Photo by Daniel O’Brien
Firmness is an important attribute of healthy putting greens, affecting both playability and durability, but it is often discussed in subjective terms (“want firmer greens” or “greens are too soft,” for instance).
Underlying factors associated with firmness include volumetric water content (VWC), organic matter (OM) and bulk density (BD), and these are managed through irrigation, aerification, topdressing, verticutting and rolling. Understanding the extent to which measurements reflect each of these underlying factors may allow superintendents to improve the efficiency and precision with which they manage firmness.
This research sought to examine the relationships between firmness measurements and ground-truth data for VWC, OM and BD, and to compare variability among measurement devices.
The experimental area was a Penn A-1 creeping bentgrass green with a USGA sand-based root zone. Measurements were taken using the Clegg Impact Soil Tester (Lafayette Instruments), FieldScout TruFirm turf firmness meter (Spectrum Technologies) and FieldScout TDR 350 moisture meter (Spectrum Technologies). Combinations of irrigation, rolling and cultural practices were used to create individual plots. Samples were extracted at the site of each measurement to calculate ground-truth VWC, OM and BD. Device comparisons were based on 24 adjacent measurements within plots.
All devices had significant relationships with VWC, OM and BD. The TDR 350 had the strongest correlation with VWC; across all devices, OM had the weakest correlations; and TruFirm was correlated most closely with BD.
These results indicate that superintendents implementing proper maintenance practices should consider the different capabilities and limitations of devices used to measure firmness.
— Daniel P. O’Brien; Douglas E. Karcher, Ph.D.; and Michael D. Richardson, Ph.D., University of Arkansas, Fayetteville, Ark.
More on this research:
Comparing surface firmness measurements on sand-based putting greens (PDF)
New Technologies for Evaluating Putting Green Surface Characteristics (PDF)
Teresa Carson is GCM’s science editor.