What Is Soil Composed Of?

Soil consists of approximately 45 percent minerals, 5 percent organic matter, 20 to 30 percent air and 20 to 30 percent water. Soil minerals help keep plants in place while organic matter provides essential nutrients needed by plants for growth.

The solid mineral particles found in soil include sand, silt and clay. Sands are the biggest particles while clays are the smallest particles. Silt particles have a medium size and a fine, smooth texture when dry. Clays typically cluster into a sticky mass when moist and hard clumps dry out, whereas sands have a gritty texture and do not stick to each other. These minerals slowly release nutrients in forms that plants can consume.

Organic matter contains partially decomposed plant and animal remnants as well as organic compounds created during decomposition. Water plays a vital role in delivering various nutrients for plant growth. However, plants cannot acquire all of the water content in soils. The amount of nutrients plants can obtain depends on the size of the plants’ pores and the amount of available water. The rest of the pores contain soil air, which is composed of a gas mixture that is similar to the gases found in the atmosphere.