Dirt and soil are NOT the same. Dirt is the stuff we tracked through the kitchen as kids. SOIL is the one stop shopping of the plant kingdom. It anchors the roots, stores the nutrients and allows the oxygen and water to be present. It is composed of air, water, minerals, organic matter and living organisms.
Sandy soils allow for plants to take root quicker, but water and nutrients can pass through quickly.
Clay soils will retain nutrients and water, but sometimes in excessive amounts and rob the soil of oxygen. A silty soil, a blending of the two, is the optimal for plant health. By amending with soil with organic matter. Feeding your soil is as important and probably MORE important, than feeding your plants. This is NOT to say feeding your plants is a bad idea, far from it.