Topdressing & Aerification
JAMES SUA, CGCS,CCPC,CTP, CGIA
鋪砂與打洞 Topdressing & Aerification
The previous chapters covered most of the essential aspects of basic turfgrass management. However, occasionally you will encounter unusual situations that do not easily fit into one of the typical subject areas of turfgrass management. This chapter will discuss several of these common but very important problems in a question-and-answer format.
What causes thatch and how can it best be controlled?
Thatch is a partially decomposed organic layer that develops above the soil surface (Figure 1). It consists of living and dead stems, roots, crowns, and sheaths. These tissues are very resistant to decomposition. The leaf blades of the turfgrass plant do not significantly contribute to thatch build-up, since they readily decompose. Therefore, as long as the 1/3 rule for mowing frequency is followed, it is not necessary to collect clippings. In fact, as discussed, clippings left on the turf will return significant amounts of nutrients to the soil.
Thatch is caused by:枯草層(草盤層)形成的原因 :
Ø Frequent, shallow watering
Ø Excessive nitrogen fertilization
Ø Infrequent, high mowing
Ø Clay, sand, and compacted soils
Ø Thatch –producing grasses
Ø Excessive pesticide use
Ø Poor soil aeration
Ø Water deeply and infrequently
Ø Use a slow release nitrogen fertilizer
Ø Mow on a regular basis
Ø Aerate clay and compacted soils
Ø Plant low thatch-producing grass varieties
(note the larger number of roots in the thatch)
A thatch layer thicker than 0.5 inch may cause a decline in turfgrass quality. It can encourage increased disease and insect problems; reduced heat, and drought hardiness; shallow rooting; and restricted movement of fertilizers and insecticides into the soil. On the other hand, a thatch layer less than 0.5 inch thick will improve the wear tolerance of the turf and provide some insulating protection against high and low temperatures.
Thatch accumulates simply because the rate of tissue growth exceeds the rate of tissue decomposition. Any factor that stimulates rapid tissue production or impedes tissue decomposition favours thatch accumulation. For example, excessively high nitrogen fertilization, the use of vigorously growing species and cultivars, and high heights of cut will all encourage thatch development. The use of certain pesticides also increases thatch by destroying soil organisms such as earthworms that speed the process of decomposition. Thatch is primarily a problem associated with creeping/spreading turfgrasses rather than bung-type turfs.
Thatch should be controlled when it reaches a thickness of 0.5 inch or more. This can be determined accurately only by examining a vertical cross-section of the soil and turf. Simply walking over the turf and trying to “feel” the thatchiness is not a good idea. Various cultural practices (mowing height and/or irrigation) or the species itself may result in the turf feeling spongy, which can be mistaken for a build-up of thatch. A soil probe, spade, shovel, or pocketknife can be used to remove the vertical sample for inspection. Since thatch thickness can vary throughout a turfgrass site, it is important to take several samples from the turf area.
If thatch thickness is 0.5 inch or more, consider some method of removal or control. Only a few methods of thatch control are available. One popular method is mechanical removal with a dethatching machine. A dethatcher is a specialized machine with wires or blades that operate vertically to the soil surface (Figure 2). The vertical action pulls the thatch up from the soil surface to the surface of the turf, where it can be removed. The wire tines or blades are set to reach a depth just slightly below the soil surface. It is sometimes necessary to go over the turf area in two directions to achieve thorough and uniform thatch removal.
Figure圖2 : Views of a De-thatcher除枯草層(草盤層)機
The mechanical removal of thatch is a harsh practice that can cause stress to the turfgrass plant. It is recommended that there be at least 30 days of favourable growth conditions following the dethatching operation. Mechanical dethatching thins the turf and may allow weeds to encroach on the area. Also, the turfgrass area should not be dethatched after preemergence herbicides have been applied, since the chemical barrier will be destroyed.
Another method of thatch control is the use of a core aerifier or cultivation machine. Many people use the term aerification when referring to core cultivation. Coring is a process in which hollow or solid tines or spoons are used to make a vertical hole through the turf into the underlying soil. In the case of hollow tines or spoons, a turf/soil core is removed and is dropped onto the surface of the turf (Figure 3). The cores may then either be broken up and worked back into the turf by dragging steel mat or screen or brush over the area or picked up and removed. Greatest thatch reduction occurs when the cores are worked back into the thatch layer. Coring can be done whenever the growing conditions for the turf are good. Core cultivation is a slower method of thatch control, unlike a mechanical dethatcher, coring does not appear to significantly disrupt the preemergence chemical barrier.
Figure圖3 : Core cultivator. Top view of core cultivator coring pattern打洞培養機。從上方俯視打洞後的格式
Aerator holes should be 3 inches deep, 3 inches or less apart, and about three quarters of an inch in diameter. Several passes will be needed for correct spacing. This should be done twice a year on a continual basis. The benefits of aerating are soon lost if the practice is discontinued.
