Even in small amounts, organic matter is very important. This fact sheet answers some basic questions about soil organic matter. Partially decayed plant material and microbes, for instance, plant material you mix in or manure. The stable material formed from decomposed plants and microbes. This material is called humus, and is broken down very slowly.
Organic matter affects both chemical and physical properties of the soil.
If CEC is increased, the soil can hold more nutrients and release them for plant growth. To increase CEC, you have to increase organic matter. Organic matter loosens the soil, which increases the amount of pore space. This has several important effects. This means that the sand, silt and clay particles in the soil stick together, forming aggregates or crumbs.