To get a representative soil sample, the following steps need to be taken:
1) Collect 3 – 6 small samples, from within the top 6 inches (4 inches for lawns) of the soil, within the area of concern. It is important to take as uniform samples as possible (Example: 2 inch diameter, 6 inches deep). The more small samples that are collected will give a better, more uniform representation of the area. A bulb digger or shovel take very good samples.
2) As samples are collected, mix them together thoroughly in a plastic bucket, as a galvanized or tin bucket can contaminate the soil and cause inaccurate test results.
3) Discard all stones, roots and debris. Transfer about a cup of soil from the small sample plastic bucket to the soil sample boxes provided by the NCDA. Sample boxes and forms are free from the Extension Service.
4) Give each sample box a number or code that will indicate the area sampled, along with your name and address on each box.
5) Fill out the information sheet and bring it, along with your samples, to the local Cooperative Extension Service office.
Reference:
Bailey, Kenny. Importance and Step by Step Instructions for Taking a Soil Test for Homeowners. North Carolina State University Cooperative Extension Service. Retrieved 20 May 2010.