Comparing Surface Firmness Measurements on Sand-Based Putting Greens.

For golf course putting greens, surface firmness is an important component of performance and overall quality. As incoming shots land on the green, firmness plays a critical role in where the ball ultimately comes to rest, as well as the resulting condition of the putting surface. While various devices exist for quantifying firmness of turfgrass surfaces, there is a need for greater context when interpreting such measurements. For golf course superintendents charged with the dual, and at times, competing responsibilities of managing long-term plant health along with optimizing performance of the putting surface, firmness is a desirable attribute; yet management practices for achieving consistent, high-quality greens are often aimed at addressing underlying factors influencing firmness, particularly volumetric water content (VWC) and organic matter (OM). An inverse relationship between VWC and firmness is generally accepted, however, the extent to which firmness and VWC measurements provide unique, independent information, and contribute to turfgrass management decisions needs further investigation. The objective of this research was to examine the correlation of firmness measurements to i) ground truth data regarding VWC and OM, as well as ii) golf ball/putting green interactions (such as ball bounce and impact damage). Putting green firmness was measured using both the FieldScout TruFirm Turf Firmness Meter (Spectrum Technologies), and Clegg Impact Soil Tester (Lafayette Instruments). In situ measurements for VWC were obtained at 1.2, 2.5, and 3.8 cm depths, using the FieldScout TDR350 and Turf Rod Spacer (Spectrum Technologies). Destructive sampling methods produced ground truth values for VWC and OM. Digital image analysis was used to quantify severity of golf ball impact. A highly significant linear relationship was observed between firmness measurements of both devices and VWC at all depths. For the TruFirm, maximum R² value of 0.72 indicated a limited ability to manage putting green firmness exclusively through moisture.