Topdressing fairways with compost
Using compost on turf is not a new concept. Compost applications were common until the agrochemical revolution in the 1940s and 50s, so you might consider it a "lost art." Currently, there is resurgent interest in using organic amendments and topdressings, as superintendents rediscover the benefits of compost.
Research is confirming what the "old timers" realized long ago. Recently, we concluded a study at The Ohio State University regarding the duration and magnitude of effects of compost topdressing applications to fairway-cut creeping bentgrass/Poa annua stands. We found that clipping yields, color and foliar-nitrogen concentrations were all positively affected for up to 50 days after topdressing with a locally available composted sewage sludge. Other research at Ohio State and elsewhere has documented the disease-suppressive qualities of some composts. Composted material also can improve soil fertility and physical structure.
Additionally, using compost fosters a perception of good stewardship, which is always a plus in this era of environmental consciousness.
An overview of composting Most composts used by the turfgrass industry are produced by piling fresh organic matter such as yard waste, dewatered sewage sludge or poultry manure. Stacking these materials facilitates decomposition by microorganisms such as bacteria and fungi. As these microbes degrade organic material, they generate a great deal of heat. This kills or inactivates many weed seeds, as well as plant, animal and human pathogens (in addition to many beneficial microbes).
As the microbes exhaust the available carbon and nitrogen, the composting process slows and the pile begins to cool. When this happens, other microorganisms, including wind- and rain-borne types, colonize the pile. This final phase of the composting process is the curing stage. During the curing stage, microbes proliferate, including some that are capable of suppressing plant pathogens such as Pythium.
After compost cures adequately, producers typically screen it to 0.25 to 0.5 inch. Then it is ready for incorporation into the soil or root-zone mix prior to seeding, or for use as topdressing.
Many methods for assessing the maturity of compost exist, but no single method provides all the answers. Better guidelines and practical standards for compost are needed.
Setting clear goals The reasons for using compost topdressings are many, but the decision often stems from one of the following factors:
* Compost topdressing is perceived to be environmentally sound. * Composts may serve as an excellent source of plant-available nutrients. * Composts provide valued organic matter and may improve soil fertility. * Some composts suppress turf diseases such as dollar spot and Pythium.
Be clear about your rationale for using compost topdressing. Without a doubt, this practice can benefit turf, but make sure the benefits match your specific needs. Keeping your goals in mind will lead to good decisions about product selection, application and timing, and help you fine-tune your program as you gain more experience with compost.
Our research was the first to define the magnitude and duration of compost-induced fertility effects. Additional research of this sort is needed and should lead to practical guidelines for compost topdressings on fairway turf.
Selecting the right products Once you have defined your goals, the next step is selecting the right compost. This may be easier said than done. A major reason that composts became less popular in the early 20th century is that they were highly variable in their chemical, physical and microbiological characteristics. This has not changed. Even though our understanding of the composting process is improving, achieving consistency with compost still can be difficult. Some composts are more variable than others. To the degree that the parent organic material being composted varies, so will the final product.
The composting process and the consistency and chemical characteristics of the parent organic material are two key factors determining the quality of the final composted product. Additional factors such as the bulking agent (material such as wood chips, sawdust or crumb rubber added to some compost to ensure adequate aeration and pore space during composting), the frequency of turning or mixing and the moisture content of the compost all impact the quality of the final product.
Seasonal variations in the waste stream flow and the weather also may affect compost quality. Consider the differences that exist in yard waste between spring and fall. Grass clippings predominate in the spring and leaves are dominant in the fall. These two materials produce substantially different composts.
The experience level of those managing the composting facility also may significantly influence the final product. More experienced composter suppliers may provide a more consistent and high-quality compost.
Selecting the right compost can be like picking a good wine-it involves some rather subjective criteria. For example, you may have heard that a good compost is dark in color with a crumbly texture, has a moisture content of around 40 to 45 percent and an "earthy" aroma similar to a fertile soil. Though such descriptions are extremely subjective, great value exists in this type of sensory-based assessment. Many workers in the green industry have an intuitive sense for what a rich, fertile soil feels, smells and looks like. Luckily, for those eager to base their decisions on more concrete characteristics (and those short on horticultural intuition), several important physical and chemical qualities are more quantifiable.
* Physical properties. Particle size and texture may be the two most important factors you can use to assess physical characteristics. These properties are important because repeated applications of composts with excessive amounts of bulking agent or similar material might lead to an accumulation of unwanted materials in the thatch or soil.
A glance will tell you whether a compost's texture is suitable for use on your fairways. We typically recommend screening composts for use on fairway turf to 0.25 inch to remove excessive bulking agents and other large components. Even at that mesh, it is difficult to completely remove all unwanted bulking agents. However, the texture should be fine enough to minimize unwanted materials.
