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Important soil chemistry

Themes: Texture and Structure | Pores and Soil water | Important Soil Chemistry | Quiz

This landscape is shaped by the acid sandy soils. The chemistry of the soil is also very important property as this will determine what will grow and how well it will grow. One of the most important chemical properties of a soil is its acidity or alkalinity, often stated as the pH of the soil. The pH of the soil ranges from about 3 to 8. Below 5.5 the soil is quite acid. Above pH 7 the soil is alkaline. Soil with a pH in the range of 5.5 to 7 tends to be the most flexible and a wide range of plants can thrive within this pH range. Once the pH drops below 5.5, firmly into the acidic range, there is only a limited range of plants that like this level of acidity and can tolerate these acidic conditions. Once the pH is above 7.0, the soil tends to be colonised by a limited range of lime-loving plants.

This beech woodland is growing on a chalky alkaline soil. Soils in wet climates and certainly those developed on acidic rocks, such as granite, will tend to be acid. Soils in high rainfall areas tend to be acid because the rainfall leaches the soil of many of its nutrients which otherwise help to keep the pH higher. Acid soils can be improved by adding lime to soil. This is a common agricultural practice where farm soils need to be maintained at a pH from 5.5 to 7 in order to grow a wide range of crops.

Soils formed in dry climates are often alkaline, i.e., with a pH above 7. Here there is a lack of rainfall to flush the nutrients out of the soil and they stay within the soil. In some dry conditions also evaporation may lead to deep-lying nutrients being brought to the surface. This can lead in some dry-climate soils to excessive amounts of salts being brought into the root zone. In extreme cases this can lead to salinization, in which the soils contain too many salts, which can prevent the growth of many crops.

Themes: Texture and Structure | Pores and Soil water | Important Soil Chemistry | Quiz