Experimental assessment of the effects of nitrogen addition under hay-cutting and aftermath grazing on the vegetation of meadows on a Somerset peat moor.
Abstract
Tadham Moor, a species-rich lowland moor, was given 0, 25, 50, 100 or 200 kg N/ha annually. Treatments with applied N were given replacement levels of P and K after cutting. The area was cut for hay in early July, and the aftermath was grazed by cattle. Fertilizer application encouraged grasses (notably Lolium perenne and Holcus lanatus) which came to dominate the sward at the expense of most other species. All measures of species diversity declined significantly and the sward became taller in plots receiving high N rates. Only a very few forbs (e.g. Rumex acetosa) maintained or increased their cover with increased N. All Carex species, Juncus species and mosses became less common in plots treated with N, producing an apparently more mesotrophic sward. Short-lived species and low-growing wetland forbs also declined with N rate perhaps due to shading by tall grasses. Legumes were suppressed by high N rates, but were common in plots receiving 25 kg N/ha. Except for grasses, many species common in the experimental site in 1986 declined in cover, particularly in plots receiving high N rates. However, there were no instances of extinction by 1990. The application of 25 kg N/ha encouraged the spread of agriculturally productive grasses within 2 years, while 50 kg N/ha reduced species richness in 3 years.