Soil sampling for turfgrasses should be confined to the top four inches of soil.

Soil sampling for turfgrasses should be confined to the top four inches of soil.

• A. True
• B. Only top two inches
• C. Top six inches
• D. Top four inches

Answer: (D)

Most turfgrass roots stay in the upper portion of the soil, so soil tests should target the zone where they actually take up nutrients. Sampling the top four inches captures the soil properties that most affect turf growth—pH and available elements in the root zone—without being skewed by deeper subsoil that the grass doesn’t use as much. Sampling much deeper could blend different fertility and structure from the subsoil, giving results that don’t reflect what the turf needs. Sampling too shallowly, like the top two inches, can overemphasize recent surface amendments or thatch rather than the root zone. For these reasons, four inches is the standard depth for turfgrass soil testing.