top soil

     

Top Soil is the upper, outermost layer of soil, usually the top 2 to 8 inches. It has the highest concentration of organic matter an microorganisms, and is where most of the Earth's biological soil activity occurs. Plants generally concentrate their roots in, and obtain most of their nutrients from this layer. The actual depth of the topsoil layer can be measured as the depth from the surface to the first densely packed soil layer known as hardpan.