How Long Does it Take to Form a Layer of Topsoil?

Topsoil

• Topsoil is the uppermost layer of soil, containing a mixture of minerals, micro-biotic and other soil-dwelling life such as worms and crustaceans, and decayed organic material. Generally, the greater the amount of organic material, the richer the soil. Soil that has not been disturbed, such as on a prairie, can have topsoil as deep as several feet. In places where rocks are near the surface, the topsoil may be a thin layer of just a few inches. A desert has little to no topsoil.

Creation

• Topsoil is formed by the plant growth cycle. The roots of the plant break up the soil into smaller bits as the plants grow, allowing for better root growth. After the plants die they lay on the ground and eventually decay, adding their organic material to the soil. This material feeds the soil fauna, which provides more nutrients for further plant growth and leads to bigger, stronger plants with more vigorous roots. The decaying organic material also holds water in place, allowing plants to survive dry periods.

Conditions

• According to West Texas A&M University, topsoil forms at different rates depending upon the material that forms the initial soil, the climate, how the landscape is shaped and the available living material. It is possible that up to a foot of topsoil can be created within 100 years under optimum conditions. Not all topsoil is created equal, though. Rainy areas such as the Amazon have poor topsoil even though it has many decaying plants. The excessive water leaches the nutrients away from the soil, leaving little for plant growth.

Agricultural Concerns

• Poor agricultural techniques can cause erosion or excessive dust, which rapidly cause a loss of topsoil. Farmers have learned the importance of maintaining good topsoil, though. Adding amendments to the soil such as compost and manure mimic nature's topsoil building blocks and replace much that is lost. Leaving the remains of the plants after harvest, such as corn stalks, also help to add more plant material to the soil. Agricultural soil that is properly managed can even gain in topsoil over the years.