Landscape and Irrigation is read by decision makers throughout the landscape and irrigation markets — including contractors, landscape architects, professional grounds managers, and irrigation and water mgmt companies and reaches the entire spetrum.
Issue link: http://read.dmtmag.com/i/103454
The effect of the different sizes of aerification equipment on the relief of compaction as measured by soil resistance was studied.The deep-tine aerifier reduced soil resistance from 3.5 inches down to 7.6 inches, but did not reduce compaction in the top 3-1/2 inches.The standard-tine unit did reduce resistance significantly in the top 3 inches, but had no effect deeper in the soil. The long-term effects of continued aerification with a standard-tine unit fitted with solid tines (5/8-inch diameter) for 3 years in a row, at a depth of 2.3 to 5 inches, showed that there was significantly more resistance than in unaerified plots. This indicates that a layer of compacter soil (known as a "pan" or "aerification pan") had developed near the bottom of the tine stroke. This illustrates the need for periodic deep tine aerification to avoid this problem. The pan of compacted soil was less severe when hollow tines were used, but still could build up over time. When the surface hardness of the turf was measured using a Clegg hammer, all forms of aerification produced a softer surface at least for one week after treatment. The standard tine aerifier with hollow tines tended to produce the softest surface. Conclusions * Compaction of turfgrass soils lowers the percent macropores in the soil; a de- Photo provided by Toro crease in macropores limits soil aeration, which hurts root growth. * Core aerification, especially solid tine, may not help eliminate thatch. * Effects of aerification in heavily trafficked soils may be short-lived (about 1 month). * Diagnostic techniques for detecting compacted soils, such as infiltration measurements or soil penetrometer readings, are widely variable, even across supposedly uniform surfaces such as a putting green. * Compacted "pans" develop over time at the bottom of the tine's penetration into the soil, especially when using solid tine equipment. * Deep tine equipment is more effective at reducing soil compaction at depths below 2.5 inches. LI Beth Guertal is a professor of Agronomy & Soils at Auburn University; Dave Han is an associate professor of Agronomy & Soils at Auburn University. Things Measured in Turfgrass Compaction Experiments Soil bulk density Bulk density is defined as the mass of a unit volume of dry soil. To collect a bulk density reading, a sample of known depth and diameter (typically 6 inches deep and 3 inches in diameter) is removed from the soil. The soil sample is dried and weighed and the bulk density is expressed as the mass per volume (grams per cubic centimeter). As the soil is compacted, the bulk density increases, because more soil particles are forced into a smaller volume and soil pore space is reduced. Sandy soils typically have a higher bulk density than soils high in clay or loam, because sandy soils have few of the very small pores associated with finetextured soils that have clay and organic matter. Additionally, sandy soils that contain sand in a range of sizes (as is a typically sand-based putting green) are already www.landscapeirrigation.com Soil penetrometer readings A soil penetrometer is a device used to measure the compaction of the soil. What is actually measured is the resistance, or amount of pressure needed to push a tipped rod through the soil. The rod tip is equipped with a load-sensing cell, and the soil strength is recorded as the tip is pushed down through the soil. ring infiltrometer, which consists of two metal rings (one approximately 12 inches in diameter and the other approximately 18 inches), with the smaller placed inside the larger. Water is added to both rings until a height of water is maintained for a period of time, which indicates that the underlying soil has become saturated. The drop in the height of water inside the smaller ring during a given period of time is used to calculate the saturated hydraulic conductivity, which is reported in units such as inches per hour. Hydraulic conductivity Hydraulic conductivity is the ease with which soil transmits water. In turfgrass what we often measure is the saturated hydraulic conductivity, which occurs when all soil pores are filled with water. Saturated hydraulic conductivity is typically measured using a double Clegg impact readings Typically used to measure the hardness of a turf surface, the Clegg hammer calculates the hardness of a surface based on its reaction to a weight dropped on the surface from a consistent height. — Dr. Beth Guertal and Dr. Dave Han tightly packed, as smaller sand grains fit in between larger. Landscape and Irrigation 17