Dr. Jim Crum and Dr. Trey Rogers
Nearly twenty years ago we initiated research to determine the engineering and agronomic properties of high-sand content root zones used in golf putting greens, athletic fields, and as topdressings to these surfaces. We found to increase the strength and stability of surfaces it was necessary for the sand to have a wide distribution of sand particle sizes; including relatively significant proportions (up to 25%) of Very Coarse and Coarse sand (0.5 – 2.0 mm). Sands of uniform size exhibit poor strength and stability because there are few particles of smaller size to fill the voids surrounding the sand particles and increasing surface friction and strength.
A recent article in the Green Section Record by Dr. James Murphy of Rutgers University suggests when a sand containing Very Coarse and Coarse sand sizes is topdressed to particularly dense turf, these larger particles remain on the surface, interfere with mowing and play, and need to be removed (http://tinyurl.com/pa5cxdv) (Murphy, 2007). This implies the larger particles are not being incorporated into the plant canopy and are a deterrent. A number of years ago an internship student completed an Independent Study at the golf course he was working where he collected the sand removed by the mowers following topdressing. He and the superintendent wanted to know if the larger particles were being preferentially removed with mowing and leaving mainly the finer particle behind. If that was the case, why not just apply the finer sand and not deal with the problems associated with larger particles. The student’s unpublished data clearly suggested the particle-size distribution of the sand collected in the mower buckets was similar to the sand that was applied. They concluded to continue to apply the wide-distribution sand even though more maintenance to bed-knifes and reels of mowers would be required.
Recently, Mavis Consulting, Ltd released an article where they measured the amount and sizes of sands removed with mowing following topdressing. Go to http://www.mavisconsulting.com/articles and look at the 2013 Sand Top-dressing article, if interested. Their findings were similar to those found by the internship student; the sand removed with mowing is similar to that which was applied.
The article from Rutgers suggests alleviating the problem of topdressing with sand containing the larger particles, topdress with a finer sand during the season and then following core cultivation use coarser sand to topdress and fill the cultivation holes. Filling the core cultivation holes with the coarser sand would continue the connection of larger pores from the surface into the root zone and bypass layering issues. During the length of their study they have not seen or measured negative effects of using the two materials. Why might using these kinds of materials raise concerns? There are many reasons to topdress turf surfaces, but diluting the accumulation of organic matter that creates a layer with smaller pores is probably the most important. Discontinuities in materials that create different pore sizes have caused problems for years. A layer of smaller pores lying above a layer of larger pores creates water-flow problems creating a near-surface layer holding more water and less oxygen.
Even though Dr. Murphy has not seen any short-term negative effects of using two sands, it is our opinion not enough work has been done to determine the long-term effects of this practice. We suggest, and believe, for the long-term health of these turf surfaces it is important to continue to use the same wide-distribution sands to topdress. Yes, it will create more mower maintenance. But for now we believe it is the best practice to follow.