establishing the ley fits within your arable rotation or other temporary grass reseeds.
Achieving the best seed bed preparation possible (cultivate/harrow to fine tilth, roll, ideally
broadcast sow, then roll and roll again! If drilling, ensure max 1cm depth. Over-sowing
can be successful but destroy as much competition as possible).
Timing of sowing – see 'Likely timescales', below.
When to start grazing (i.e. if autumn sowing, light graze before winter).
When to rest leys. You need to account for fencing, water provision and shelter.
Sowing a diversity of plants with differing growth rates (which leads to a longer
growing season overall).
Allowing areas of the sward to flower and set seed to replenish the seedbank
and provide food for wildlife.
Likely timescales
Four years is considered an optimal length for herbal leys in the rotation, to allow for root growth, soil fertility building and high species diversity. Longer periods will be even better for the soil, but you are likely to see a decline in species diversity unless it is very carefully managed.
Timing of sowing
Warm soil is needed for germination (8-10°c), along with good levels of soil moisture – so sow in August/early Sept or later in April/May once soil has warmed. Be careful not to over graze too early (6-8 weeks post establishment).
Function: Access moisture from deep down while sinking carbon into soil; Tap roots break up compaction and rooting mat provide a ‘sponge’ in wet soils. Benefit: Carbon is less likely to be released; improves infiltration and drainage; increased resilience to low rainfall.
Chicory
Anthelmintics
Chicory, Sainfoin, Birdsfoot trefoil
Function: Contain high levels of condensed tannins. Benefit: Reduces worm burden.
Function: Mine minerals from the soil making them available to livestock. Benefit: Provides naturally rich source of minerals, reducing need to buy them in.
Plantain
Flowering plants
Burnet, Chicory, Birdsfoot trefoil, Lucerne
Function: Food for pollinators. Benefit: Attract beneficial predators and increase biodiversity.
Lucerne
The financials
Pros
Saving on fertiliser (nitrogen fixing plants can fix up to 250 kg N/ha).
Saving costs of mineral feed plus supplementary feeding in drought.
Increased yields – different plants, when grown together, can yield 50% more than an average rye grass sward.
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