Action: Add inorganic fertilizer (without planting)
- Three studies evaluated the effects of adding inorganic fertilizer (without planting) on peatland vegetation. Two studies were in bogs and one was in a fen meadow.
- Vegetation cover (1 study): One replicated, randomized, paired, controlled, before-and-after study in a bog in New Zealand reported that fertilizing typically increased total vegetation cover.
- Vegetation structure (1 study): One replicated, paired, controlled study in a fen meadow in the Netherlands found that fertilizing with phosphorous typically increased total above-ground vegetation biomass, but other chemicals typically had no effect.
- Overall plant richness/diversity (1 study): One replicated, randomized, paired, controlled, before-and-after study in a bog in New Zealand reported that fertilizing typically increased plant species richness.
- Growth (1 study): One replicated, controlled, before-and-after study in a bog in Germany found that fertilizing with phosphorous typically increased herb and shrub growth rate, but other chemicals had no effect.
- Other (3 studies): Three replicated, controlled studies in a fen meadow in Germany and bogs in Germany and New Zealand reported that effects of fertilizer on peatland were more common when phosphorous was added, than when nitrogen or potassium were added.
Inorganic fertilizers could be used to manage nutrients in peatlands and speed up revegetation. Plant growth might be limited by a lack of nutrients overall, or of a specific nutrient, after drainage, mining, vegetation harvest or pollution. Commonly added nutrients include nitrogen (N), phosphorous (P) and/or potassium (K).
Caution: Some peatlands are characterized by low nutrient availability (Rydin & Jeglum 2013). Adding fertilizer might be a short-term solution to encourage initial plant growth, but could lead to undesirable long-term increases in nutrient levels.
Key peatland types where this action may be appropriate: bogs, fens/fen meadows, tropical peat swamps.
Related action: add inorganic fertilizer to complement planting.
Rydin H. & Jeglum J.K. (2013) The Biology of Peatlands, Second Edition. Oxford University Press, Oxford.
Supporting evidence from individual studies
A replicated, paired, controlled study in 1994 in a degraded fen meadow in the Netherlands (van Duren et al. 1998) found that adding fertilizer increased plant biomass in 10 of 24 comparisons. The other comparisons were non-significant increases. After three months, above-ground vegetation biomass was greater in plots fertilized with phosphorous (80–370 g/m2) than in unfertilized plots (20–200 g/m2). The same was true for plots fertilized with phosphorous and nitrogen (220–460 g/m2) vs plots fertilized only with nitrogen (30–270 g/m2), and for plots fertilized with potassium, phosphorous and nitrogen (240–490 g/m2) vs plots fertilized with potassium and phosphorous or nitrogen (30–300 g/m2). In May 1994, 1 m2 plots (number not reported) were established in a rewetted fen meadow. Each plot received one fertilizer treatment: no fertilizer, N, P, K, N+P, N+K, P+K or N+P+K. Half of the plots were in an area stripped of topsoil. In August 1994, above-ground vegetation was harvested in a 60 x 60 cm quadrat in each plot, then dried and weighed.
A replicated, controlled, before-and-after study in 1995 in a historically mined raised bog in Germany (Sliva et al. 1999) found that fertilizer increased seedling growth in 15 of 48 comparisons, all involving phosphorous, but had no effect in the other 33 comparisons. After four months, seedlings in plots fertilized with phosphorous (either alone or in combination with nitrogen and potassium) were significantly taller than seedlings in unfertilized plots in 15 of 24 comparisons (for which fertilized: 2–18 cm; unfertilized: 1–4 cm). Seedlings in plots fertilized only with nitrogen or potassium were never significantly taller than unfertilized seedlings (0 of 24 comparisons; fertilized: 1–5 cm; unfertilized: 2–4 cm). In spring 1995, six 16 m2 plots of recently rewetted bare peat received each fertilizer treatment: N, P, K, or a mix of all three. Eight additional plots were not fertilized. After four months, all seedlings of six plant species (four herbs and two shrubs) were measured in every plot.
A replicated, randomized, paired, controlled, before-and-after study in 1998–2000 in a historically mined raised bog in New Zealand (Schipper et al. 2002) reported that fertilized plots typically contained more plant species and had greater vegetation cover than unfertilized plots. These results are not based on tests of statistical significance. After two years, fertilized plots contained more plant species than unfertilized plots in 11 of 12 comparisons (fertilized: 3–8 species; unfertilized: 2–6 species). Fertilized plots had greater cover of two peatland-characteristic plants: manuka Leptospermum scoparium in 6 of 9 comparisons (for which fertilized: 1–92%; unfertilized: 0–87%) and bamboo rush Sporadanthus ferrugineus in 5 of 9 comparisons (for which fertilized: 2–27%; unfertilized: 1–8%). Total vegetation cover was also higher in fertilized plots in 6 of 9 comparisons. In March 1998, twenty-four plots (each 25 m2) were established, in six blocks, on bare rewetted peat. Six plots (one random plot/block) received each fertilizer treatment: N, P, N+P, or none. None of these plots were sown. In June 2000, canopy cover was estimated for every plant species in each plot.
- van Duren I.C., Strykstra R.J., Grootjans A.P., ter Heerdt G.N.J. & Pegtel D.M. (1998) A multidisciplinary evaluation of restoration measures in a degraded Cirsio-Molinietum fen meadow. Applied Vegetation Science, 1, 115-130
- Sliva J. & Pfadenhauer J. (1999) Restoration of cut-over raised bogs in southern Germany – a comparison of methods. Applied Vegetation Science, 2, 137-148
- Schipper L.A., Clarkson B.R., Vojvodic-Cukovic M. & Webster R. (2002) Restoring cut-over restiad peat bogs: a factorial experiment of nutrients, seed and cultivation. Ecological Engineering, 19, 29-40