Many courses apply sand to fairways to improve the physical characteristics of the rootzone and dilute thatch and organic matter. In this article, I will share research conducted in an athletic field setting that has implications for topdressing golf course fairways.
A study completed in 2008 and published in 2010 – “Sand Topdressing Applications Improve Shear Strength and Turfgrass Density on Trafficked Athletic Fields” – evaluated cumulative sand topdressing rates of 0, 0.5, 1, 1.5 or 2 inches in one season applied from July 11 through August 15 in 2007 and repeated the process in 2008. Topdressing was applied at a 0.25-inch depth during each event. The native soil was a compacted sandy loam with a high bulk density of 1.6 grams per cubic centimeter and a low infiltration rate of only 0.12 inches per hour. The sand applied for topdressing was a well-graded material – meaning it had a fairly equal proportion of different sand particle sizes – comprised of 90% sand, 7% silt and 3% clay. The coefficient of uniformity (CU) of the sand was 8.0, which confirms the wide particle size distribution, and the infiltration rate was 6.1 inches per hour. As a reference, the recommended CU range for putting green construction sand is 1.8 to 3.5. The sand used in this study was not the typical coarsely graded sand often used to topdress golf course fairways.
Research plots were subjected to simulated traffic. The measures of performance in this study focused on turfgrass cover, the number of turf shoots per square foot and surface strength called turf shear, measured with the Clegg turf shear tester which measures divot resistance.
Sand Topdressing Proved Highly Beneficial
After two years of study, sand topdressing at a rate of 0.5 inches per year – in 0.25-inch applications – for a cumulative total of 1 inch of added sand resulted in the best performance of all treatments as measured by a combination of turfgrass cover, shoot density and shear strength. Turfgrass cover, shoot density and shear strength increased for all treatments in year two, including the non-topdressed plots, but the shoot density in the topdressed plots increased by 228%, far surpassing the increase in control plots. Shear strength (divot resistance) was highest in year two in the untreated plots. Of the sand topdressed plots, the 0.5 inch per year program yielded the highest value.
The researchers concluded that the higher shear strength in the non-topdressed plots was due to the measurement interacting with the highly compacted sandy loam soil. In this case, the higher shear strength was not indicative of a positive characteristic, but rather a representation of the compacted soil with lower turf shoot density – about half the density of the sand topdressed plots – and lower turfgrass cover. Also of note is that although the heavier sand applications showed equally good turfgrass cover and slightly higher shoot density than the 0.5 inch per year treatment, they resulted in lower turf shear strength. The study shows that some sand is good, but a lot of sand will destabilize the surface. On a golf course fairway, this means higher risk of damage from golf cart traffic and softer playing conditions.
The overarching message from this study is that sand topdressing may be a good practice for golf course fairways and approaches if rates are limited to about 0.5 inches per year with split applications, which amounts to approximately 80-90 tons per acre per year. Additionally, the sand in this study encouraged a firmer surface due to the widely graded particle size distribution. If you are using a coarse sand that is narrowly graded, the firmness will not be as great and more sand will further destabilize the surface.
West Region Agronomists:
Brian Whitlark, senior consulting agronomist – bwhitlark@usga.org
Cory Isom, agronomist – cisom@usga.org