Which soil type is richest in organic matter?

In a typical soil profile, the topsoil layer is richest in organic matter because it contains decomposed plant and animal material called humus. This layer supports most root growth, microbial life, and nutrient cycling. The amount of organic matter varies widely depending on climate, vegetation, and land use, but well-developed topsoil is far more fertile than deeper layers. Agricultural practices can either build up or deplete this valuable layer. Soil scientists treat topsoil conservation as essential for long-term food production.