PHOTO: STEVE TRUSTY, TRUSTY & ASSOCIATES
It Starts with the Soil
- Soil is the growing medium for turfgrass. Understanding the texture and structure of your soils provides the basis for understanding how your grass plants will perform within that environment and under your field use schedules. This will ultimately lead to the development of your aeration program.
- Commercial soil probes are available to check the soil profile of your fields. These probes may be flat or circular, in different widths, diameters and depths. They slice into the soil to pull out a section for examination.
- You’ll want to remove a section 6 to 12 inches deep. This shows the top of the turfgrass. Then you’ll find the thatch, a dense, fibrous layer of living and dead grass stems, leaves and roots that accumulates between the actively-growing turfgrass and soil surface. A thin layer of thatch, 0.5 inches or less, is good. It helps moderate temperature extremes, limits weed growth and provides cushioning for play.
- The soil profile is below the thatch. The sample will reveal the depth and degree of turfgrass root growth within the soil. The soil sample also will show if there are different layers of soil types within the soil profile. Different layers will cause problems with water and air movement within the soil profile and will impact root development.
- Going back to basics will help you identify those layers. Soil is made up of rocks and minerals, organic matter and water. The mineral particles are broken into three categories defined by size, with sand the largest, silt the middle-sized and clay the smallest. Soil texture describes the proportion of these soil particles in soil types, which refer to the fineness, or coarseness, of a soil. The soil texture determines characteristics that impact plant growth: water-holding capacity (the amount of water the soil will retain); permeability (how easily and quickly water and air are absorbed into the soil and move through it); and workability (how easily the soil can be tilled or penetrated).
Thatch is a dense, fibrous layer of living and dead grass stems, leaves and roots that accumulates between the activelygrowing turfgrass and soil surface. A thin layer of thatch, 0.5 inches or less, is good. It helps moderate temperature extremes, limits weed growth and provides cushioning.
Benefits of Aeration
- Reduces soil compaction.
- Improves the air exchange between the soil and atmosphere.
- Enhances soil water uptake.
- Improves fertilizer uptake and use.
- Improves soil microbial activity.
- Contributes to stronger turfgrass roots.
- Helps to breakdown thatch.
This is a type of soil probe used to pull a sample of the soil profile. Note the small area to the side of the probe from which the section of soil has been removed (magnified above).
- Compaction is compression of the soil, which reduces the movement of air, water and nutrients through the soil profile. Compaction issues — caused by heavy traffic — drive the need for frequent aeration on sports fields.
- Sandy soils are most permeable, but have less water-holding capacity. Clay soils are the least permeable, but retain more water. The higher the clay content, with small particles fitting closely together, the more easily the soil will be compacted.
This soil sample, pulled from a sand-based sports field, shows two distinct layers within the soil profile.
- Multiple methods of aeration are available to the sports field manager. Match the method to field conditions within the parameters of need and field use schedules. Aeration may cover an entire field or only problem areas, such as soccer goalmouths and sidelines, or between the hash marks on a football field. It may be performed on the top 2 to 4 inches of the soil profile, or focused on a deep subsurface layer of compaction.
- Traditional aeration methods are coring, spiking and slicing. Core aeration is the most aggressive method. Hollow tines in varying diameters are used to remove soil cores from the turf. This method opens up the most subsurface area. It also causes the greatest degree of surface disruption, as the cores of soil topped with tufts of grass are deposited on the turf surface. The cores may be removed and composted off the field. Or they may be broken up mechanically, with the soil dragged over the surface as topdressing and the tufts of remaining grass are blown of the surface and removed.
- Spike aeration uses solid tines of various widths to puncture the turf and the soil below it. This opens the holes the width of the tine and the depth of the soil penetration of the tine.
- Slice aeration uses circular discs of varying sizes and shapes to cut through the turf into the soil at varying depths. This creates slices within the soil the width of the disc and the depth of the soil penetration of the disc. Both methods cause minimal surface disruption.
- Additional methods have been introduced along with the specialized equipment to deliver them. One method is the addition of quake or shatter movement within the soil profile during the spiking or slicing process. This increases the effectiveness of the spiking or slicing, extending the breakup of compaction within the surrounding area. Typically, these methods are accomplished with little or no surface disruption.
- Pressurized water injection is another method of aeration. This often is combined with, or a byproduct of, control product applications. It leaves little or no surface disruption.
- Pressurized air injection is a relative newcomer to the aeration market. This method uses probes to inject pressurized air at differing depths within the soil, fracturing the compaction. This method causes no surface disruption.
This soil sample, pulled from a different sports field, shows multiple layers within the soil profile.
- While spot aeration may be needed any time that safety and playability make it necessary, aeration is best timed to turfgrass active growth periods.
- For cool-season turfgrasses such as Kentucky bluegrass and perennial ryegrass, spring and fall is best. For warm-season turfgrasses such as bermudagrass and zoysiagrass, mid-spring after green-up and summer are best.
- Core — and some forms of spike — aeration may be timed to coincide with other maintenance practices, including fertilization, topdressing and overseeding, to create openings in the soil to enhance those procedures.
- Always be aware of the feel of the playing surface to the athletes, striving for consistency. Don’t overaerate, which could produce spots of too-soft footing.
Slice aeration uses discs of varying sizes and shapes to cut through the turf into the soil.
Plot and Record
- With multiple fields, different types of field construction, different types of sports play and differing maintenance practices and use schedules, you may have a wide variety of soil profiles across your fields and even within a single field.
- Identify these soil types and record them on an accurate map of the fields you manage. Record all aeration practices on the map as well, including date, weather conditions, method and equipment used, depth of aeration and how many passes are made in which directions. Track turfgrass reaction, including changes in rooting depth.
Hollow tines, or spoons, are used for core aeration.