From Just Food:

Did you know that dirt and soil are not the same thing?

Soil is a complicated system of air, water, minerals, organic matter and living organisms (an acre of healthy topsoil can contain 900 pounds of worms!). Healthy soils which have a balance of all of these elements provide the nutrients that plants need to grow well and to resist weather, pest and disease stress. Your CSA farmer invests a lot of effort in creating and maintaining healthy soil so that they do not lose their topsoil or need to use chemical fertilizers which can damage their land, contaminate water sources and end up on your food. They use a mix of techniques to keep their soil healthy including reduced plowing (tillage), crop rotation, adding compost and/or manure and using wind breaks to minimize erosion. For more information go to The Sustainable Table, and for a great interactive resource on soil for kids go to The Discovery School.