Category:United Kingdom Soils
Britain has a very varied climate and geology which has led to a wide range of soils being developed. The annual rainfall varies from about 250mm in East Anglia to over 2,000mm on the top of Mount Snowdon in North Wales. Furthermore, there are significantly higher annual temperatures in Southern England than in the north of Scotland and this affects the rate of weathering of rock to form soils. Geologically, the rocks of Britain, which form the parent material of soils, are also very varied both in age and in type. Britain has examples of rocks and other geological deposits from the Pre-Cambrian, from 2,000,000,000 years old (that's 2 billion years!) through to those formed during the Ice Age (about 1 million years ago) and other more recent deposits. This diversity in climate and geology has led to over 700 different types of soil recognised in Britain. The vegetation also influences the way soils form. Since the last Ice Age, when soils have began to re-form after being scoured away, there have been many changes in vegetation. As the temperatures warmed up after the Ice Age, so different types of vegetation colonised the soils, each making its mark on soil formation. One of the more recent colonisations was that of deciduous woodland which covered much of Britain except the higher mountains. Under this vegetation the brown earth soil, one of the main soil types of Britain, became widespread In the last 250 years in particular, humans have had a major effect on the soils of Britain. Much of the deciduous forest was cut down in the 16th to the 18th centuries and the land ploughed to make way for agriculture. Since deforestation much of the land has been cultivated. In recent years there has been intensification of agriculture, with more extensive and sophisticated mechanisation, much increased use of fertiliser, and extended use of pesticides and herbicides. Humans are now having a large part to play in soil development. There are two main soil groups covering over 60 per cent of the country. These are 'brown earths' and 'gley' soils. In many ways the brown earths can be considered as the type soil to form under the temperate climate of Britain. Brown earths are generally well or moderately well drained soils, moderately deep (usually 50-150 cm deep) with brownish horizons below the topsoil. The brownish horizons result from the weathering and release of iron oxides in the temperate climate. Gley soils are soils which are periodically waterlogged. There are two main types of gley soil: surface water gley and ground water gley. Surface water gley soils are formed in slowly permeable sediments such as clay strata from several of the geological periods or in clayey glacial deposits left at the end of the last Ice Age. The key feature of the soils is that their B horizon is quite compact and contains few large pores when moist. When it rains, particularly in winter, there is often more water entering the soil than there are pores capable of transporting it through the soil and the soil becomes anaerobic. This leads to waterlogging in the soil and a consequent lack of aeration. The groundwater gley, by comparison, occurs on sediments in low lying areas, such as river floodplains. Here during the winter and spring the water table rises up into the soil and floods the soil horizons. This process also leads to the soil being periodically anaerobic with grey colours and occasional mottles of reddish/brownish iron oxide as evidence. In addition to these two extensive types of gley soil, there is also the less extensive unripened gley soil formed on land that is regularly flooded by water, such as tidal sea and brackish water Another distinctive soil of Britain is the Podzol. These soils are formed on lighter textured material like sands and gravels, under coniferous forest and heathland. They are generally strongly acid and normally well drained. Under the acid conditions there is build up of organic remains at the surface. Rainwater reaching the soil becomes acidified and is able to leach some of the nutrients and transfer them from the upper to the lower parts of the soil profile. The soils thus have dark brown or black surface layer, below which is a whitish bleached horizon from which nutrients have been washed out, then further down are layers where organic matter, iron and aluminium washed down from above are redeposited. It is one of the more colourful and distinctive soil profiles of Britain. There are ten major groups of soils in Britain of which four of the most extensive have been described in the previous section. The remaining six cover about forty percent of the country. One of the most interesting of these is the group of organic soils, in which most of the profile depth is composed of organic matter. These are soils which are dominantly formed of organic matter. Some of these soils occupy areas of lowland Britain where they form some of the most fertile soils in the country. One of the main areas of these highly fertile soils is the Fenlands of East Anglia where there are several metres thickness of peat. Organic soils of this major group can also occur in the upland areas where high rainfall and acid conditions mean that over centuries the organic matter has been slow to break down and now exceeds 50 cm in thickness. Unlike the fenland soils these upland soils are very acid and largely unproductive. Another fairly widespread major group of soils is the pelosol. These are soils formed on the clay deposits of Britain but with rather better drainage than that found in the gley soils. They have brownish or reddish B horizons (depending on the clay strata from which they are formed). Britain also has numerous examples of thin, little-developed soils, formed on the steep slopes of the uplands or in other unstable situations such as sand dunes. These soils are termed lithomorphic soils. These soils lack a B horizon; instead they have an A horizon immediately overlying the C horizon. Such soils formed on calcareous rocks such as chalk are termed rendzinas and those on acid rocks, rankers. In a small country with a relatively large population like Britain it is not surprising that humans have altered some of the soils. There is therefore a group of man-made soils. These are soils which have been extensively changed by humans, to a greater extent than by everyday farming. These soils are of very mixed origin. Some have been greatly influenced by building as in the towns and cities. Others are related to reclamation after mining, as in the areas of coal mining. They have very mixed profiles and the profiles do not result from the natural soil forming processes like those in the other major soils above.
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