The effects of nitrogen, potassium and phosphorus addition on the vegetation of a Somerset peat moor under cutting management

  • Published source details Kirkham F.W., Mountford J.O. & Wilkins R.J. (1996) The effects of nitrogen, potassium and phosphorus addition on the vegetation of a Somerset peat moor under cutting management. Journal of Applied Ecology, 33, 1013-1029.


In hay meadows in southwest England, fertilizer treatments have been shown to have significant effects on abundance of individual plant species and species diversity in the above-ground vegetation. This study investigated the effects of nitrogen, potassium and phosphorus addition on the vegetation of a peat moor under cutting management within the Somerset Moors and Levels Environmentally Sensitive Area (ESA).

b>Study area: The study was carried out in hay meadows on a peat moor in Tadham and Tealham Moors Site of Special Scientific Interest (SSSI) (51º 12'N, 2º49'W), Somerset, south-west of England. The plant communities corresponded to MG5 (crested dog's-tail Cynosurus cristatus-black knapweed Centaurea nigra meadow and pasture) and MG8 (Cynosurus cristatus-marsh marigold Caltha palustris flood pasture) of the UK National Vegetation Classification (Rodwell 1992).

Experimental design: In 1986, 57 plots (1.5 x 5 m) were laid out in a randomized block design, with three replicate blocks of 19 treatments within a fenced area to prevent livestock grazing. Granular fertilizer was applied by hand up to 4 times/year, from 1986 to 1989. A range of nitrogen (N), phosphorus (P) and potassium (K) fertilizer treatments were applied. No plot received more than 100 kg/ha of N on any one occasion.

Vegetation monitoring In May and October each year percentage composition of plant species was recoded in quadrats on plots cut for hay, followed by further cutting of aftermath growth. Samples were taken to calculate biomass production.

Vegetation analysis Effects of the fertilizer, cutting and grazing treatments on plant species richness, diversity and dominance was analysed. Ordination techniques were used to assess the affects of fertilizers on vegetation community composition.

Biomass production: P was more important than N in determining both biomass production and botanical change. In both cases, the effects were small when substantial amounts of N and K were applied without P, but when high rates of P were included biomass increased very significantly and species diversity was severely reduced, with Yorkshire fog Holcus lanatus, common sorrel Rumex acetosa and perennial ryegrass Lolium perenne dominating.

Main effects of fertilizer and grazing: L.perenne was not increased by N and modest rates of P in the absence of aftermath grazing, but dominated all plots with fertilizer applied when aftermath grazing was maintained. Velvet bent grass Agrostis canina eventually dominated plots receiving 200 kg/ha of N with modest rates of P and K in the absence of aftermath grazing, but was negatively associated with N where the aftermath was grazed.

Red clover Trifolium pratense became very abundant where P and K were applied with no or low levels (25 kg/ ha) of N each year, both with and without aftermath grazing, but all legumes were suppressed at high rates of N, particularly in conjunction with high P.

Substantial botanical change occurred on unfertilized plots as a result of the cessation of aftermath grazing. These plots became dominated by ribwort plantain Plantago lanceolata, with significant increases in rough hawkbit Leontodon hispidus and autumn hawkbit L.autumnalis.

Conclusions: The results of these experiments indicate that the prevention of fertilizer application and the maintenance of traditional aftermath grazing of vegetation regrowth after the hay cut, are necessary if the plant species diversity is to be sustained in Somerset hay meadows.


Rodwell J. (1992) British Plant Communities Vol.3. Grassland and Montane Communities. Cambridge University Press, Cambridge, UK.

Note: If using or referring to this published study, please read and quote the original paper.

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