Fields with cool season perennials should be sampled in July or August. Fields with warm season perennials should be sampled in January or February. Fields for growing hay crops should be sampled every year and grazed pasture fields should be sampled every three years. The intensity of land use will dictate the sampling schedule. Sample the soil several months before establishing perennial pastures to allow ample time for the lime to react with the soil.
Separate the fields according to soil types, cropping history, erosion and past management practices. Follow a random zig-zag pattern over the field and avoid areas of nutrient concentration such as near watering areas and shady spots.
One composite sample of 15 to 20 cores is generally recommended for each 10-15 acres.
The soil should be sampled to the plow depth before seeding and to a depth of 4 inches after establishment. This is helpful in monitoring surface soil acidification and nutrient depletion. Periodic deeper sampling to the root depth will help monitor subsoil levels of the more mobile nutrients such as potassium and prevent over-fertilization.
In all situations, it is imperative to use clean sampling tools. Pesticide or fertilizer residues on the sampling device as well as the container used for mixing cores will create misleading results.