Left Behind

To leave or not to leave clippings, that is the question. Certainly, leaving clippings is better from an agronomic and environmental perspective. Nutrients are tied up in clippings and when you return them to the turf, you also return nutrients. By returning clippings, you also avoid the problem of what to do with them. Bagging and sending them off to landfills only adds to landfill capacity problems.

However, returning clippings is not always an option. Your site or customers may demand that clippings be collected. Also clipping recycling may not be practical if you have extended the frequency too long due to rain, wet soil or other circumstances. You know best on whether “don't bag it” is an option. To help you in your decision to leave or remove clippings, consider the benefits of leaving them behind.

PROPER MOWING

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Normal, healthy turfgrass growth produces excess foliage that, obviously, must be removed by mowing it — especially as a way to maintain a neat, groomed appearance. The basic rule of thumb for mowing is that you should remove no more than one-third of the leaf blade in a single mowing. Removing more than that could result in damage to the turfgrass and unsightly scalping. As a result, the turfgrass does not produce sufficient photosynthate for root growth and over the long term, it will yield a shallow-rooted turfgrass that does not withstand stresses in nutrition or those caused by lack of moisture or from insects, diseases and weeds. One of the symptoms of an improperly mowed turfgrass is the occurrence of weeds. Proper mowing contributes to a complete coverage of the soil by turfgrass and the exclusion of weeds. Thus, proper mowing is essential for the maintenance of a quality turfgrass.

The optimum mowing height is determined by the turfgrass growth habit and leaf width. You can usually mow a turfgrass that spreads horizontally shorter than an up-right-growing, bunch-type turfgrass. Grasses with narrow blades usually require you to mow them closer than grasses with wider blades. Bermudagrass can be mowed very short because of the numerous narrow leaf blades and the low growing habit. Bahiagrass should be mowed much higher to produce a quality lawn because of its open, up-right growth habit. Suggested mowing heights for a number of turfgrasses are presented in Table 1, right.

Turfgrasses mowed at other-than-optimum heights require special management and more of your attention. Mowing below the optimum height requires production of enough leaf blades to keep the turfgrass dense and healthy. To accomplish this, you will need to apply more fertilizer and water to stimulate growth. Mowing too low can result in a low-density turfgrass with increased weed problems and faster thatch accumulation. Mowing turf too low probably damages more lawns than any other one management practice.

All of this mowing creates clippings, which you must manage one way or another. If the turfgrass you are managing has not been mowed on the regular, recommended cycle, excess clippings may have accumulated, resulting in an unsightly turfgrass surface. However, if you mow turfgrass in a timely and proper manner (at the suggested mowing height), excessive clippings should not accumulate.

CLIPPING DISPOSITION

It's an age-old question: What should I do with my clippings? Should I leave them? Should I collect and dispose of them? Is one better than the other? Obviously, whether you leave or collect the clipping may be decided for you, if your client insists on removal of clipping. However, if the choice is left to you, carefully weigh the pros and cons or removing the clippings or letting them lie. There are a number of issues that you should address before deciding how to manage your clippings, such as turfgrass species, return of nutrients and thatch accumulation. The advantage to collecting clippings: a neat, manicured finished product. The disadvantage: more time and disposal management. (For more information on managing clippings, see “Collecting Clippings,” right.) If you decide to leave the clippings, the disadvantage is that you must mow properly, which may take more scheduling on your part. There is an obvious advantage to not collecting clippings — you save time and avoid creating landfill problems — but there are also some less obvious issues of leaving the clippings on the surface.

  • Decomposition of clippings related to turfgrass species. Research has shown that the leaf blades of commonly used turfgrasses differ in their lignin and cellulose content. These two nitrogen (N)-rich compounds make up the structural components of the turfgrass and their relative presence correlates with the decomposition rate of the clippings of the individual turfgrass. The cellulose and lignin contents of the thatch layer of selected turfgrass species are shown in Table 2, page 14.

