Action: Create rotational grass or clover leys
- A controlled study in Finland found that creating clover leys resulted in higher spider abundance and fewer pest insects than a barley control plot. A study in the UK found that one-year ley plots had significantly lower earthworm species richness and abundance than three-and-a-half-year leys.
- A replicated study in the UK found that grass leys had fewer plant species than nine other conservation measures.
This intervention can be established on arable land by under-sowing spring cereal and leaving the under-sown sward to develop the following year. It can also be established through other means. The results of the intervention are monitored on the grass/clover ley.
See also ‘Undersow spring cereals, with clover for example’.
Supporting evidence from individual studies
A study of grass/clover ley fields on an arable site from 1950 to 1956 in the UK (Heath 1962) found that one-year ley plots had significantly lower earthworm species richness and abundance than three-and-a-half-year leys. One-year ley plots (within arable rotations) had lower numbers of species and overall abundance of earthworms (8-15/cubic foot) compared to three and a half-year ley plots (17-39/cubic foot). Overall earthworm weight showed the same trend (4 vs 8 g/cubic feet). One plot of each ley treatment was established in each of the six years. Leys were ploughed in the autumn and winter wheat sown. Plots were sampled for earthworms when they were ploughed out of leys (1953-1956). Four samples of two cubic feet of soil were sampled in each plot per year.
A replicated study in the summers of 1999-2000 on arable farms in the UK (Critchley et al. 2004) found that grass leys had fewer plant species than nine other conservation measures. Average numbers of plant species in the different conservation habitats were grass leys 3.1, wildlife seed mixtures 6.7, uncropped cultivated margins 6.3, undersown cereals 5.9, naturally regenerated grass margins 5.5, no-fertilizer conservation headlands 4.8, spring fallows 4.5, sown grass margins 4.4, overwinter stubbles 4.2, conservation headlands 3.5. Grass leys had the lowest number of plant species, lower than in undersown cereals, due to the later successional stage of the sown grass and clover Trifolium spp. species that dominated the leys. Plants were surveyed on a total of 294 conservation measure sites (each a single field, block of field or field margin strip), on 37 farms in East Anglia (dominated by arable farming) and 38 farms in the West Midlands (dominated by more mixed farming). The ten habitats were created according to agri-environment scheme guidelines. Vegetation was surveyed once in each site in June-August in 1999 or 2000 in thirty 0.25 m2 quadrats randomly placed in 50-100 m randomly located sampling zones in each habitat site. All vascular plant species rooted in each quadrat, bare ground or litter and plant cover were recorded.
A controlled trial from 2003 to 2004 in Jokioinen, southern Finland (Huusela-Veistola & Hyvanen 2006) found that fallow plots established by undersowing spring barley with grass or grass and red clover Trifolium pratense had more spiders (Araneae) and fewer pest insects than a control plot of spring barley, but similar numbers of ground beetles (Carabidae). For example, there were 28-35 spiders/ trap, compared to around 5 spiders/trap in the control plot. The only difference between seed mixtures used was that the plot sown with red clover in the mix had fewer unsown plant species (around 2 species/m2), but higher plant biomass, than control cereal fields, which had around 16 plant species/m2. The plot undersown with just grasses had around 6 plant species/m2. There was no difference in the numbers of spiders, beetles, flying insects or unsown plant species, between two year grass or grass-clover fallow plots established by undersowing spring barley, and similar plots sown without accompanying cereals. The fallow treatments were established in 2003, each on a 44 x 66 m plot. A control plot was sown with spring barley in 2004. Insects were sampled using a yellow sticky trap and three pitfall traps in the centre of each plot for a week in June, July and August 2004. Unsown plant species were counted in four 50 x 50 cm quadrats in each plot in late August 2004.
- Heath G.W. (1962) The influence of ley management on earthworm populations. Grass and Forage Science, 17, 237-244
- Critchley C., Allen D., Fowbert J., Mole A. & Gundrey A. (2004) Habitat establishment on arable land: assessment of an agri-environment scheme in England, UK. Biological Conservation, 119, 429-442
- Huusela-Veistola E. & Hyvanen T. (2006) Rotational fallows in support of functional biodiversity. IOBC/wprs Bulletin, 29, 61-64