Agriculture in The United Kingdom - Land

Land

Soil is a complex mix of mineral and organic components, produced when rock is weathered and acted on by living organisms. Most British soils are 2% to 5% organic and 95% to 98% mineral, but soils such as peat may contain up to 50% organic matter. In the British Isles as far south as the Thames Valley, the soil has been heavily glaciated, which not only ground down the rock but redistributed the resulting matter. As a result, most British soils date from the last Ice Age and are comparatively young, but in level areas and particularly south of the Thames Valley, there are much older soils.

Many British soils are quite acidic, and a large proportion of British farm land needs repeated applications of alkalines (traditionally lime) to remain fertile. Nitrites are soluble, so rain rapidly carries them away. Acid rain increases soil acidity, but even normal rain tends to be slightly acid, increasing the natural acidity of British soil. Rainfall in Britain exceeds the rate of evaporation. This means that in freely drained areas, soil base material is washed away, which leads to a higher concentration of organic acids in the ground. This relatively high soil acidity is one of the factors that lead to liming. Lime tends to counteract soil acidity, and with fine particulate soils such as clays, also encourages the formation of a better soil crumb structure that will aerate and help with drainage. Its benefits have been known, if not scientifically understood, since Roman times.

Soffe (2003) summarises the acidity of British soils as follows:-

Land type	pH
Sandy heath land	3.5-5.0
Calcareous (chalky) brown soil	6.5-8.0
Upland peat	3.5-4.5
Cultivated soil, non-calcareous	5.0-7.0
Cultivated soil, calcareous	7.0-8.0
Permanent pasture, lowland	5.0-6.0
Permanent pasture, upland	4.5-5.5
Lowland peat	4.0-7.0

Owing to high rainfall in the UK, less freely drained areas tend to become waterlogged. Wet land may be unable to bear a tractor's weight, and drainage makes soil lighter and more easily worked, improves crops' ability to absorb food because there is more root surface area, stimulates helpful micro-organisms and allows accumulated poisons to be carried away. In Britain field drains are traditionally open ditches, but increasingly, covered pipes have been used in more modern times. Earthworms are important for creating small drainage channels in the soil and helping to move soil particles.

No appreciable plant growth takes place at temperatures below 4°C. The growth rate increases as temperature rises, up to a maximum limit which is of no relevance to the British Isles. Dark soils tend to absorb more heat, and are therefore preferred.

As crops grow, they absorb nutrients from the soil, so land fertility degrades over time. However, if organic matter poor in nitrogen but rich in carbohydrate is added to the soil, nitrogen is assimilated and fixed. Fertility increases while land is under grass, which helps to accumulate organic matter in the soil. These factors mean that soil is traditionally improved by means of liming, draining, and allowing to lie fallow. It is traditionally fertilised with manure, nitrogen, phosphates, and potash.