Action: Add lime to reduce acidity and/or increase fertility
Key messagesRead our guidance on Key messages before continuing
- One study examined the effect of liming (without planting) on peatland vegetation. The study was in a fen meadow. N.B. Liming is considered in different contexts here and here.
- Vegetation structure (1 study): One replicated, controlled study in a fen meadow in the Netherlands found that liming increased overall vegetation biomass (mostly grass).
Peatland plant survival and growth is partly determined by the acidity of a peatland, or pH (Rydin & Jeglum 2013). Fen plants grow in alkaline to weakly acidic peat (approximately pH 6–8, similar to saliva, tap water or sea water). Bog plants grow in more acidic peat (approximately pH 4–5, similar to tomato juice or coffee). Lime (calcium and/or magnesium-rich chemicals) can be added if the peat becomes too acidic for a desired plant community. Liming can reduce acidity. It can also affect nutrient availability: nutrients such as phosphorous become locked away in acidic soils (Weil & Brady 2016).
Caution: The benefits and harms of liming are very context specific. Because fen plants require the least acidic conditions, liming is mostly used to manage fens and fen meadows. Liming may be useful in some bogs that have become extremely acidic (e.g. as a result of exceptionally acidic rain). In most bogs, liming could cause damage by removing natural acidity.
Related interventions: rewetting, which may reverse drainage-related acidification of surface peat; restoring peatlands using multiple interventions, because lime is often used as part of a suite of interventions; add lime to complement planting.
Weil R.R. & Brady N.C. (2016) The Nature and Properties of Soils, Fifteenth Edition. Pearson, USA.
Rydin H. & Jeglum J.K. (2013) The Biology of Peatlands, Second Edition. Oxford University Press, Oxford.
Supporting evidence from individual studies
A replicated, controlled study in 1994 in a degraded fen meadow in the Netherlands (van Duren et al. 1998) found that limed plots contained more plant biomass after three months than unlimed plots. This was true in plots that had previously been stripped of topsoil (limed: 40; unlimed: 20 g/m2 biomass) and plots that had not been stripped (limed: 250; unlimed: 200 g/m2 biomass). The biomass was mostly established, dominant, velvety bentgrass Agrostis canina (precise contribution not reported). In May 1994, ten 1 m2 plots in a degraded, historically drained fen meadow were limed (approximately 500 g/m2). Ten additional plots were not limed. Five limed and five unlimed plots had been previously stripped of topsoil. In August 1994, above-ground vegetation was harvested in one 60 x 60 cm quadrat/plot, then dried and weighed.