    Turfgrasses with high lignin content tend to degrade slower than ones with low lignin content under the same environmental conditions. The data suggest that centipedegrass would degrade slower than other turfgrasses because of its high lignin content. Fortunately, under most management regimes, centipedegrass does not grow as rapidly as, say, bermudagrass, thus does not generally accumulate excessive quantities of clippings. Thatch of St. Augustinegrass contains less lignin than centipedegrass and bermudagrass, thus it decomposes more rapidly. The cool-season turfgrass Kentucky bluegrass contains very little lignin and would be expected to decompose rapidly. In most cases, however, Kentucky bluegrass is grown in cooler climates where decomposition rates are much slower. Therefore, climate may have a greater influence on clipping decomposition than the actual lignin content of the thatch.

  • Turfgrass tissue N content and N released: One of the major potential advantages of returning the clippings is the recycling of the N that exists in the turfgrass tissue. Nitrogen content of the turfgrass tissue varies with the quantity of N you've applied and the growth rate of the turfgrass. Typical values for tissue N content and growth rate of the individual selected turfgrass species are shown in Table 3, page 14.

    Assuming that all of the N in the returned tissue is released and that the active growth period for the individual turfgrasses is 180 days, the potential total N released from the returned clippings could be substantial. At least one third of the recommended N fertilization rate for a highly maintained turfgrass could be obtained from the decomposition of the returned clippings.

    In Central Florida, the recommended N fertilization rate for St. Augustinegrass is 2 to 5 pounds N/1,000 square feet/year. By returning the clippings, you could potentially supply almost 2 pounds of that recommended N on an annual basis, saving you time and money. Tissue N is released slowly over time with very little potential for leaching losses, as opposed to the application of soluble N sources that may contribute to flushes in growth and N leaching in to the ground water, should heavy rainfall or excessive irrigation occur shortly after application. One major additional advantage to using recycled N in the tissue is that it is free. It does not cost extra to return the clippings. In fact you save money indirectly through the reduction in labor for clipping collection and in landfill requirements.

    In a three-year study involving bermudagrass, clipping disposition was studied as it related to the growth, N content of the tissue and the visual quality of the turfgrass. These results are presented in Table 4, page 14. The results of this long-term study suggest that the growth rate, N content and overall visual quality of a turfgrass can be improved by the return of the clippings.

  • Return of nutrients other than N. Recycled turfgrass tissue contains nutrients other than N, which may be beneficial to the overall health and quality of the turfgrass. In the same three-year study on bermudagrass (Table 4, page 14), the influence of clippings disposition of potassium (K) and magnesium (Mg) response was also evaluated. When clippings were returned, no response to applied K and Mg was observed; however, when clippings were removed, a significant response to applied K and Mg was observed (see Table 5, above). Sandy soils typically are low to marginal in exchangeable K and Mg. When clippings are removed, there is a continual depletion of essential nutrients. Turfgrasses growing on soils of low nutrient status may ultimately suffer a deficiency if the clippings are not returned or the marginal nutrients are not adequately supplied through fertilization.

    In this study, when bermudagrass clippings were returned, there was no response to applied K and Mg; however, when clippings were removed, application of K and Mg fertilizers increased growth significantly. Recycling of the nutrients in the clippings eliminated the need for additional K and Mg fertilization, thus producing a higher quality turfgrass without the added expense of supplying these additional nutrients through fertilization.

  • Thatch. Probably your biggest concern relative to returning clippings is the enhancement of thatch accumulation. The general assumption is that if you return clippings, thatch will accumulate and cause problems with turfgrass growth, water relations and decreased overall turfgrass quality.

The good news is that in the South, where warm climates prevail, research has shown that returning the clippings does not result in a significant increase in thatch (see Table 6, page 17). Under warm climatic conditions microbial activity is elevated and the clippings decompose rapidly, releasing the needed essential nutrients of N, K and Mg, as mentioned above. However, research in more temperate, cooler regions of the country has shown that this may not be the case. In one reported study in the Midwest, return of Kentucky bluegrass clippings did enhance thatch accumulation. But in general, in the warmer South and Southeast, return of clippings has not shown to increase the quantity of thatch accumulated in turfgrass.

