PO 16. Recognize how the following affect soil sampling methods.

Anything that induces variability in the field will increase the amount of sub-samples that must be taken.  This reduces the likelihood that the results of a given composite sample will be skewed by a sub-sample taken from a non-representative area of the field.

The method of previous fertilizer application can change the nutrient profile of a field.  Banding fertilizer and manure spreading are known to increase spatial variability within a field.  As not all areas receive the same amount of fertilizer or manure, the nutrient availability differs throughout the field.  The more variability there is, the more sub-samples should be taken.  If the location of the fertilizer bands is known, samples should NOT be taken directly from the band.

Tillage systems impact the distribution of nutrients over a field and over depth.  Deep tillage, zone tillage, etc. will differ in thoroughness of mixing and thus in nutrient variability.  The more tillage there is, the less variable the nutrient distribution, and the minimum recommended sub-sampling guidelines can be followed.

Nutrient stratification, or irregularities in where nutrients are located throughout the soil profile, is influenced primarily by tillage.  In no-till situations, nutrient stratification is usually greater than for conventionally tilled fields.  Consistent sampling to the recommended depth is critical.  For soil pH in no-till systems, two soil samples will be needed: 0-1 inch (for seeding), and 1-6 inches.  If the surface sample pH is lower than 6, a limestone application should be made, even if the deeper sample does not call for liming.