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Study Shows Benefits of Deep-tine Aerification on Heavily Compacted Athletic Fields

Chris Derrick, Beth Guertal, and Joey Shaw

Athletic field managers recognize the results of turfgrass wear and compaction. Worn spots, torn turf, and bare patches are visible signs of the effects of foot and vehicle traffic on soccer, football, and other athletic fields. Foot and vehicle traffic also causes soil compaction, which decreases depth of rooting, hinders water and nutrient uptake by the grass, and increases turf stress. As every turf manager knows, topdressing and aerification are two solutions to alleviating soil compaction and turf wear.

Although aerification is widely used to relieve soil compaction on athletic fields, relatively little scientific research has been conducted in that area. In fact, little is known about what types of aerification equipment work best, what type of tines are most effective (hollow? solid?), or what sort of frequency is needed (once a year? every month?).

In an effort to answer some of these questions, AAES researchers recently completed the first year of a two-year study in which they examined the effectiveness of a deep-tine (12 inches deep, 3/4 inch in diameter) Model SR-48 Southern Green Soil Reliever and its impact on reducing soil compaction based on aerification frequency.

One of the athletic fields selected for the study was the Auburn University Marching Band Practice Field, a hybrid bermudagrass (Tifway) field that receives a great deal of traffic throughout the year.

For the study, treatments consisted of either one aerification per year (July), two aerifications per year (July and April), or four aerifications per year (July, April, October, and January). A January aerification typically is not recommended; it was simply done during that season so that the treatments in the research project would be evenly spaced over time. These aerification treatments either received or did not receive a sand topdressing, making a total of six treatments in the study.

To evaluate how well the aerification worked, researchers used a soil penetrometer. This device is a three-foot-long steel rod with a two-inch diameter load-sensing head. The soil penetrometer, slowly pushed into the soil to a depth of six inches, measures how difficult it is to push the tip through the soil. This number was recorded as “soil resistance.” Other data collected during the study included bulk density, surface soil hardness, root volume, spring greenup, and water infiltration rate.

The results? On the heavily compacted AU Band Practice Field, deep-tine aerification decreased soil compaction. Figure 1 illustrates how compaction was relieved over a six-inch soil depth when just one aerification was applied in November, as compared to plots that had not been aerified. Deep-tine aerification effects were best seen in the one- to six-inch depth. The presence of a thatch layer in the bermudagrass is the most likely reason the effects of aerification were not seen in the surface to one-inch depth.

Figure 1. Soil compaction as affected by one deep-tine aerification, 0-6 inch sampling depth, November, 1998.	Figure 2. Soil compaction in 1998 at the AU Band Practice field as affected by the number of deep-tine aerifications, 0-6 inch sampling depth.

When viewed over the entire year, the impact of continued aerification can be seen (Figure 2). Four aerifications (January, April, July, and October) resulted in a greater overall decrease in soil resistance than one or two aerifications. The July data point shows the overall treatment effects, as the plots had received their yearly totals of one, two, or four aerifications. Each additional aerification during the year helped decrease soil compaction.

The effect of the aerification did not last long, however, as the three lines for August, September, and October lie directly on top of each other. Thus, in the time of heaviest traffic (AU Band practice starts in July, illustrated by the rapid increase in soil compaction in Figure 2), monthly aerifications are needed to alleviate soil compaction. Once the October aerification had been applied (part of the four-aerification treatment), the November and December data points show significant reduction in soil compaction.

Other benefits of aerification also were observed this past spring, as the more frequently aerified plots greened earlier in the year and had less annual bluegrass, an undesirable weed, on them. The plots were also softer, as recorded via surface hardness, and they had a lower bulk density than the plots that received only one aerification.

In conclusion, this one year of data revealed that deep-tine aerification of compacted athletic fields did reduce soil resistance. Effects of the aerification typically lasted about two months, unless the field received heavy traffic. When the field was exposed to heavy traffic, effects of the deep-tine aerification lasted less than one month.