Sports fields, golf courses, and other turf areas often deteriorate because of compacted soil, excessive thatch buildup, and excessive use. When this happens, physical disturbance (cultivation) of the sod is often required to restore its vitality. Unlike conventional crops which can be plowed, turf areas must be cultivated so that the surface is opened up without destroying its appearance (aesthetic value) and function. Cultivation of turf grasses can be accomplished by vertical mowing, core aeration, spiking and topdressing.
Vertical mowing, coring and spiking are methods of cultivating intact turf grass sod to improve the growing environment within the thatch layer or in the soil immediately below the surface. Each practice requires specialised equipment.
The vertical mower cuts by impact of whirling knives, which turn in a vertical plane on a high speed horizontal shaft. These blades are usually fixed, but may be free-swinging. They vary in thickness from 1/32- to -inch. The thinner blades are used on golf greens, where the surface must not be drastically disturbed. The interval of space between blades on the shaft can be varied. The spacing interval is determined by the desired effect and the horsepower of the engine on the unit. Power requirements for vertical mowing are 2 to 3 times that required for reel mowing.
Originally, the vertical mower was a hand-operated unit with a cutting head 18- to 22-inches in width. It was used at monthly or season intervals to cut vertically into the sod and lift out a large portion of the thatch layer. This practice was very time-consuming and was usually limited to golf greens. Vertical mowing with these units marred the appearance of the turf and required several weeks to restore color and density to the turf. A once-over with the vertical mower and the site looked as though a football scrimmage had been held on it. The practice was ultimately good for the grass, because it 1) partially eliminated the excess thatch layer, (2) cut and often reduced graininess and (3) promoted growth of many new shoots.
In heavily thatched turf, it may be necessary to set the vertical mower to cut deeply into the turf. This will groove the surface thereby necessitating topdressing with a soil mix to smooth the surface and cover exposed stolons.
With the advent of the riding triplex greens mower came multiple head vertical mowing units, which are interchangeable with the cutting reels. This equipment enables the turf manager to vertical mow fine turf very rapidly and to simultaneously collect the clippings. The latter equipment necessitated that a vacuum or sweeper be passed over the turf following vertical mowing.
With the triplex vertical mowing units, it is practical to vertical mow at weekly intervals when the turf is actively growing. The cutting blades should be set to only nick the grass surface so that the turf is not impaired. Frequent vertical mowing, together with aerification, eliminated the need to renovate turf by severe vertical mowing.
A more recent improvement in vertical mowing units is the grooming mower. The grooming mower has a vertical mowing attachment just in front of the reel cutting unit of a triplex greens mower. With the grooming mower, turf is lightly vertically mowed (or groomed) each time the turf is mowed. Thus, light and frequent vertical mowing is practical.
In summary, we can say that routine vertical mowing of fine turf will improve the playing surf ace by:
- truing the surface through removing “grain”,
- stimulating new shoot development, and
- removal of some thatch.
In addition, the vertical mower is useful at the time of overseeding bermudagrass turf with winter grasses. This vertical mowing may be more severe than routinely used during the warm months. It will (1) retard the growth of bermudagrass, thus reducing competition for the seedlings; (2) open the turf somewhat for better penetration of the overseeded grasses, and (3) reduce thatch accumulation.
Vertical mowing is not totally beneficial to turf. It may encourage more weeds and, if the height of cut is too low, it will weaken the turf and lower the quality. On bentgrass putting greens, vertical mowing should be avoided during stress periods when growth of the grass is slow.
Vertical mowing of larger turf areas is accomplished with tractor drawn mowing units which operate off the PTO. Such units usually have large blades which are set to groove the turf to the soil surface or deeper. The main purpose of this type of vertical mowing is to remove thatch and to prepare a site for overseeding. Using such a mower once or twice a year to dethatch bermudagrass lawns, fairways or athletic fields is a common practice. Where bermudagrass lawns, fairways or sports fields are overseeded each fall, the ideal time to vertical mow is several weeks prior to overseeding.
Aerification may be defined as the removal of small soil cores or plugs from turf areas, leaving a hole or cavity in the sod. Such holes aid in the movement to air, water, nutrients, and other compounds into and through the upper portion of the soil. Machines for coring turf may have hollow tines or open spoons 4 to 6 inches in length, which are – to -inch in diameter. The depth of penetration of the tines or spoons depends on the degree of soil compaction, soil moisture and the weight of the aerifier. Increasing soil moisture usually facilitates deeper penetration. Soil cores brought tot he surface may be removed or pulverized and worked back into the thatch layer. When worked into the sod, the soil intermingles with the thatch layer and aids in its biological decomposition. This is one of the most effective ways to control thatch buildup.
Aerification is most beneficial on soils with an impermeable layer near the surface and on highly compacted soils. The frequency of aerification needed depends on the degree of soil compaction. Golf greens, tees and athletic fields need more frequent aerification than less trafficked areas. In general, turf responds to aerification best in spring and later summer. Generally, 3 to 4 aerifications annually are adequate for intensively used turf areas.
Deep tine aerifiers or deep drill aerifiers are available that extract a – to 1-inch diameter core 8- to 10-inches deep. The deep tine aerifier is beneficial on sports fields and golf greens with layered profiles, impermeable layers, sand layers or other boundaries that interfere with water movement, aeration or root development. The deep aerifier is more of a renovation tool that a regularly scheduled maintenance practice.
Equipment is also available for slicing thin holes in the soil without removal of soil cores. Slicing is less effective than coring, but it can be done much faster and is often more practical for large turf areas. Most slicing machines have blades shaped like those on a sickle mower. These blades are bolted at intervals tot he perimeter of metal wheels spaced 4- to 6-inches apart on a long axle. As the wheel turn, the blade slices into the turf, cutting a narrow slit 3- to 5- inches deep and about -inch wide. Such openings do not interfere with the use of the turf.
It is often best to irrigate the turf immediately after slicing or coring to prevent excessive drying of turf at the edge of the openings made by the blades or tines.
If the soil on which the turf is growing was “ideal” in physical makeup, it is doubtful that aerification would be needed. However, such an ideal soil mixture is rarely attained, hence aerification should be a standard practice on most turf areas receiving regular traffic, whether foot or vehicular.
Spiking is a variation of “slicing”. Spiking is accomplished by forcing the small solid teeth of metal discs into the soil surface to a depth of °-to 2-inches. A typical spiking machine has about 20 disc-shaped blades which have teeth-like rowels on a spur. Wider units or tandem groups of smaller spikers are available for use on large turf areas. The spiker does not remove a soil core.
The spiker is most useful in breaking up surface crusting of soil or algae. Since a single pass of a spiker creates about 10 to 20 thousand holes per 1,000 sq. ft., it is effective in helping to “dry out” poorly drained turf areas. It also improves water penetration. Where such conditions exist on golf courses or athletic fields spiking is a beneficial practice.
Since spiking causes only minor disruptions of surface conditions, it can be practiced more than core aerification.