Disturb soil before seeding/planting
Overall effectiveness category Evidence not assessed
Number of studies: 7
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Background information and definitions
Before sowing seeds of grassland plants, soil is regularly disturbed by ploughing or tilling. This disturbance may help plants to become established by reducing competition with other plants, such as grasses. The studies detailed in this intervention are direct tests of the effectiveness of disturbing soil before seeding or planting (e.g. by comparison with an undisturbed but seeded or planted plot). 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 disturbing soil by rotovating before sowing seeds increased grass and forb species richness in most cases compared to harrowing before sowing. No statistical analyses were carried out in this study. In seven of 12 comparisons, there were more grass species in plots where soil was rotovated and seeds sown (5–12 species/plot) than in plots where soil was harrowed and seeds sown (4–9 species/plot). In the five other comparisons, the number of grass species did not differ between plots that were rotovated or harrowed before sowing (both 8–13 species/plot). In all of 12 comparisons, there were more forb species in plots where soil was rotovated and seeds sown (7–25 species/plot) than in plots where soil was harrowed and seeds sown (3–21 species/plot). In 1994, at each site, eight 6 x 4 m plots were mown. In four plots/site, the soil was disturbed by rotovating (to give 50% bare ground), while the other four plots were harrowed. 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, paired, controlled study in 1993 on road verges in California, USA (Brown & Bugg 2001) found that disturbing soil before sowing forb seeds increased the emergence and cover of sown forbs compared to sowing seeds alone, but disturbing the soil before planting forb seedlings had no effect on seedling growth. Plots where soil was disturbed before sowing had greater emergence (11%) and cover (97%) of sown forbs than plots where soil was not disturbed before sowing (7% and 14% respectively). However, the proportion of planted forb seedlings showing aboveground growth did not differ significantly between disturbed and undisturbed plots (data not reported). In January 1993, five blocks, each with three 7.62 x 7.62 m plots, were established on grass verges. In each block, one plot was tilled to a depth of 10–15 cm and sown with seeds of seven native forb species, while one plot was not tilled but was sown with seeds. In January–April 2003, thirty seedlings of each of two forb species, narrow-leaf milkweed Asclepias fascicularis and blue-eyed-grass Sisyrinchium bellum, were planted 30 cm apart in each plot. In April 1993, cover and emergence of forbs was estimated in two 0.5 x 0.25 m quadrats/plot. Aboveground growth of seedlings was assessed in each plot in March–May 1993.Study and other actions tested
A replicated, randomized, paired controlled study in 1998–1999 in a species-poor grassland near Göttingen, Germany (Hofmann & Isselstein 2004) found that disturbing soil before sowing seeds increased the emergence of seedlings for seven of eight wildflower species compared to sowing alone. After one year, the average percentage of seedlings that emerged for seven of eight wildflower species was higher in plots where soil was disturbed before sowing (19–32%) than in plots where soil was not disturbed before sowing (11–22%). For one wildflower species, seedling emergence did not differ significantly between plots where soil was disturbed (14%) or not disturbed (13%) before sowing. In 1998, blocks were established at the site (replication unclear from study). A rake was used to disturb the soil and vegetation in 0.5 × 0.5 m plots and wildflower seeds were sown, while in other plots seeds were sown but soil and vegetation were not disturbed (number for each not reported). Emergence of seedlings was recorded in each plot in July 1999.Study and other actions tested
