Add inorganic fertilizer (before/after planting)
Overall effectiveness category Trade-off between benefit and harms
Number of studies: 9
Background information and definitions
Inorganic fertilizer can provide nutrients that are in short supply, thereby increasing the initial survival and/or growth rate of introduced plants. Commonly added nutrients include nitrogen (N), phosphorous (P) and/or potassium (K). These are major nutrients that are most commonly limiting for plant growth in peatlands (Rydin & Jeglum 2013). Fertilizer is usually added immediately before or immediately after planting. Note that we do not include studies that only report responses of nurse plants (e.g. Caporn et al. 2007).
Caution: 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. Some studies involve planting trees, but trees are not natural features of many peatlands.
Key peatland types where this action may be appropriate: bogs, fens/fen meadows, tropical peat swamps.
Caporn S., Sen R., Field C., Jones E., Carroll J. & Dise N. (2007) Consequences of lime and fertilizer application for moorland restoration and carbon balance. Moors for the Future Research Report.
Rydin H. & Jeglum J.K. (2013) The Biology of Peatlands, Second Edition. Oxford University Press, Oxford.
Supporting evidence from individual studies
A controlled, before-and-after study in 1991 in a historically mined raised bog in England, UK (Money 1995) found that fertilization increased growth of planted Sphagnum mosses in three of four cases. In pools with no other intervention, both Sphagnum species grew faster when fertilized than when not fertilized (feathery bog moss Sphagnum cuspidatum 30% faster and recurved bog moss Sphagnum recurvum 85% faster). Amongst limed pools, only feathery bog moss grew faster (35%) when fertilized. In limed pools, fertilizer had no effect on recurved bog moss growth. In 1991, individual Sphagnum plants (cut to 5 cm length) were submerged (30 cm deep) in 4 m3 pools dug in the bog (number of plants and pools not reported). After 10 days, four treatments were applied: fertilization and liming, fertilization only, liming only, or none. Fertilized pools received 30 g sodium phosphate. Limed pools received 80g calcium carbonate. The length of all plants was measured after 20 weeks.Study and other actions tested
A replicated, controlled, before-and-after study in 1991–1995 in a historically mined raised bog in Germany (Sliva & Pfadenhauer 1999) found that fertilization increased growth of two of three planted herb species. One year after fertilization, there were more shoots on fertilized than unfertilized sedge Carex rostrata (142 vs 45 shoots/plant) and common cottongrass Eriophorum angustifolium (6 vs 2 shoots/plant). However, sheathed cottongrass Eriophorum vaginatum tussocks had similar diameters whether fertilized (69 cm) or not (70 cm). In 1991, twelve 3 x 35 m plots of bare rewetted peat were planted with the shoots and tussocks (one plant/3 m2). At this point, plants destined to be fertilized and unfertilized did not differ in shoot number or tussock diameter. In 1994, six of the plots were fertilized (mixture of N, P and K compounds; 100 g/m2). In 1995, shoot number and tussock diameter were re-measured on each plant.Study and other actions tested
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 fertilization had mixed effects on cover of two sown plant species after 810 days. These results are not based on tests of statistical significance. Fertilizer that included phosphorous increased cover of manuka Leptospermum scoparium (or did not reduce it from 100%) in all six cases, but fertilizing only with nitrogen reduced cover in all three cases. Fertilization increased cover of bamboo rush Sporadanthus ferrugineus in five of six cases on tilled plots (fertilized: 3–11%; unfertilized 1–2%), but reduced rush cover in all three cases on raised plots (fertilized: 0–6%; unfertilized: 32%). In March 1998, forty-eight 25 m2 plots were established, in six blocks, on bare rewetted peat (some tilled and some raised). All plots were sown with manuka or bamboo rush seeds. For each plant species, six plots (one random plot/block) received each of four fertilizer treatments: N (100 kg/ha), P (50 kg/ha), N+P, or none. In June 2000, canopy cover of every plant species was estimated. This study also reported the effect of fertilization in unsown plots (see intervention Add inorganic fertilizer without planting).Study and other actions tested
A replicated, randomized, paired, controlled study in 1990–2002 in a historically mined bog in Quebec, Canada (Bussières et al. 2008) found that fertilization reduced survival of one planted tree species (no effect on three others) but increased growth of one species (no effect on one other). After three growing seasons, fertilized black spruce Picea mariana saplings had lower survival rates (24–65%) than unfertilized saplings (75%). Fertilization did not significantly affect survival of tamarack Larix laricina, red maple Acer rubrum or poplar Populus spp. (fertilized: 1–76%; unfertilized: 16–85%). In the third growing season, tamarack grew more with a low fertilizer dose (shoot length 59–65 cm) than a high dose (46 cm) or no fertilizer (39 cm). Fertilizer did not affect growth of black spruce. In early summer 2000, seedlings of each tree species were planted into bare, slightly drained peat. There were 2–7 single-species blocks/species. Within each block there were three fertilized plots (mixture of N, P and K compounds; 122.5 g/plant, 245 g/plant or 490 g/plant) and one unfertilized plot. In August 2002, seedling survival was assessed. Terminal shoot length was measured for nine trees (across three evenly spaced quadrats) in each plot.Study and other actions tested
