Healthy food grows in healthy topsoil. Topsoil is the upper 2 to 8 inches of soil where plant root systems receive their nutrients for growth. It takes natural earth processes 500 years to create 1 inch of topsoil. Topsoil conservation and renewal is an important aspect of organic farming and sustainable agricultural practices worldwide. Topsoil erosion can cause soil depletion, crop failure and, ultimately, famine.
Topsoil is the layer formed from rocks and decaying organic matter, which consists of plants and animals. It is 45 percent minerals, 25 percent water, 25 percent air and 5 percent organic matter. The health of the layers of topsoil is responsible for the health of the food grown on it. Nutrient content of topsoil is mirrored in the nutrient content of food. Topsoil is the most important part of soil for food production.
The topsoil layer is where biological activity takes place; it is a living community of organisms. Earthworms, fungi and many species of bacteria are active in topsoil in close proximity to plant root systems. These life forms act as reservoirs of nutrients that are released into root systems. Topsoil that has been overexposed to chemical fertilizers loses its biological activity and, therefore, its nutrient content.
A healthy topsoil layer is soft, crumbly, drains easily, supports high populations of microorganisms and stores water, according to the National Sustainable Agriculture Information. Good topsoil also has a rich, earthy smell and does not require increasing inputs for crops to grow well. It resists erosion, soaks up rain with little runoff and retains nutrients. Healthy topsoil also does not crust after planting and has few clods.
Natural topsoil in forests and grassland produces plants and animals without tillage and without the addition of fertilizer. Understanding the way natural topsoil is built and functions helps to explain how healthy garden topsoil can be built. Sustainable agriculture methods and organic gardening reproduce natural methods in farmland topsoil management.
The layers of topsoil in a home garden are important because soil health creates plant health. Topsoil is healthy when it has high organic content that feeds nutrients into the soil and the root systems of vegetables. Organic content is fed into the topsoil by adding compost. In large-scale farming, organic matter is added to the topsoil by practicing the "no till method," growing cover crops and adding compost.