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The student’s unpublished data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.
