is bulk density the answer? - PACE Turf

PACE INSIGHTS January, 2001 Volume 7 Number 1 page 4
interested in learning how two different aerification
procedures affected soil compaction on putting greens.
1. Shallow (3” deep) core aerification (with cores
removed) with 5/8” tines.
2. Deep vertidraining (9 inches deep) with ¾” tines.
In both cases, the holes were filled with 20-30 silica
sand. One day later, we took penetrometer readings at
8 different soil depths, and from three locations: the
sand-filled aerification holes, the sand-filled vertidrain
holes, and the non-aerified area between holes.
Figure 1. The effect of aerification procedures on soil
compaction, when readings were taken with a cone
penetrometer, 1 day after aerification, topdressing and
irrigation. Candlewood Country Club, Whittier, CA.
Compaction values higher than 300 psi are considered
unacceptable for optimum plant growth.
Compaction (psi)
700
600
500
400
300
200
100
0
between holes
aeration holes
vertidrain holes
unacceptable
acceptable
1 2 3 4 5 6 7 8
Soil depth (inches)
To summarize what we found:
• The cone penetrometer provided a good estimate of
soil compaction. However, if the area to be
sampled is too narrow or too shallow, readings may
not be accurate (see below).
• As expected, the areas between aerification holes
were the most compacted, with acceptably low
compaction readings only at the 1 and 2 inch soil
depths. At depths of 3 inches and higher, the soil is
sufficiently compacted to interfere with root growth.
• The vertidrain holes were the least compacted, with
acceptable (less than 300 psi) compaction levels at
depths up to 5 inches. This is why longer roots are
able to grow in these holes, as illustrated in the
photo on page 1.
• Aeration holes were surprisingly compacted. This
may be due to the fact that the penetrometer probe
doesn’t provide accurate readings in these relatively
narrow and shallow holes.
• As you probe deeper and deeper into the soil
profile, compaction readings will get higher. This is
an expected result, because the weight of the soil
on top exerts a great deal of pressure on the soil
below, which results in compaction.
Taking your own compaction readings
Knowing just how compacted your greens are can be
useful in several contexts.
Timing of aerifications/peace of mind: If soils show an
increasing trend towards compaction, you can
schedule an aerification with the comfort of knowing
that it truly is worth the time, effort and disruption.
Measuring the impact of management programs: If
you have ever wondered how effectively soil
amendments, topdressing sands or aerification
procedures decrease compaction, you are not alone.
Taking compaction readings can help you determine
the value of these practices at your own location.
Communicating with golfers: Penetrometer readings
are hard data that can be used to educate golfers,
greens committees and managers about the value of
aerification.
Taking readings is a relatively simple procedure:
• Obtain a soil compaction tester (cone
penetrometer) from a company such as Spectrum
Technologies (800-248-8873 or
www.specmeters.com) for $199.00 If your soils
are very compacted, you may need to purchase a
gauge that reads higher than the 300 - 500 psi limit
on most penetrometers (a 2 ½” liquid filled
pressure gauge that reads up to 1,000 psi is
available for $30 from Grainger’s [model # 5A044]
[www.grainger.com or 1-800-225-5994].
• Take your readings within a few hours after
irrigation, when the soil is at, or near field capacity.
This will ensure that moisture levels are consistent
from one sampling date to the next.
• Using the ½ inch tip provided with the
penetrometer, push down on the handles, with a
slow but constant speed.
• Take note of the pressure readings at each of the
soil depths marked on the stainless steel probe
(most penetrometers have markings at 3 inch
intervals). If feasible, take along a helper and have
them record the numbers for you.
References
Adams, W.A. and R.J. Gibbs. 1994. Natural Turf for
Sport and Amenity. CAB International, Wallingford,
UK. 404 pp.
Blake, G.R. and K.H. Hartge. 1990. Bulk Density. pp.
363-375 in Methods of Soil Analysis, Part 1.
Physical and Mineralogical Methods. Agronomy
Monograph 9 2 nd edition. ASA Press, Madison, WI.
Brady, N.C. and R. R. Weil, 1999. The Nature and
Properties of Soils. Prentice-Hall, NJ. 881 pp.
Hummel, N.W. 1993. Rationale for the revisions of the
USGA green construction specifications. USGA
Green Section Record, March/April 1993.
© Copyright 2001, PACE Consulting, 1267 Diamond Street, San Diego, California, 92109 (858) 272-9897 Web Page: www.pace-ptri.com