In fields with a history of banded fertilizer applications, the recommended number of cores per sample area increases to what range?

• A. 20-25 cores.
• B. 5-8 cores.
• C. 12-18 cores.
• D. 30-40 cores.

Answer: (A)

Fields with banded fertilizer are not uniform; nutrient levels are concentrated along the bands and depleted between them. To obtain a representative soil test, you must sample enough locations so the results reflect the whole area, not just a single band. Increasing cores per sample area to about twenty to twenty-five cores captures multiple bands and the spaces between them, providing a more accurate composite picture of the field’s average nutrient status. If you take too few cores, the result can be biased toward the more nutrient-rich or more depleted zones, which can lead to over- or under-fertilization in practice. Spreading out the sampling across the field helps create a composite sample that truly averages the variability. The other ranges either under-capture the variability or add unnecessary effort without a meaningful gain in accuracy.