A replicated, randomized, paired, controlled study in 2004–2005 in a historically mined bog in Quebec, Canada (Caisse et al. 2008) reported that fertilization increased survival and growth rate of two planted tree species. These results were not tested for statistical significance. After two growing seasons, survival of fertilized tamarack Larix laricina was 92–98% (unfertilized: 81%) and of fertilized black spruce Picea mariana 58–87% (unfertilized: 55%). As a measure of growth rate, shoot length of fertilized tamarack was 9–33 cm (unfertilized: 1 cm) and of fertilized spruce 4–6 cm (unfertilized: 3 cm). In early June 2004, seedlings of the two tree species were planted into drained bare peat. There were three blocks/species. Within each block, six plots of 150 trees immediately received a random fertilization treatment (commercial or custom-made; see original paper). Three additional plots of 50 trees were not fertilized. In October 2005, seedling survival was assessed. Terminal shoot length was measured for 15 trees (across five randomly placed quadrats) in each plot.Study and other actions tested
A replicated, randomized, controlled study in 2005–2006 in two historically mined bogs in New Brunswick, Canada (Caisse et al. 2008) reported that fertilization increased growth of planted trees in 8 of 14 combinations: only when the fertilizer included phosphorous. These results are not based on tests of statistical significance. After two growing seasons, trees fertilized with phosphorous had longer shoots (black spruce Picea mariana: 13–23 cm; tamarack Larix laricina: 46–65 cm) than unfertilized trees (spruce: 7 cm; tamarack: 2 cm). Trees fertilized only with nitrogen or potassium had similar-length shoots to unfertilized trees (spruce: 4–6 cm; tamarack: 2–3 cm). Saplings were originally planted into bare peat in spring 2001. In spring 2005, four plots of each tree species (one random plot in each of four blocks) received each fertilization treatment: no fertilizer, N (40 g/plant), P (9 g/plant), K (15 g/plant), N+P, N+K, P+K or N+P+K. In October 2006, terminal shoot length of eight trees was measured in each plot.Study and other actions tested
A replicated, randomized, paired, controlled, before-and-after study in 2004–2006 in a historically mined bog in Quebec, Canada (Graf & Rochefort 2008) found that fertilizing plots sown with vegetation fragments increased cover of sedges Carex spp., but had no effect on cover of other vegetation or plant species richness. Before sowing, all plots were bare peat. After two years, sedge Carex spp. cover was higher in fertilized plots (8%) than unfertilized plots (2%). However, there was no significant difference between fertilized and unfertilized plots for vegetation cover (fertilized: 53%; unfertilized: 47%), Sphagnum moss cover (fertilized: 21%; unfertilized: 29%), total herb cover (data not reported) or plant species richness (data not reported). In May–August 2004, vegetation fragments from Sphagnum-dominated fens were spread onto five pairs of cleared and levelled 5 x 6 m plots. Note that the aim of this study was to create a fen, as the post-mining peat chemistry was more like a fen than a bog. Five plots (one random plot/pair) were fertilized with rock phosphate (15 g/m2). The other plots were not fertilized. All plots were mulched with straw. In September 2006, cover of every plant species was estimated in 10–20 quadrats/plot.Study and other actions tested
A replicated, randomized, controlled, before-and-after study in 2011 in a nursery in Indonesia (Yuwati et al. 2014) found that fertilization typically had no effect on growth of planted tree seedlings. Seedlings of 22 peat swamp tree species were studied. For 14–22 species (depending on the chemicals in the fertilizer), fertilized and unfertilized seedlings showed similar height growth. Similarly, fertilization had no significant effect on stem diameter of 16–18 species and dry mass of 19–20 species. The remaining species showed mixed responses: fertilization increased growth of some but reduced growth of others. In June 2011, 10 random seedlings of each species received each fertilizer treatment (36.8 mg of each nutrient twice/week): N, N+P, N+P+K or none. Seedlings were grown in pots of soil and rice husk, from seed or transplanted from the wild. The duration of the experiment was not reported.Study and other actions tested
Referenced paperYuwati T.W., Rachmanadi D., Santosa P.B., Rusmana . & Graham L.L.B. (2014) Response of peat swamp forest species to macronutrients. Pages 46-63 in: F.R.U. Banjarbu, . FORDA & L.L.B. Graham (eds.) Tropical Peat Swamp Forest Silviculture in Central Kalimantan. Kalimantan Forests and Climate Partnership, Indonesia.
A replicated, randomized, paired, controlled study in 2011–2013 in a historically mined bog in Quebec, Canada (Rochefort et al. 2016) found that fertilizing plots sown with vegetation fragments increased total vegetation cover, vascular plant cover and bryophyte cover. After two years, fertilized plots had significantly greater cover than unfertilized plots of total vegetation (fertilized: 44%; unfertilized: 21%), vascular plants (fertilized: 35%; unfertilized: 18%) and bryophytes (fertilized: 9%; unfertilized: 3%). Nine pairs of 20 m2 plots were established on a historically mined bog. The plots had been sown with mixed vegetation fragments from a donor fen in winter 2009/2010. Note that the aim of this study was to create a fen, as the post-mining peat chemistry was more like a fen than a bog. In July 2012, nine plots (one plot/pair) were fertilized with rock phosphate (25 g/m2). The other plots were not fertilized. In July 2014, vegetation cover was estimated in six quadrats/plot: vascular plants in three 1 x 1 m quadrats and bryophytes in three 50 x 50 cm quadrats.Study and other actions tested