Illinois Soil Testing Association (ISTA) services

A soil test is only as good as the sample provided to the testing lab. Generally, a subsample should be taken from the layer of the soil from the surface to 7 inches  eep. Three to five subsamples should be collected from 3 to 10 acres. Because of soil variations, taking too few samples by subsampling too large an area may not give an accurate fertility map of the field. Remember, sampling is the most critical part of soil testing.