Turfgrass Council of North Carolina – Turfgrass Cultivation Tools: Where, When and How to Use Them in Your Cultural Program

March 16, 2020 | Turfgrass Council of North Carolina | PODCAST

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North Carolina Turfgrass – Barry Stewart, Ph.D., Associate Professor, Sports Turf Science, Mississippi State University

Unlike most other crops, turfgrass soils are rarely exposed to tillage and therefore many turfgrass soils become compacted due to traffic. Our cultivation program is our best defense against soil compaction and the myriad of problems it can cause. In turfgrass, nearly everything we do — mowing, fertilizing, topdressing, rolling, playing games, etc. — happens on the horizontal plane. Turfgrass cultivation is one of the few things that happens on the vertical plane (I borrowed this from Dr. Trey Rogers at Michigan State). As we maintain and use turf soils, downward forces are applied and soil particles are pushed closer together. Soil pores, particularly macropores, are eliminated and the bulk density of the soil increases. If we think of an “ideal soil” we think of one that has 50% pore space and 50% solid space. When we consider that quartz is the dominant mineral in soils, then our ideal soil would have a bulk density of 1.33 g/cm³ given that the density of quartz is 2.65 g/cm³ (83 lbs/ft³). A bulk density range of 1.2 to 1.5 g/cm³ is a good working range for healthy turfgrass. Once bulk densities creep above 1.6 g/cm³ root growth begins to be affected and at bulk densities above 1.9 g/cm³ root growth nearly stops. Roots are not drills, they grow in the pore space, and compacted soils have less and less pore space, particularly macropore space and therefore limited root growth.

The second benefit of cultivation is the control of thatch and organic matter accumulation. In cultivation we break up the organic material accumulating at the turf surface. Sometimes the material is removed when we harvest the cores after aerifying or sweep up the clippings after we vertical mow or fraze mow. By keeping the rootzone in a favorable state of aeration, organic matter accumulation will be kept to a minimum as oxidation will proceed at its maximum rate. As organic matter accumulates and compaction happens, the rootzone is less well-aerated and organic matter decomposition slows down and organic matter accumulation increases. This leads to more moisture being held in the soil making it more vulnerable to compaction, and we begin on a downward spiral in which turf cover is lost. Topdressing is another tool in this battle with organic matter accumulation and will be the subject of a future article.

This article is written with warm season grasses in mind. The need for cultivation will vary with grass type and soil type. In general, native soils have a greater need for cultivation than sand-based soils. It is ironic that sand-based turf is more likely to receive cultivation than a native soil, but this is probably not surprising given the cost to establish and maintain grass on sand construction. Bermudagrass and zoysiagrass make up the vast majority of sport turf surfaces and require more cultivation. Some St. Augustine and centipede grass that receives traffic may also need occasional cultivation, but this should be done carefully. To ensure rapid recovery from any cultural practice mowing, make sure we have temperatures favorable for turf growth, 70 degree nights or 150 days with plenty of water available.

Core Cultivation / Hollow Tine Cultivation

Hollow tine cultivation is the cornerstone of any cultivation program. It should be a “showstopper” in that it should be a scheduled event. My mind’s picture of the benefit of core cultivation is that as our turfgrass soil becomes compacted, the elevation of our surface would decline. When we pull cores, we create a new large pore (the hole) and bring material back to the surface. As the cores are broken up and drug back into the holes not all of the material will fit into the holes and some will remain on the surface adding elevation to the surface. If the cores are collected and new material is top-dressed onto the site, it is likely that enough material will be added to provide an increase in surface elevation.

Core cultivation equipment has come a long way since John Mascaro introduced the first vertical overhead aerifier in the 1940’s. Prior to this the tool of choice was a rolling aerifier (Figure 1). Modern aerification equipment works smoothly and feature a wide range of tine diameters to choose from. Core diameter can range from 5 mm to 25 mm. Working depths can range from 25 mm to 250 mm (Figure 2). Depths longer than about 4 inches (100 mm) are considered to be “deep tine” aerification.

After the introduction of aerifiers it was found that compacted cultivation pans began to form after several years of aerification at the same depth. Incorporating deep tine aerification into a program occasionally breaks up this pan and keeps it from becoming problematic. Hole spacing can range from 1 inch x 1 inch (25 mm x 25 mm) to 6 inch by 6 inch (150 mm x 150 mm) and is determine by spacing on the machine and ground speed. In general as tine size decreases so does tine spacing. It would be reasonable to pull 3/8 inch (9 mm) cores on 1 inch centers but unreasonable to pull then on 6 inch centers, likewise pulling 3/4 inch cores on 1 inch by 1 inch centers is unreasonable.

Solid Tine Cultivation

Solid tine cultivation produces a hole but does not remove a core. As the walls of the hole created slough off and fill the hole with time, compaction is relieved and a zone of better aeration is created. Solid tine cultivation can be a very valuable tool in loosening up severely compacted areas to allow hollow tine coring. Solid tine cultivation improves soil aeration but does not remove any material from the profile therefore it has a minimal effect on thatch and organic matter accumulation. It does break up layering and improves infiltration and drainage. The larger the tine the longer lasting the effect will be.

Solid tining has the advantage of no cores to process and no clean up. The fields or greens are immediately playable. It is debatable whether or not topdressing should follow solid tining. Topdressing will smooth out the surface and fill the holes which could aid playability, however we are also adding material to our soil profile which means we increased our soils density. Perhaps as a once in a while practice this may be allowable but this should not be an every time practice. Also some hollow tining must be incorporated into this process to remove some material.

