Add inorganic fertilizer: freshwater marshes
Overall effectiveness category Unknown effectiveness (limited evidence)
Number of studies: 1
Background information and definitions
Fertilizers can be used to manage nutrient availability and may 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. When one or two nutrients are overabundant, invasive plant species may benefit more than native species. Adding the less abundant nutrients may shift the competitive balance back towards native species (Tilman et al. 1999; Perry et al. 2004). Commonly added nutrients include nitrogen (N), phosphorous (P) and/or potassium (K). It may be sensible to add fertilizer when the focal site is not flooded, to reduce the risk of it dissolving or being washed away.
The effects of this action will be heavily dependent on the study context, especially initial site nutrient levels and the amount of fertilizer added. Adding fertilizer when nutrients are already abundant could cause more harm than good, encouraging the growth of undesirable plants or algae and even inhibiting plant growth (Weinbaum et al. 1992). Accordingly, studies testing the effects of nutrient enrichment as a threat (i.e. enrichment above normal or desirable levels) are not summarized as evidence.
Perry L.G., Galatowitsch S.M. & Rosen C.J. (2004) Competitive control of invasive vegetation: a native wetland sedge suppresses Phalaris arundinacea in carbon-enriched soil. Journal of Applied Ecology, 41, 151–162.
Tilman E.A., Tilman D., Crawley M.J. & Johnston A.E. (1999) Biological weed control via nutrient competition: potassium limitation of dandelions. Ecological Applications, 9, 103–111.
Weinbaum S.A., Johnson R.S. & DeJong T.M. (1992) Causes and consequences of overfertilization in orchards. HortTechnology, 2, 112–121.
Supporting evidence from individual studies
A replicated, paired, controlled, before-and-after study in 1987–2007 in two wet grasslands in northwest Germany (Poptcheva et al. 2009) reported that fertilized plots contained more plant biomass than unfertilized plots after 4–18 years, but that fertilizer had no consistent effect on vegetation cover, height or species richness. In the first year of the study, above-ground vegetation biomass was statistically similar in fertilized plots (540–590 g/m2) and unfertilized plots (480–510 g/m2). However, after 4–18 years of intervention, above-ground vegetation biomass was significantly greater in fertilized plots (520–820 g/m2) than unfertilized plots (240–390 g/m2). Over 20 years, other vegetation metrics did not respond clearly or consistently to fertilization across the two wet grasslands (data reported as graphical analyses; statistical significance of differences not assessed). These metrics included cover of plant groups (e.g. sedges, rushes, forbs), vegetation height, species richness and community moisture preference. Methods: In 1987, two plots (each 200–250 m2) were established in each of two wet grassland sites (with non-peaty soils, and maintained as fertilized pasture prior to the study). From 1987, all four plots were mown twice each year (June/July and September). From 1989, one plot in each meadow was also fertilized each year in early spring (60 kg/ha P2O5 and 120 kg/ha K2O). Vegetation was surveyed in mid-June. Cover/abundance of all plant species was recorded in four 4-m2 quadrats/plot, every one or two years between 1987 and 2007. Vegetation was cut from eight 0.25-m2 quadrats/plot in 1989, 1993, 1998 and 2007, then dried and weighed.Study and other actions tested