Calcium carbonate accumulation layers are formed in the soil, which are maroon or brown respectively, so they are called maroon soil and brown calcareous soil. In the cold climate, a large amount of organic matter provided by grassland plants to the soil for a long time was corroded and accumulated, forming fertile black soil. Soil humus is generally attached to the surface of soil particles, and its dosage is mainly to adjust the depth of soil color. Black soil is generally high in humus, because humus is black and brown.
This is an agricultural proverb, black soil oil, no fertilizer, five grains grow. This proverb actually comes from this. When the humus content is less, the soil is gray or grayish white, similar to gray desert soil, and the color changes from gray to black with the increase of humus content. Purple soil is actually formed by weathering purple sandstone and shale, which is widely distributed in Sichuan and rich in nutrients such as calcium, phosphorus and potassium.
The decisive factors of soil color are mainly the crystalline iron oxide and manganese compounds contained in it, and the color of soil can also be changed. For example, most soils such as gray, grayish white, dark brown and reddish brown are native white soil, red soil and yellow soil. Under the influence of people's cultivation and application of organic fertilizer, the humus in the soil increased and the soil gradually turned black.
Why soil has different colors and what determines the color of soil is explained here today.