A traditional crop rotation is two or three years of cereals followed by an extended period of ley grass. Grass leys are usually mixtures of grasses and legumes, and are either cropped for hay or grazed by livestock.
The traditional way of establishing a ley is by undersowing. After a spring barley crop is conventionally drilled, grass and legume seed are spun and lightly harrowed in over the top. The barley is harvested normally and the grass and clover that has established beneath the crop is exposed.
Undersown leys are good for wildlife:
- They provide an uncultivated overwinter bridge which allows many insects to complete their life cycle in the soil. Sawflies pupate in the soil and emerge as adults from underown leys in spring. These adults lay eggs all through the neighbouring cereal crops and, by the time the game chicks hatch in mid-summer, there are lots of small sawfly caterpillers around for them to eat.
- Undersown barley, because it also contains clover and grass, supports a wider range of cereal insects than a conventional crop and is therefore better for game chick survival.
- They provide an instant fresh green sward in late summer when most of the rest of the landscape has turned a post-harvest brown.