Remove topsoil or turf before seeding/planting
Overall effectiveness category Evidence not assessed
Number of studies: 6
Background information and definitions
Conversion of grasslands to arable agriculture or pasture often leads to soils with high nutrient content. These high nutrient content soils promote the growth of grass species which can outcompete forb species. In addition, these soils may contain seeds of undesirable plants (e.g. crop seeds). Removing topsoil may help to reduce soil nutrient content as well as eliminating the seeds of undesirable species. Sowing seeds after the removal of topsoil may aid colonisation by grassland plants.
The studies detailed in this intervention are direct tests of the effectiveness of removing topsoil/turf before seeding or planting (e.g. by comparison with a seeded or planted plot with topsoil/turf left in place). Studies that represent comparisons of seeding to unseeded plots can be found in the actions ‘Sow grass seeds’, ‘Sow grassland forb species’ or ‘Sow native grass and forbs’.
Supporting evidence from individual studies
A replicated, randomized, paired, controlled study in 1994–1996 in six improved grassland sites in England and Wales, UK (Hopkins et al. 1999) found that removing turf before sowing seeds increased grass and forb species richness in most cases compared to disturbing soil before sowing. No statistical analyses were carried out in this study. In eight of 12 comparisons, there were more grass species in plots where turf was removed and seeds sown (10–15 species/plot) than in plots where soil was disturbed and seeds sown (4–13 species/plot). In the four other comparisons, the number of grass species was similar in plots that had turf removed or soil disturbed before sowing (both 7–12 species/plot). In 10 of 12 comparisons, there were more forb species in plots where turf had been removed and seeds sown (11–28 species/plot) than in plots where soil was disturbed and seeds sown (3–25 species/plot). In the two other comparisons, the number of forb species was similar in plots that had turf removed (10–12 species/plot) or soil disturbed (8–13 species/plot) before sowing. In 1994, at each site, twelve 6 x 4 m plots were mown. In four plots/site, turf was removed to a depth of 3 cm. In eight plots/site, soil was disturbed by harrowing (four plots) or rotovating (four plots). Seed mixes (five grass species and 18 forb species) were sown at a rate of 12–14 kg/ha in all plots in early August 1994. In May/June of 1995 and 1996, three 40 x 40 cm quadrats were placed in each plot and the frequency of each grass and forb species recorded.Study and other actions tested
A replicated, randomized, controlled study in 1994–1999 in a species-poor wet pasture in the UK (Tallowin & Smith 2001) found that removing topsoil before planting seedlings led to higher cover of planted species and lower cover of common knapweed Centaurea nigra compared to planting without topsoil removal. No statistical analyses were carried out in this study. Cover of planted Cirsio-Molinietum species was higher in plots where topsoil was removed before planting (41–68%) than in plots where topsoil was not removed before planting (29–40%). Cover of common knapweed was lower in plots where topsoil was removed before planting (5–12%) than in plots where topsoil was not removed (50–68%). In May 1994, ten 2 x 2 m plots were rotovated. Topsoil was removed to a depth of 15–20 cm in five plots, while topsoil was not removed in the five other plots. In May 1995, all plots were sprayed with glyphosate herbicide and seedlings of 14 species planted. Cover of all species was assessed in each plot every year between 1997 and 1999.Study and other actions tested
A replicated, randomized, controlled study in 2002–2004 in two coastal prairies in California, USA (Buisson et al. 2006) found that removing topsoil before planting California oatgrass Danthonia californica plants increased their survival compared to planting without topsoil removal. After 18 months, survival of California oatgrass plants was higher in areas where topsoil was removed and plants planted (39%) than in areas where topsoil was not removed and plants were planted (12%). In each site, in August 2002 topsoil was removed from twenty-four 1.5 × 1.5 m plots to a depth of 10 cm by tilling, while topsoil was not removed from 24 plots. In January 2003, four California oatgrass plants were planted in each plot. Survival of plants in each plot was recorded in March, June and December 2003 and June 2004.Study and other actions tested
A replicated, paired, controlled study in 2002–2004 in a coastal grassland in California, USA (Buisson et al. 2008) found that removing topsoil before sowing and planting purple needlegrass Nassella pulchra increased seedling and transplant survival. After 17 weeks, more purple needlegrass seedlings had emerged and survived in plots where topsoil was removed before sowing (41–53%) than in plots where topsoil was left intact before sowing (13–27%). After 1.5 years, the survival of purple needlegrass transplants was higher in plots where topsoil was removed before planting (20–28%) than in plots where topsoil was left intact (5–15%). In August 2002, twenty-four 0.75 x 1.5 m plots were established in exotic grass and forb patches. Topsoil was removed to a depth of 10 cm from 12 of the plots by tilling and scraping, while in 12 plots topsoil was left intact. Half of each plot was sown with 25 locally-collected purple needlegrass seeds in October 2002, and half was planted with four purple needlegrass transplants in January 2003. Seedling number and survival were recorded in each plot until March 2003. Transplant survival was recorded until June 2004.Study and other actions tested
A replicated, controlled study in 2001–2007 in a former landfill site in Somerset, UK (Carrington & Diaz 2011) found that removing topsoil before sowing with a commercial seed mix increased the number of seeded species compared to seeding alone. The number of seeded plant species was higher in areas where topsoil was removed and seeds sown (6.4–10.2 species/plot) than in areas where topsoil was not removed but seeds were sown (1.7–5.2 species/plot). In 1998, the landfill site was decommissioned and covered with clay to a depth of 1 m to which topsoil and compost were added to a depth of 15–20 cm. In June 2001, topsoil was removed from six 10 × 10 m plots to a depth of 15 cm, while soil was not removed from six other plots. In June 2001, a commercial seed mix of 22 species was sown at a rate of 1.8 g/m2 in all plots. The presence of all plant species was recorded annually in June 2003–2007 using two randomly located 1-m2 quadrats in each plot.Study and other actions tested
A replicated, randomized, controlled study in 2009–2012 in a former orchard in the south of France (Jaunatre et al. 2014) found that removing topsoil before sowing seeds increased plant species richness and the similarity of the plant community to that of intact steppe, but did not alter vegetation cover. After three years, average plant species richness was higher in plots where topsoil was removed before seeds were sown (23 species/quadrat) than in plots where topsoil was not removed before seeds were sown (10 species/quadrat). Plant community similarity to an intact steppe site was also higher in plots where topsoil was removed before sowing than in plots where topsoil was not removed (data reported as Bray-Curtis similarity). Vegetation cover did not differ significantly between plots where topsoil was removed (55%) or not removed (67%) before sowing. In 2009, all trees were removed from the site and soils were levelled. Topsoil was removed (to a depth of 20 cm) and seeds of three nurse plants were sown in three randomly selected 10 x 10 m plots. No topsoil was removed and seeds were sown in two 30-ha plots. Sheep grazing was reintroduced in 2010. In May 2012, vegetation was recorded in nine 2 x 2 m quadrats in plots where topsoil was removed and seeds sown, and in eighteen 2 x 2 m quadrats in plots where no topsoil was removed and seeds sown and in an adjacent intact steppe site.Study and other actions tested