RETURN ON INVESTMENT

Even though turfgrasses do vary in their composition and apparent decomposition rates, returned clippings from the turfgrasses do decompose in a timely manner and release nutrients. These released nutrients of N, K and Mg can significantly enhance turfgrass growth and quality, saving expenditures for additional fertilization as well as reducing the requirements for landfill space. Returning the clippings, especially in warm climates, does not increase thatch accumulation. If you mow turfgrass properly in a timely manner so that excessive accumulation of unsightly clippings on the turfgrass surface does not occur, there appear to be no disadvantages to returning the clippings, only advantages.

Jerry B. Sartain, Ph.D., is professor of turfgrass science in the Soil and Water Science Department at the University of Florida (Gainesville, Fla.).

Table. 1. Suggested Mowing Heights for Selected Turfgrasses
Turfgrass Species Name Optimum Height (Inches) Frequency (days)
Bahiagrass 3.0 - 4.0 7 - 17
Bentgrass 0.5 - 1.0 2 - 5
Bermudagrass 0.5 - 1.5 2 - 5
Carpetgrass 1.5 - 2.0 10 - 14
Centipedegrass 1.5 - 2.0 10 - 14
Kentucky Bluegrass 1.0 - 2.0 10 - 14
St. Augustinegrass 2.5 - 4.0 7 - 14
Zoysiagrass 1.0 - 2.0 10 - 14

Table 2. Lignin and Cellulose Content of Thatch Layer of Selected Turfgrasses
Turfgrass Species Cellulose Lignin
%
Bermudagrass 3.50 7.00
Centipedegrass 3.33 8.36
Kentucky Bluegrass 4.60 1.78
St. Augustinegrass 1.36 5.94

Table 3. Tissue N Content, Growth Rate and Potential N Release from Selected Turfgrasses
Turfgrass Species Tissue N Content Growth Rate Potential N Released
% lbs/1000 sq ft/d lbs N/1000 sq ft/180d
Bermudagrass 3.25 0.82 4.8
Ryegrass 4.00 0.72 5.2
St. Augustinegrass 2.50 0.41 1.8
Centipedegrass 1.75 0.31 1.0

Table 4. Influence of Clippings Return or Removal on Average Clipping Yield, N Content of Clippings and Visual Quality over a Three-year period.
Clipping Disposition Growth Rate Nitrogen Content Visual Quality
lbs/1000 sq ft/d %
Clippings Returned 1.04 * 3.01 7.1
Clippings Removed 0.82 2.44 6.0
* Values within a column are significantlydifferent at the 0.05 probability level.

Table 5. Influence of Potassium and Magnesium Fertilization and Clippings Disposition on Bermudagrass Growth Rate
Clipping Disposition No K applied K applied No Mg applied Mg applied
lbs/1000 sq ft/ d
Clippings removed 0.82 b 0.98 a 0.82 b 1.02 a
Clippings returned 1.02 a 1.04 a 1.02 a 1.04 a
* Values followed by the same letter within a row are not significantly different at the 0.05 probability level.

Table 6. Effects of Clippings Disposition on Average Percent of Thatch Weight Loss by Ignition over a Three-Year Period
Clipping Disposition Percent Weight Loss on Ignition*
%
Clippings Removed 29
Clippings Returned 33
* Differences not significantly different at the 0.05 probability level.

COLLECTING CLIPPINGS

Walker Mfg., a Colorado-based mower manufacturer, commissioned an independent research firm to conduct a survey to determine how Walker owners and operators handle grass clippings and debris. It's purpose: to identify methods of handling debris, modes of transporting debris, where it's taken, how far and how much, if anything, paid for dumping it.

Nearly 400 owners and operators responded, and these are a few of the results:

  • Nearly 90 percent of all contractors said they pick up debris with their mowers, compared to 2/3 of the other respondents.

  • Midwest contractors are more likely to side-discharge clippings than contractors in other parts of the country.

  • South Atlantic contractors find mulching to be more effective.

  • More than 50 percent of all respondents indicated that the number of properties at which they pick up clippings has stayed the same over the last two years. For those who reported a trend, picking up clippings increased by nearly 3:1 over mulching or discharging.

  • Clippings and leaves are likely to end up in one of two places, according to respondents: either in an on-site or off-site compost facility.

While more than 50 percent reported they are charged for taking debris to an off-site location, less than 20 percent reported disposing of debris in landfills.

Source: Walker Talk magazine, Vol. 19

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