Topsoil is the uppermost 8 to 12 inches of soil and is considered the most productive layer of Earth. It can take natural processes more than 500 years to create 1 inch of topsoil, making it a vital natural resource. Topsoil is made of varying amounts of living and dead organisms, minerals and nutrients. Different size mineral particles create the different types of topsoil: clay, sandy and loam.
Clay topsoil has the smallest size soil particles, which bind together to create a dense structure. It is made of finely grained minerals that have been formed over time by the weathering process on rocks. Clay topsoil contains organic matter and has nutrient content, but contains little sand. The dense structure makes it difficult for water to drain easily. Water retention in dense clay topsoil can cause root rot in growing plants. Water also pools on the soil surface. In home gardens, clay soil can be amended by adding organic compost to give it a more pliable structure.
Sandy soil contains large amounts of weathered rock particles such as quartz, granite, shale and limestone. Roots have a difficult time holding to sandy soil because soil particles are not big enough for root hairs to cling to. It also drains very quickly and does not retain nutrients. Sandy soil is easily washed away by wind and rain. Organic matter added to sandy soil improves its structure. Organic matter helps create larger soil particles and adds nutrients.
Garden loam is an ideal soil. It has a balanced mixture of clay, silt and sand that hold its structure easily. Loam topsoil allows roots to spread while also retaining water and nutrients. Topsoil without good structure erodes easily. Healthy loam topsoil is created by good soil conservation habits such as replacing organic content and no-till agriculture.
Topsoil erosion is a global problem because topsoil is eroding faster than it is being replaced, according to the Center for Earth Leadership. Topsoil is the source of nutrients for food crops.