Several research studies published between 2000 and 2011 have documented various advantages with regular applications of sand to putting greens. These benefits include increased surface firmness, increased green speed, increased infiltration and a decrease
in organic matter content in perhaps a “dilution-is-the-solution” approach. Sand typically is applied via backfilling of cultivation (i.e., aeration) holes and grooves, injection, drill-and-fill and topdressing. Too much added sand, however,
may contribute to surface instability and poor root-zone moisture and nutrient retention and/or availability.
A common recommendation since the early 2000s was to maintain < 3-to-4% organic matter (OM) within the putting green’s upper root zone. This may be achieved by only affecting 15% to 20% of the surface area each year with core cultivation and
incorporating 40 to 50 cubic feet of sand per 1,000 square feet (0.011 to 0.015 cubic meters per square meter) per year.
Researchers at Delaware Valley University (Doylestown, Pa.) wanted to benchmark OM content of putting greens in eastern Pennsylvania, in close proximity to the university. The term benchmark refers to a standard or point of reference to compare against
data acquired in the future. From 2016 to 2021, putting greens were sampled during July and August. A total of 221 putting greens were included in the study, comprising 104 USGA spec, 91 sand-capped and 26 California construction type. For all 221
putting greens, the average creeping bentgrass cover was 65%, with a range of 1%-100% creeping bentgrass cover, with annual bluegrass representing the other turfgrass species.
At each golf course location, soil samples were obtained from their best, average and worst performing greens determined by the golf course superintendent. Eight cores of 0.75 inch (1.91 centimeters) diameter were extracted in a uniform pattern at each
putting green. The cores were divided into 0-1, 1-2, 2-3 and 3-4 inches (0-2.5, 2.5-5.1, 5.1-7.6 and 7.6-10.2 centimeters) thus representing eight samples per depth for each putting green. With each soil core, the turfgrass verdure was removed, but
the thatch and mat remained with the core. The OM percentage was measured in the laboratory by the loss-on-ignition method.
Soil samples for all 221 putting greens revealed an overall average OM per depth as follows: 0-1 inch = 2.8% (range of 0.6% to 10.8%); 1-2 inch = 1.8% (range of 0.4% to 5.9%); 2-3 inch = 1.5% (range of 0% to 6.3%); and 3-4 inch = 1.6% (range of 0% to
7.4%). Specifically looking at the 0-1-inch depth for each putting green type, average OM for USGA-spec greens = 2.7% (range of 0.6% to 10.4%), sand-capped = 3.2% (range of 1.2% to 10.8%), and California = 1.9% (range of 1.0% to 2.8%).
So, is there an “ideal” OM amount for golf course putting greens in this particular mid-Atlantic region? At the 0-1-inch depth, 42 of 221 (19%) of those putting greens had ≥ 4% OM, 25 of 221 (11%) had 3%-4% OM, and 154 of 221 (70%) had
< 3%-4% OM threshold, which meets the contemporary guidelines for OM in the upper root zone. But one size does not fit all, as there are instances where some putting greens might perform well at one OM level, while others experience problems, and
therefore OM laboratory data should not be the only factor guiding agronomic management programs.
Other parameters were measured during this study. For example, for all 221 putting greens, the average sand applied was 15 cubic feet per 1,000 square feet (0.004 cubic meter per square meter) per year (range of 1 to 67 cubic feet [0.0002 to 0.018 cubic
meters]). Of note, a common practice in this geographic region between 1970 and 1990 was topdressing with “dirty sand” (i.e., 6/2/2 sand/soil/peat), but since the 1990s, pure sand and kiln-dried sand have become the most common materials
used.
The take-home message with this research is that measuring OM in putting greens (i.e., benchmarking) should become an important part of an agronomic maintenance program, so that the various cultural practices can be evaluated over time for their influence
on OM. In the end, it is a matter of measuring, monitoring and modifying organic matter to produce a putting green surface with the desired aesthetics and function.
Source: Linde, D.T., A.D. Mitchell and B. Hannan. 2022. Benchmarking putting green organic matter in eastern Pennsylvania. Crop, Forage and Turfgrass Management 8(1):e20163 (https://doi.org/10.1002/cft2.20163).
Mike Fidanza, Ph.D., is a professor of plant and soil science in the Division of Science, Berks Campus, at Pennsylvania State University in Reading, Pa. He is a 22-year member of GCSAA.