Irrigate before or after seeding/planting
Overall effectiveness category Evidence not assessed
Number of studies: 2
Background information and definitions
In many arid areas low rainfall may limit the success of grassland restoration. Irrigating with water alongside seeding and planting may help to improve the probability of grassland plant establishment and colonization.
The studies detailed in this intervention are direct tests of the effectiveness of irrigating after seeding or planting (e.g. by comparison with an unirrigated 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 2006–2008 on five motorway verges in central Spain (Garcia-Palacios et al. 2010) found that irrigating after sowing non-native seeds increased plant cover but not plant diversity in most cases compared to sowing without irrigating. No statistical tests were carried out in this study. In six of 10 comparisons, overall plant cover was on average higher in plots that were irrigated and sown with seeds (54–89%) than in plots that were sown with seeds and not irrigated (49–71%), while in four comparisons plant cover was lower in irrigated plots (54–58% vs 55–65%). In four of 10 comparisons, plant diversity was higher in plots that were irrigated and sown with seeds than in sown plots that were not irrigated, while in six comparisons plant diversity was lower (data reported as Shannon diversity index). In December 2006, at each of five sites, two 1 × 1 m plots in each of six random blocks were sown with a commercial non-native seed mixture. One plot/block was irrigated in March–June 2007 and 2008 at a rate equivalent to 50% of the average monthly precipitation recorded in 1971–2000, while the other plot was not irrigated. In May 2007 and 2008, the cover of all plants was visually assessed in each plot.Study and other actions tested
A replicated, controlled study in 2008–2013 in a former arable field in Massachusetts, USA (Neill et al. 2015) found that adding water after sowing native grass and forb seeds did not alter the cover and species richness of native plant species or total plant species richness compared to sowing without adding water. In the first year after sowing, the average cover and richness of native plant species and total plant species richness did not differ significantly between plots with water added (native plants: 25–32% cover, 8–10 species/plot; total plants: 19–20 species/plot) and plots with no water added (native plants: 36% cover, 11 species/plot; total plants: 23 species/plot). The same was true five years after sowing (native plants: 51–58% vs 59% cover, 10 vs 10 species/plot; total plants: 18 vs 17 species/plot). In November 2008, fifteen 5 x 5 m plots were sown with locally collected native grass and forb seeds of 26 species. All plots were tilled before sowing to remove non-native vegetation. Water was added to 10 plots (190–380 l/plot) between June and August 2009, and five plots had no water added. Vegetation was surveyed in a 3 x 3 m quadrat placed in the centre of each plot in July or August 2009 and 2013.Study and other actions tested