Many producers think that they should take a sub-sample of every kind of soil in a field. That isn’t the way to do it. Sub-samples should be taken from areas within a field that are similar. If there are areas that differ substantially from the majority of soil in the field, they should be sampled separately.
One of our soil scientists showed how important it is to get representative samples by conducting some tests this summer. He collected acid and neutral pH soils from clay, silt loam and sandy soil types. They mixed two soils at a time in different proportions (Example: 9 parts acid sand soil and 1 part basic clay soil; 8 parts acid sand soil and 2 parts basic clay soil ... and so on).
They found that the strong buffering capacity of clay soil dominates pH measurements in a composite sample. Even when only 10% of the soil in a sample was clay, the pH reading was heavily weighed towards the clay. Take representative, not average, soil samples.