The soil color is an important diagnostic feature that provides information about the humus content, the availability of oxygen and the iron compounds in a soil . The soil color is one of the easiest criteria for assessing soil types . The soil color is differentiated on the one hand by the hue (as black, red-brown or yellow), on the other hand by the color saturation and color depth (e.g. as deep brown) and the color brightness (black and white components, pale or gray-brown). In soil science, the Munsell color system is used to determine the color . The decisive factor for the soil color is the soil's content of organic substances and various iron and manganese compounds . Typical color-coded soil characteristics are:
- A general rule (which does not apply in all cases) is that dark soils are more fertile than lighter ones. The dark soil color mostly results from the presence of a large amount of humus . Every now and then, dark brown or black floors owe their color to mineral materials or increased moisture. In such cases, the dark soil color is not a sign of fertility .
- The soil color often leads to characteristic soil names such as black earth or podsol (bleaching earth).
- Almost all yellow or yellowish soils are less fertile. They owe their color to reduced iron compounds. These soils are therefore a sign of poorly drained land.
- Soils with a red or reddish-brown hue contain a greater proportion of iron oxides (which result from the parent rock) that have not been exposed to excessive moisture. The red color of a soil is therefore generally an indication that the soil is well drained, not excessively moist, but fertile. In most regions, the reddish color of the soil may be the result of newly formed minerals that the plants cannot use.
- Greyish soils may lack iron or oxygen, or they may have an excess of lime . The transition from the colored color (oxidation zone) to the grayish color (reduction zone, see Gley ) shows the mean groundwater level.