The layer of uppermost soil called topsoil is the focus of attention of many soil scientists worldwide, according to U.S. Department of Agriculture scientist Ron Myhrum. Healthy, fertile topsoil is necessary to sustain agriculture. Eroded topsoil leaves farmland that has no microbial activity and turns to lifeless dust. New methods called "no-till" help regrow topsoil.
Soil's top layer is called the "A Horizon" layer, according to the USDA's Soil Survey Manual. Topsoil is measured as the depth from the top to the subsoil. It is 2 to 5 inches deep and is the area where the most biological activity takes place. Plants are fed and grow in this layer. Topsoil is the soil layer most affected by erosion problems.
Topsoil layers are a living community rather than an inert substance. Topsoil feeds and sustains plant life. Earthworms, fungi, protozoa, small mammals, bacteria, and small algae live in fertile topsoil. These organisms reproduce constantly, providing nutrients for the crops that grow on the soil. Keeping soil alive with microorganisms is the goal of topsoil management and enrichment.
According to the National Sustainable Agricultural Information Service, fertile topsoil soaks up water easily, is crumbly to the touch, resists erosion and nutrient loss, stores moisture for drought periods, does not require increasing input for high yields, and produces healthy, high-quality crops.
Fertile topsoil is the key to sustainable agriculture. Topsoil erosion creates land that does not produce food well. Soil scientist John Reganold of Washington State University says, "Globally, we are eroding soils at a rate much faster than they can form." According to the National Academy of Sciences, cropland in the United States is being eroded 10 times faster than it can be replaced. Topsoil grows back at a rate of 1 or 2 inches every hundred years.
The "no-till" method of topsoil management is recommended as a solution and prevention to losing valuable layers of topsoil. This method stresses not tilling the land between plantings, leaving crop stubble to prevent erosion, and planting new seeds between the stubble rows. Constant replacement of soil with organic matter is also recommended. Topsoil layers can be regenerated through the biological activity of the microorganisms in compost.