Use Science to See if Your Greens Aerification Program is Working or Not

Eric von Hofen and Soil Profile on Tifeagle green
Dr. George Snyder of the University of Florida has a great system to track and determine if your aerification program is working or not. I have been working with him for a number of years tracking thatch, percolation rates and organic material levels in Tifeagle Bermudagrass greens. We have been pulling soil samples from the same greens and locations for over 6 years. Maintaining Tifeagle greens in South Florida is very difficult because the growing season never stops and it rains 70 inches a year. Greens have to drain and the roots have to get oxygen. My golf course has very poor water quality and every night I water the greens, I know that I’m closing down the percolation rate and growing organic material. This is the main reason why I aerify my greens 4 times a year and verticut them 25 times. I use Dr. Snyder’s tests to see where I stand two times a year. We pull samples in the Spring to see how bad things have gotten during the Winter and then we pull them again in the Fall to see how much we corrected with an aggressive aerification program. The following information explains this testing process in more detail. Please forgive me for taking out some of the tables and charts in efforts to shorten this post.
Eric von Hofen and


On September 28, 2010, greens 11 and 15 were sampled as they have been in the, past. Four 2-inch diameter “undisturbed” cores 0-3” deep were taken from the back to front of each green. In addition, these same greens were sampled to a depth of approximately 8 inches using a 3/4th inch diameter coring device. Eight cores were collected and composited on each green. The verdure/thatch layer, which will be termed “thatch”, was separated from the lower organic matter (OM) stained layer subjectively by cutting with a knife at the depth where resistance to cutting decreased substantially. The thickness of the layers was recorded, and both the thatch layer and the underlying organic matter-stained layer were retained. Organic matter was determined on these layers as weight loss following ignition in a muffle furnace at 550C. Mineral particle sizes were determined on these samples by passing the ignited residue through a nest of sieves using a RoTap shaker. For this analysis, material from greens 11 and 15 was combined to provide a sufficient quantity of sample for the analysis.

Saturated hydraulic conductivity (Ksat) was measured on the 0-3” cores which contained the grass and thatch, generally following the procedures specified by the United States Golf Association (USGA Green Section Record, March/April 1993). However, it should be noted that the USGA procedures were designed to predict the suitability of root zone mixtures for greens construction, and not for analyzing undisturbed cores from existing greens. For example, the procedure calls for compacting the mixture prior to analysis. For the undisturbed cores, laboratory compaction does not seem appropriate and was not conducted. The USGA procedures do not assume that turf is present, as it was in the 0-3” cores. Seven, 1/4th inch holes were drilled 1-1/8 inch deep in each core and Ksat was again determined to gauge the effect of the thatch layer on Ksat.

Results and Discussion

On the average, the thatch layer averaged 0.9 inches (0.89 inch on green 11, 0.95 on green 15), which is the thickest it has been since September of 2008 (Table 1). The underlying OM-stained layer averaged about 3 inches (3.1 inches on green 11, 3.0 inches on green 15), which continues the steady increase in stain depth that has been occurring for years (Table 1). I feel this might be growing due to a heavy topdressing program that adds a quarter inch to a half inch of new sand every year to the greens.

Although the stain layer is increasing in thickness, the organic matter (OM) content of the OM-stained layer below the verdure and thatch averaged 1.8% by weight (1.8% in green 11, 1.9% in green 15, Fig. 1), which is the lowest it has been in over 4 years (Table 2). Concern has been expressed about OM accumulation in greens in amounts greater than 3% (USGA Green Section Record, Jan-Feb 2004, pgs. 11-15), although this information was primarily developed for bentgrass greens. Regardless, the stain-layer OM content is well below this value.

Organic matter in the thatch/verdure layer (termed “thatch”) averaged 7.5% (Table 2), being 7.5% in both greens. In the past, the OM content of the thatch has been lower in the fall than in the previous spring. This fall, however, it is unchanged from the previous spring sampling, and is greater than in the previous fall samplings (Table 2). While I am not aware of published recommendations for thatch OM, I believe low OM is conducive to water and air permeability in the thatch.

Saturated hydraulic conductivity (Ksat) averages somewhat greater than it was a year ago, although it is lower in green 11 than in this past April (Table 3). The USGA has recommended Ksat values of 6 to 12 inches per hour for root zone mixes used for greens construction (USGA Green Section Record, March/April 1993), and it is well known that Ksat generally decreases as a green matures (USGA Green Section Record, March/April 2010). However, the values observed on these two greens still are well within the USGA specifications for new greens and are greater than those often observed in mature greens. The variation in Ksat among cores within a green, as illustrated by the coefficient of variation calculation (CV), has been greater in the spring than in the fall (Table 4). This trend continued for green 15. The CV for green 11 was unusually low in the spring, so the CV is higher this fall, but it is only a little higher than in previous fall measurements (Table 4). On both greens, Ksat was lower for sample D, which is the front of the green, but this may just be a coincidence.

Based on the observation that drilling holes through the thatch increased Ksat more in cores that had lower Ksat before drilling than in cores with higher Ksat, and that this relationship was fairly strong (Fig. 2), thatch is having some effect on Ksat. However, the overall Ksat values on the original samples are quite good, and average well within the 6-12 inch range that the USGA has given as a criteria for a root zone mix used in new greens construction. Favorable Ksat is being maintained in these greens regardless of the influence of the thatch.

Based on previous measurements, the mineral particle size ranges are within USGA recommendations for putting green construction in the > 3-inch region of the greens, which is assumed to be the material from which the greens were constructed (Table 5). However, in the thatch there is less coarse+medium sand and more fine sand than is recommend (Table 5). There is a trend for very coarse and coarse sand to increase with depth, and for fine and very fine sand to decrease with depth (Table 5). This is the opposite of what generally is considered to be conducive to air and water penetration and movement in the root zone. If the profile is not entirely consistent throughout, water and air movement is improved by having increasing coarseness in texture towards the surface.

There has been a trend for coarse sand in the thatch to decrease over time, and for fine and very fine sand to increase over time (Table 6). However, these trends appear to have been arrested, or reversed, in the most recent sampling (Table 6).


Even though the depth of the stained layer below the thatch has been increasing, the content of OM in this layer is under 2% (by weight), and has been decreasing for four years.

Thatch thickness is greater than in recent samplings, and the OM content of the thatch is greater than in past fall samplings.

Saturated hydraulic conductivity (Ksat), a measure of root zone porosity, is in a favorable range

The texture of the root zone is less coarse in an upward direction, but the trend in the thatch has slowed or reversed.

Dr. George H. Snyder and Eric J. von Hofen

Fig. 1. Stain-layer organic matter and saturated hydraulic conductivity (Ksat) over six years of testing.
  eric von Hofen

For more information or testing with Dr. Snyder please contact him at

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