We did an experiment to examine aerification frequency on the MSU Golf Course in 2002 (Table 1). We used six treatments and replicated each on three greens. We used 6 inch (L) x 1/2 inch tines. We found solid tining twice monthly in two directions reduced greens hardness the most. There was not a great amount of separation among these treatments.

Vertical Mowing

Vertical mowing is a cultivation tool that is more focused on thatch and organic matter accumulation than on improving the physical condition of the soil, although it does have an effect on breaking up layering near the surface. Vertical mowing equipment ranges from greens equipment with thin blades and narrow spacing to larger area models with thicker blades and wider spacings. Think of circular saw blades. These blades spin into the canopy and remove material as well as severing stolons and rhizomes (Figure 3). Working depths can range from a surface tickle to about 1 inch in depth. Deep depths generate more material that must be removed to make our surface playable again. Vertical mowing is often followed by topdressing to smooth out the surface. During the growing season some golf greens are lightly vertically mown and top-dressed weekly to control grain and organic matter accumulation. Fairways and athletic fields would benefit from vertical mowing once or twice during the growing season. To ensure rapid recovery from vertical mowing, make sure we have temperatures favorable for turf growth, 70 degree nights or 150 days with plenty of water available.

Fraze Mowing

Fraze mowing is much like vertical mowing except that fraze mowing completely removes all surface materials to a set depth. Fraze mowing can be used to just remove the verdure and the thatch/mat layer or as deep as 2 inches below the soil surface. The material removed flows onto a conveyor belt and is deposited in a debris wagon for disposal (Figure 4). In many cases the material removed is a fantastic source of springs that could be used to plant or renovate a nearby field. Fraze mowing generates large amounts of clippings/spoils that must be disposed and planning for that should be part of the process. Fraze mowing will remove surface layering, thatch and accumulated soil organic matter. The regrowth from fraze mowing can take as little as 21 days to as long as six weeks. In Matt Carpenter’s research (Carpenter, 2019) on fraze mowing at MSU we found that fraze mowing was very effective in removing overseeding in the month of May. Fraze mowing was also found to be an effective way to establish overseeding in the fall, with a mid-October date being most effective. Keep in mind that a field will not be playable for at least 3 weeks following fraze mowing. Fraze mowing may not be an every-year tool but certainly one to consider occasionally as a field renovation. Fraze mowing produces a clean new surface that is free of senescent leaves for a few weeks and during that time the field looks outstanding. Fraze mowing has proven to be very effective in removing a dead surface in the renovation process. Some fraze mowing equipment such as The Turf Plane have the ability to level while they fraze mow. These machines have great utility in removing lips on baseball and softball fields as well as helping to maintain field smoothness (Figure 5).

Rotary De-compaction

I think of these machines as being the parabolic plows and deep ripping subsoilers that are used to remove compaction pans from agricultural fields. These machines are beginning to be used more to remove compaction from fairways and athletic fields. A blade that is 10 to 12 inches long is rotated into the soil and the arrangement of the blades along the shaft produces a quaking action as the machine moves forward (Figure 6). The result is a continuous slit in the soil on 8 to 12 inch spacings. They do very little to remove thatch but do loosen up a surface. Research is needed to document the compaction relief achieved and the longevity of this relief. Some companies have equipped these machines to a sand hopper to inject sand into the slits. This will allow the slits to stay open for a longer period of time and remain effective longer. Using one of these machines perpendicular to the crown on an athletic field may be a way to enhance internal drainage.

Sand Injection

These machines (such as the Dri-ject) have the old Toro Hydroject in their lineage. High pressure water is used to create a hole and the hole is then filled with dry sand or other dry soil amendments (Figure 7). These machines are mostly used on golf greens but larger models are available for athletic field and fairway use. Although these devices do offer some compaction relief, the sand injection is also used to tighten up golf greens after hollow tine aerification. The sand injection also offers a small amount of thatch/ soil organic matter control via dilution. Similar to solid tine aeration followed by topdressing, a hole is being made and filled with material and no material is being removed. Frequent use of this tool without pulling a core at some point should lead to an increase in bulk density. In a Dryject study on athletic fields done at Mississippi State, Drijection five times per season and hollow tining two times per season increased bulk densities compared to hollow tining alone (Craft, 2015).

Slicers and Spikers

These machines produce small holes or slits in the soil in a linear pattern. They do not have much effect on removing compaction or removing thatch. They do create holes and slits that allow the soil to breathe a bit until they are closed by traffic (Figure 8). These machines can be used frequently and there is often little to no recovery time or disruption in play. They are a good tool in the spring transition to do some “venting” and can also be used in the establishment of overseeding. The MSU Campus landscape department has an Aerovator that is often used ahead of fall overseeding. The first seeds to germinate are usually the ones in the holes created by this implement. They are also a good tool to use to open up the canopy. These machines cover a lot of ground quickly and can be used fairly frequently.

To reiterate, hollow tine coring is the backbone of a cultivation program and at least one if not two coring events should take place most years. Make this event a “showstopper.” In addition to the coring event there are many other cultivation tools that are less disruptive and can be used more frequently. If thatch and organic matter are a problem, then vertical mowing or fraze mowing should be considered. If compaction is the main problem solid time aerification or rotary decompaction may be of benefit. Develop a program that works for you and stick to it. The results will be healthier soils and healthier turf.

References

Craft, J.M. 2016. Maintaining soil physical property integrity in turfgrass management systems. MS Thesis, Mississippi State University, Starkville, MS

Carpenter, Matt, 2019. Fraze mowing for overseeding establishment and removal of perennial ryegrass (Lolium perenne L.) MS Thesis, Mississippi State University, Starkville, MS