A replicated, controlled study in 1998–2000 at a grassland site in West Yorkshire, UK (Westbury et al. 2006) found that disturbing soil before sowing seeds did not alter plant species richness, diversity, or total biomass compared to sowing alone. After 1–2 years, plots that were disturbed before sowing had on average a similar number of total plant species (12.7–14.4), sown species (2.6–6.2), unsown species (8.2–10.1), plant diversity (data reported as Shannon diversity index) and above-ground biomass (140–450 g/m2) to plots that were not disturbed before sowing (total plant species: 12.3–12.4; sown species: 2.7–5.4; unsown species: 7–9.7; biomass: 210–490 g/m2). In autumn 1998, six plots (each 4 x 4 m) were created on a newly established meadow. Three plots were disturbed using a lawn scarifier to a depth of 2 cm, while three plots were left undisturbed. In April 1999, all six plots were sown with a commercial seed mix of six grass and six forb species at a rate of 30 kg/ha. All plots were cut annually in July. In May 1999 and 2000, vegetation was assessed within three randomly placed 50 x 50 cm quadrats/plot.Study and other actions tested
A replicated, randomized, paired, controlled study in 2005–2006 in a degraded steppe grassland in Hebei province, northern China (Liu et al. 2008) found that disturbing soil before sowing seeds increased plant emergence, survival, and seedling density compared to sowing alone. The percentage of seeds from which plants emerged was higher where soil had been disturbed prior to seeding (57%) than in areas where soil had not been disturbed before seeding (40%). After one year, a similar pattern was also seen for seedling survival (disturbed: 5.4%; undisturbed: 0.4%) and seedling density (disturbed: 14 seedlings/m2; undisturbed: 3 seedlings/m2). Before seeding, soil was disturbed in half of all 2 × 2 m plots using a rake and half of the plots remained undisturbed (replication of experiment unclear). Seeds were collected in Saibei administrative region in autumn 2004. In June 2005, seeds were sown in all plots at a density of 400–1,200 seeds/m2 and soil compressed using a roller. Plots were fenced to prevent damage from livestock and sprayed with pesticides. Seedling density and survival was monitored between June 2005 and August 2006.Study and other actions tested
A replicated, controlled study in 2006–2007 in arid steppe grassland in northeastern Spain (Pueyo et al. 2009) found that disturbing soil by ploughing and sowing seeds or planting did not alter survival of planted plants or seed germination compared to sowing alone. Survival of Mediterranean saltwort Salsola vermiculata and esparto grass Lygeum spartum plants did not differ significantly between areas that were ploughed (22–70%) and areas that were not ploughed (0–73%). Seed germination of the two species also did not differ significantly (ploughed and seeded: 0%; seeded, not ploughed: 0–2%). In the planting experiment, in October 2006, the soil was ploughed to a depth of 30–40 cm and twenty-five Mediterranean saltwort and esparto grass seedlings were planted four metres apart, while another twenty-five plants were planted in an area that was not ploughed. Seeding was carried out nearby to the planting experiment. Survival of planted seedlings was recorded in February and September 2007. Seed germination was recorded in March, June and September 2007.Study and other actions tested
A replicated, controlled study in 2014–2015 in 73 agricultural grasslands in Brandenburg, Thuringia and Baden-Württemberg, Germany (Klaus et al. 2016) found that disturbing soil before sowing seeds led to an increase in plant and seedling species richness and number of seedlings compared to sowing alone. After 7–19 months, plots that were disturbed before seeds were sown had on average a greater species richness of plants (36 species/quadrat) and seedlings (14 species/quadrat) than plots that were not disturbed before seeds were sown (27 plant species/quadrat; 5 seedling species/quadrat). Disturbed and sown plots also had more seedlings/quadrat (average 251 seedlings) than undisturbed and sown plots (average 94 seedlings). Two 7 x 7 m plots were established in each of 73 grasslands. The soil was disturbed in one plot (using rotovation tilling or a rotary harrow in October 2014) before seeds were sown, the other was left undisturbed. A mix of native grass, legume and herb seeds (47–66 region-specific species) combined with sand and crushed soybean was sown in each plot in November 2014 and March 2015. Vegetation was monitored within a 2 x 2 m quadrat in each of the 146 plots on three occasions in May–June 2015.Study and other actions tested
Where has this evidence come from?
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This Action forms part of the Action Synopsis:Grassland Conservation
Grassland Conservation - Published 2021