The acidity of Welsh soils

Abstract. The pH of soil surface horizons in Wales ranges from 3.5 to 7.5 and is significantly higher on agricultural land than under either rough grazing, unenclosed grassland or woodland. Sufficient information exists to map broad classes of soil pH. Rough grazing and woodland sites are concentrated on soil types which are naturally very acid. In Wales, such soils are found on the main mountain ranges and show up clearly on the map of pH. Their acidity is the result of an interrelationship between soil, climate and vegetation. However, afforestation, particularly with coniferous species, appears to lower the pH of the underlying soil. There is a trend in agricultural soils towards lower pH under a moister climate.