Long-term effects of grass ley set-aside on erosion rates and soil organic matter on sandy soils in east Shropshire, UK

The contribution of ryegrass (Lolium perenne) ley set-aside to soil conservation and soil organic matter (SOM) content was investigated. Ten runoff plots (7–15°, 12–27% slope) at the Hilton Experimental Site, Shropshire, UK, were put to a grass ley in April 1991. Runoff and erosion rates during 9 years were low, despite the occurrence of potentially erosive rains. Mean runoff was 0.24 ± 0.20% (±S.D.) of precipitation (n = 89 plot-years), compared with a 15-year mean value of 0.13 ± 0.04% on permanent (control) grassland. Mean erosion rate was 0.21 ± 0.14 t ha−1 year−1 (n = 69 plot-years). Erosion rate and slope were poorly correlated, suggesting leys are highly effective for soil conservation. Mean SOM content increased consistently and significantly on the set-aside plots from 20.4 g kg−1 in 1991 to 31.1 g kg−1 in 2001. Contrary to the usually strong relationship between SOM and clay content, the percentage silt exhibited a stronger correlation with SOM than percentage clay content. Furthermore, there were equally strong correlations between SOM and cumulative particle size fractions of both clay and silt contents. In the absence of significant quantities of clay in these sandy soils, silts assist binding of SOM, which has significance for assessing soil carbon sequestration potential.