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Turf and soil response to core aeration Sampling technique Year % surface area affected/ year† Turf quality (1-9)‡ Bulk density (grams/cubic centimeter) Surface hardness (gMax)§ 46.6a Thatch organic matter content// Thatch depth Infiltration ounces/ square inch grams/ square centimeter inch millimeters inches/ hour centimeters/ hour 0.237 1.02a 0.57a 14.4a 59.1a 150a 2008 15 7.1a†† 1.25a 25 6.8b 1.19b 46.8a 0.213 0.94a 0.54a 13.8a 63.8a 162a 2009 15 7.1a 1.42a 53.6a 0.266 1.17a 0.50a 12.8a 62.2a 158a 25 6.7b 1.36b 51.7b 0.254 1.12a 0.50a 12.6a 63.8a 162a † % surface area impacted per year. Averaged across all rating dates. § Relative surface hardness value quantifies deceleration of 4.96-pound (2.25-kilogram) weight dropped from height of 17.7 inches (45 centimeters). // Ashed organic weight of thatch layer per square centimeter of surface area. †† Values followed by different letters within the same year are significantly different. ‡ Table 2. Response of turfgrass and soil physical properties to core aeration affecting 25% and 15% surface area per year averaged across all rating dates and number of core aeration events per year in Clemson, S.C., June−August 2008 and 2009. Turf quality Any conversation about core aeration includes a discussion of its effect on turf quality. Understanding how turf quality is affected by the percent surface area removed and the number of core aerations per year is necessary to properly evaluate the trade-off between reduction in turf quality and improvement of soil physical properties. When considering only the amount of surface area removed per year, turf quality was improved 4% in 2008 and 6% in 2009 by reducing the amount of surface area removed (Table 2). With less surface disruption, the turf required less time to fully heal from core-aeration injury, which contributed to the overall improvement in turf quality. After initial core aeration on June 1, turf quality was unacceptable (<7) for approximately four weeks in 2008 and six weeks in 2009, regardless of amount of surface area removed. After these periods, in treatments involving two and three core aerations, turf quality generally improved but was reduced by subsequent core aerations on July 4 and Aug. 15 (Table 3). In 2008, removing 15% or 25% of the surface area in a single core aeration initially reduced turf quality more than treatments removing these amounts through two or three core aeration events. Although the initial injury after removing 15% or 25% surface area in a single core aeration may be unacceptable to some turf managers, turf quality in these treatments was considered acceptable for more cumulative weeks throughout the study when compared to treatments with two or three core aerations. In 2009, initial turf-quality reductions were not as severe because less surface heaving occurred during core aeration. Bulk density or soil compaction Soil bulk density is the mass of dry soil per given unit of soil volume. If interpreted correctly, bulk density can provide insight into the degree of soil compaction. An excessive increase in bulk density will result in reduced macroporosity, nutrient and water availability, oxygen concentration, and speed of surface water infltration. Failure to adequately perform core aeration will cause soil to become excessively dense over time. The optimal value for bulk density varies depending on soil texture. For sand-based putting greens, bulk density should fall between 1.25 to 1.55 grams/cubic centimeter to provide a balance of soil aeration, water retention, nutrient availability, and oxygen concen- tration (5). Bulk density should be a major consideration during the planning stage of a cultivation program and should be measured every two years. In this study, bulk density decreased 5% in 2008 and 4% in 2009 by increasing surface area removed per year from 15% to 25% (Table 2). Increasing the number of core aerations per year from one to three reduced bulk density 8% in 2008 (Table 4). In 2009, increasing the number of core aerations from one to two reduced bulk density 4%. Bulk density was similar between treatments with one and two core aerations in 2008 and two and three core aerations in 2009. Although the effect of the number of core aerations per year on bulk density was somewhat inconsistent between years, bulk density generally decreased as the percent of surface area removed and the number of core aerations per year increased. Surface ardness Surface hardness, or frmness, is a measure of soil compaction and surface cushioning due to thatch accumulation and soil strength. Since measurements made with the Clegg impact hammer are a relative barometer of surface frmness, the effects discussed here should be used during the planning stages of 01.14 GOLF COURSE MANAGEMENT 143

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