Topsoil is the healthy, fertile layer of soil that lies on top of what are called the soil layer horizons. The topmost soil layer is full of organic matter, is low in salts and high in nutrients, says Utah State University Extension. When an area has lost its topsoil due to erosion or overfarming, topsoil is needed for the area to remain fertile. Choosing and applying the right topsoil is integral to maintaining a healthy place for plants to grow.
Calculate the cubic square feet of topsoil required for your lawn. Measure your lawn and use a topsoil calculator, available on most topsoil vendor websites.
Choose a loamy, debris-free topsoil, suggests Utah State University. Have the soil tested before importing it into your lawn, as soil with too much of one material (sand, clay or silt) will lower fertility and cause problems with planting.
Clear surface rocks and debris off the lawn before laying down topsoil, suggests Arizona Cooperative Extension.
Water the lawn to encourage weeds to grow; then apply a post-emergent herbicide to kill the weeds, suggests the Arizona Cooperative Extension. This keeps the growing area pure. Repeat this after 10 to 14 days; then allow the area to settle and the herbicide to wear off.
Lay down a 6- to 8-inch layer of topsoil onto the lawn and incorporate it using a rototiller device, says the University of California. Smooth out the area using a rake or yard roller filled halfway with water to smooth out the area.