Soil Nutrient Variability in Southern Piedmont Soils
When sampling soil, it is usually recommended that one collect a small amount of soil from a number of locations within a field, then mix the soil together in a pail for a good, representative sample. The reasoning behind this approach is that soil nutrient level tends to vary across a field due to the heterogenous nature of soil.
The link address is: http://www.ext.vt.edu/news/periodicals/cses/1996-10/1996-10-01.html