Turfgrass must have a constant supply of fresh air moving to the surface of every living, growing root to replace carbon dioxide. Carbon dioxide builds up continuously and needs to be released from the soil. Air exchange, or aeration, takes place in spaces between the solid particles of soil.
Aeration can be natural occurrence between the soil and its surroundings. Temperature differences between the soil and the atmosphere may result in air movement. Water activity into and out of the soil will affect the proportion do not produce a sufficient amount of aeration for a turf area to stay healthy, lush and green, additional mechanical aerating must take place.
Aerating should be as much as a part of turf area care programme as mowing, watering and fertilizing.
Compaction, excess thatch, and clay soils cause weak-rooted turfs. At these stages, it is necessary to aerate mechanically. Replanting the turf may be another answer to severe compaction problems, but the soil will have to be modified first to exact a long-term solution.
Compaction is the pressing together of soil particles, which squeezes air out of the soil. Most compaction occurs in the upper two inches of soil. The biggest cause of compacted soil is activity on soggy turf. Other causes include watering turf areas and/or excessive tilling when preparing a seedbed. Construction and grading equipment used to build homes also has adverse effects.
As soil is compacted, the soil’s aeration process becomes ineffective. Air spaces are squeezed out and filled with water. At this point, the soil is waterlogged and unable to drain. Waterlogged soil promotes shallow root growth.
Compacted soil results in turf with low energy, poor growth, and thin yellow-green characteristics. It will not hold up well to traffic or weather stress. Playing on it would tear the turf more quickly than under normal conditions. Heat stress also causes the turf to wilt sooner. Under any of these conditions, recovery takes longer than it would for a healthy turf.
The type of soil is another reason to aerate the turf area. Clay contributes to compacted soil. It has a fine texture with a sticky plate-like structure, and is most likely to become compacted. Clay soil needs to be improved before planting a turf area. To do this, add organic matter such as peat moss or compost to the soil.
There are two ways that one can find out the kind of soil on their turf areas. By having a soil test done by performing a squeeze test. Take a ball of moist soil and squeeze it in your hand. If the ball holds together, it’s clay. If it breaks apart easily then it’s loam. Sand falls apart most easily. This test works well for any flowerbed, garden, or turf soil.
Benefits of Aeration打洞通氣的優點
Aeration loosens compacted soil and breaks up thatch. It allows water and other nutrients to seep into the soil, encouraging new root growth and establishing a stronger , deeper root base for a lusher, healthier turf. Another benefit of aeration is the reduction of water runoff and puddling.
By removing cores of soil, aeration provides space for roots and soil to expand. Reducing further compactions.
Aeration is also a method of thatch control, because microorganisms brought to the surface of the turf help break down thatch. All of these factors help the turf establish a deeper root base, making the turf more heat- and drought-stress tolerant.
氧氣(O2)與二氧化碳(CO2) 在土壤中交換 通氣機
When to Core Aerate何時進行打洞工作
Core aeration can be done anytime the grass is actively growing. It is best to aerate once or twice a year on a continual basis.
It is important to allow at least 4 weeks of good growing weather. This will give plants a chance to fill open holes.
Spiking is the easiest and least expensive aeration method and is done by using a solid tine or a metal spike and putting an angular hole in the ground. Using this method, the turf heals quicker than with core aeration because no soil is being removed. Spiking can be done anytime of the year. But the effects of the solid tine method are short term. Another problem is that the soil is pushed to the sides of the hole compacting the area again.
Vertical mowing or power raking is less effective in alleviating compaction but is an excellent means of reducing thatch, particularly for warm-season grasses. The process is less destructive than core aerate and is an excellent option if compaction is minimal
Earthworms are helpful to turf areas, because they are natural aerators and thatch controllers. The tunnels they create help loosen the soil. By digesting organic matter, earthworms keep thatch production in check.
Coring is often followed by a topdressing procedure. Topdressing is the broadcast application of soil or other materials to the surface of the turfgrass area (Figure 4). Topdressing is often used to smooth the surface of a turfgrass area or to control thatch. The spreading of soil or other types of root zone materials over and into the thatch layer makes the thatch environment more conducive to microorganism activity, which is necessary for thatch decomposition. Topdressing is a slow but very effective means of controlling thatch. Topdressing material is typically applied in very thin layers to the turf; in most cases, only a couple millimetres are applied at one time. When done lightly, the topdressing procedure can be repeated several times each year. On occasion, it may be necessary to topdress more heavily. Depending on the situation (type of turfgrass species, cutting height, time of year), as much as 0.375 inches may be applied. The topdressing material should be worked down into the turf by pulling a steel drag mat or brush over the area. On smaller areas, the topdressing material can also be smoothed and worked into the turf by brushing with a push broom.
Figure圖4 : Cross-section of coring holes filled with topdressing material鋪砂材質填滿了打洞後的孔徑裡的橫切面示意圖
Topdressing is an excellent management tool. Golf greens are routinely topdressed, which accounts for the smoothness associated with high-quality greens. Golf greens that are routinely topdressed rarely develop thatch problems.