Tips for sports turf managers
Compaction can be a turf manager's nightmare. Traffic, weather conditions and normal use push soil particles closer together, reducing pore space and increasing soil density. Due to decreased air, water and nutrient movement, turf roots struggle to fill their basic needs. As a result, turf quality declines and sports fields provide less cushioning for players. Turf shows less stress tolerance and increased susceptibility to weed, disease and insect problems. Aeration and topdressing are good bets to combat compaction.
Aeration and soil compaction Aeration opens channels in the soil through which air, water and nutrients can move more freely. Aeration increases pore space, softening hard soil by allowing it to move upon impact.
Degree of soil compaction varies with soil texture, moisture content, area use and amount of weight applied. Soils high in silt and clay compact more quickly than sandy soils; wet soils compact more quickly than dry soils.
Most soil compaction occurs within the top 1 to 3 inches of the soil surface from normal use but may result from heavy equipment traffic or repeated aeration to the same depth.
Years ago a high school football coach told me that hard soil just helped toughen the players. I said, "Great. Why don't you just practice in the parking lot?" He then spat out some tobacco juice and stared at me as if he were comparing the options.
Consider your aeration alternatives based on the hardness of the soil, weather conditions, turf-growth cycles and field-use schedules. Check for soil compaction by using a soil probe, shovel, blunt rod or screwdriver.
Deep or shallow Shallow aeration reaches into the top 3 or 4 inches of soil. Equipment using solid spikes pokes holes in the soil, creating openings without removing soil. Equipment with hollow tines or spoons removes soil cores and deposits them on the soil surface. In most cases, hollow tines or spoons are better. However, solid tine equipment that causes soil lifting and vibrating can be quite effective. Using any equipment regularly at the same depth can cause development of a compacted layer. Deep aeration extends below the 4-inch level and helps improve both surface and deep-soil problems.
Ideally, aeration should reach the depth of compaction yet cause minimal surface disruption. Equipment that brings soil to the surface is the most disruptive, but because it makes a greater change in existing conditions, it can produce the most long-lasting results. Even when you drag cores back in, the turf needs time to recover and grass roots need to regenerate and spread deeper into the soil. Because spiking and slicing is less disruptive to turf growth and appearance, you can use it more often than coring.
Consider using different types of cultivation at different times. Perform the more disruptive aeration before major root-growth periods - such as spring and fall for cool-season turfgrasses and spring for warm-season turfgrasses. Shallow aeration before deep aeration should make both more effective.
Proper soil moisture enhances aeration effects. Dry soils are hard to penetrate, limiting the effect of the procedure and stressing equipment. Wet soils may not move enough to achieve satisfactory results. Generally, soil moisture should be at field capacity when you aerate. For vibrating and shattering aerators, the soil should be slightly drier. Field capacity generally exists 24 hours after a rain or irrigation. Hot, dry weather and strong winds may dry out the turf bordering aeration holes. Therefore, avoid aeration during such conditions or compensate for moisture loss with irrigation.
Topdressing Generally, the longer aeration holes remain open to the surface, the longer lasting the effect. A sealed hole, even if only at the surface, significantly reduces air- and water-movement benefits. Topdressing with a porous material, sand or a coarse-textured soil, keeps the holes open.
Repeated topdressing over a long period, especially in conjunction with aeration, provides other benefits. Topdressing can improve the soil profile, provide protection for turf seed and young plants, protect the crowns of existing turf, improve drainage, help decompose thatch and aid in leveling uneven surfaces.
Topdressing programs vary according to the changes you desire, soil profile, type and condition of the turf; degree of compaction; turf growth cycles; weather conditions and use.
Generally, it's best to match the texture of the topdressing material with that of the existing soil to avoid layering. Topdressing with sand is common on golf-course greens because greens are about 90 percent sand. However, unless you are committed to two or more topdressings for 3 or more years, or have a field of sandy soil, sand may not be the best bet for general-sports fields. Mixing a small amount of sand with soil may worsen soil conditions, not improve them. In most cases, the simplest approach is to allow aeration soil cores to dry, then drag them back over the turf as the topdressing material.
When you need additional topdressing material, the rate or thickness of application will vary, depending on time and budget, playing season and growing season or weather conditions, and whether core aeration has preceded topdressing.
Calibrate your spreader Inconsistencies in materials or application thickness may create layering of different textures and may hamper, rather than improve, air, water and nutrient movement.
To avoid these problems, calculate the rate of application precisely and calibrate equipment carefully for uniformity. A 0.125-inch layer of topdressing is 10.5 cubic feet or 0.4 cubic yard per 1,000 square feet. Topdressing a baseball infield of 17,000 square feet takes one-third the time and material that topdressing a 57,600-square-feet football field does.
Most cultural practices, including topdressing, reduce turf quality and growth temporarily. The combination of aeration and topdressing will cause greater stress than either alone. However, fertilizing a week or two before cultivation can increase recovery rate.
Aeration and topdressing make a major impact in your overall turfgrass management program because the turf root mass is concentrated in the upper 6 to 8 inches of the soil profile, where these practices most improve soil conditions.
Dr. Gil Landry is an extension turfgrass specialist with the University of Georgia (Griffin, Ga.). He is a past president of the National Sports Turf Managers Association.
Keep detailed records of aeration and topdressing procedures each year. Include not only what and when equipment was used and what materials were applied, but growing conditions, temperature and rainfall as well.
Also record turf use, including the number and conditions of games and practices on each field. Wet fields result in more damage than dry ones. Although good soil moisture is great for turf growth, playing on fields with damp soils can increase soil compaction.
Assess the effectiveness of your aeration and topdressing programs. Check core samples for root growth, moisture retention and compatibility and be flexible enough to make adjustments as necessary. Also, record resulting benefits to turf health, including reductions in irrigation, fertilization, weed, insect and disease problems. You can use the documented data for budgeting and to support funding requests for equipment and procedures.
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