Herbal Leys Have No Effect on Soil Porosity, Earthworm Abundance, and Microbial Community Composition Compared to a Grass-Clover Ley in a Sheep Grazed Grassland after 2-Years

Herbal leys (multispecies swards) can potentially deliver greater agronomic and environmental benefits than conventional grass-clover swards in grazed agroecosystems. However, despite their popularity in agri-environment schemes, little is known about the effect of herbal leys on soil physical (e.g., porosity), chemical (e.g., carbon), and biological (e.g., soil fauna) characteristics. In the UK, a 2-ha replicated-field experiment utilising a herbal or grass-clover ley (n = 3 per sward) aimed to investigate the effect of sward type on soil quality. Each sward was rotationally grazed by weaned lambs (3.2 LU ha(-1)) over two grazing seasons, with soil physiochemical and biological characteristics assessed after 2-years using techniques such as X-ray micro-Computed Tomography (mu CT) and microbial shallow shotgun sequencing. Soil chemical characteristics (e.g., pH) were unaffected by sward type. Similarly, topsoil (0-10 cm) organic carbon stocks measured after 2-years did not differ between the herbal (26.1 +/- 1.1 t C ha(-1)) and grass-clover ley (25.7 +/- 1.1 t C ha(-1)). X-ray mu CT analysis revealed greater pore connectivity (Euler number) in grass-clover ley intact soil cores (0-10 cm depth, 7.5 cm width) than herbal ley cores dominated by Plantago lanceolata (p = 0.008). However, there was no sward-type difference in aggregate stability or general pore characteristics, determined using X-ray mu CT, in air-dried 4 mm aggregates obtained from 0-5 or 5-10 cm depth, nor did sward type affect earthworm abundance, microbial community composition or the functional gene profile. This study is the first to explore the effects of a commercial herbal ley on physical, chemical, and biological soil quality indicators in a rotationally grazed sheep pasture. While no improvements in soil quality indicators were observed after 2-years, these findings have significant implications for agri-environment schemes promoting herbal leys to achieve soil quality and sustainability, with further research needed to optimise the seed mixture and management regime to deliver greater long-term below-ground ecosystem service benefits.