* Chemical properties and composting process. Several aspects of a compost's processing and chemistry will provide clues about the material's suitability. Compost suppliers should always be willing to provide you with an analysis for each batch of compost prior to delivery. Hesitation on the part of the producer to divulge this information should cause you to reconsider working with them. This shows why it's important to develop a good relationship with local compost producers.
Ideally, a supplier should be willing to provide the following: - Compost type (parent material) and age. - The composting process they used (static pile, windrow, forced-air static pile or in-vessel). - A complete elemental analysis, including heavy metals (this is especially important with biosolids or municipal solid waste). - Ammonium, nitrate and total nitrogen concentrations. - Compost pH. - Cation exchange capacity (CEC), organic matter and ash content. - Soluble salts (this is of particular concern with animal-manure composts). - Carbon:nitrogen (C:N) ratio.
Additional information regarding nutrient-release characteristics and bulk density is valuable and can help you determine nutrient loading and mineralization rates of the compost. This aids estimating the magnitude and duration of the compost's effects.
Explaining in detail how to interpret and evaluate all this data is beyond the scope of this article. However, you can quickly assess a compost's fertilizer potential by concentrating on pH, heavy-metal content, nitrogen and phosphorus concentrations and the C:N ratio.
The pH of a compost should fall between 5.7 to 7.5, depending on the parent material. Concentrations of heavy metals should meet standards set by U.S. Environmental Protection Agency Rule 503. Nitrogen, phosphorus and potassium analyses in tandem with the bulk density of the compost provide insights about the amount of potentially plant-available nutrients. In general, greater concentrations of plant-available nitrogen (ammonium and nitrate) will provide greater color enhancement and growth stimulation if the compost is applied while turf is actively growing.
High C:N ratios (above 20:1) may indicate that the compost is not fully composted and not ready for use. Immature composts can cause nitrogen immobilization. Microbes require a balanced diet of carbon and nitrogen to decompose organic materials. If a composted material lacks enough nitrogen to facilitate decompostion, the microbes will pull nitrogen from the surrounding environment (such as soil). Thus, if you apply an immature compost, the microbes will steal nitrogen from the turf. The result will be off-color turf that requires additional fertilizer to bring the system back into balance. A good target C:N ratio is around 15:1.
Bioassays are available for assessing compost maturity and turf-enhancing properties, but they are expensive and labor-intensive. Plus, interpreting the results of these tests is often difficult because our understanding of compost microbiology and turfgrass soils is still in its infancy.
Our "bottom-line" recommendation is to base your decisions primarily on physical and chemical characteristics of the compost.
Timing and application strategies Once you've selected a compost, application is relatively easy. The most common strategy is to topdress in conjunction with typical hollow-tine core aeration. This is best performed in the spring or fall when turf growth and recuperative potential is greatest. An additional benefit of topdressing in spring or fall is that daytime temperatures are relatively moderate. This reduces the possibility of burning the turf with "hot" compost (that contains high levels of ammonia or that is warm or hot to the touch) or suffocating the turf with a blanket of compost and aeration cores on a hot summer day.
Whether you core first and topdress second, or vice versa, is a judgment call. Either method can be successful. One advantage to coring first is that you reduce the time the compost sits on the turf. This might be an issue if the weather is turning warmer or you have some concern that the compost could burn the turf.
You can topdress with any device that has the ability to distribute the compost over distances without compacting the soil. Conventional topdressing units designed for golf course use work well.
The rate you use will depend on numerous factors such as time of year, members' expectations, particle size, turf species, height of cut, the nutrient content of the compost and the ability of the turf to assimilate the provided nutrients. We typically recommend a maximum of 1/8 inch of topdressing, which is roughly 17 yards per acre.
Members often are more adamant about turf quality earlier in the season, making a more aggressive topdressing program more acceptable in the fall. A product that has been screened to a smaller size offers greater timing flexibility because it will move into the soil profile more quickly than a poorly screened product.
After you apply the compost, drag the fairways to blend the compost with the pulled soil cores and help move the material into coring holes. You then can blow the remaining tufts of turf and thatch into the roughs, where a bagging mower will easily pick them up.
The final step in the application process is to irrigate the fairways as soon as possible. This reduces turf stress and the potential for ammonia or thermal burn, or heat-induced stress.
Keeping records If you apply compost topdressing, it's useful to maintain records that document physical, chemical or biological properties of the compost. Also, keep financial records so that you can perform a cost-benefit analysis. Application records that include timing, a description of the actual application process, weather data, soil temperatures and moisture levels can help you correlate good or bad results with specific application techniques or environmental conditions. Make and record follow-up observations to document the magnitude and duration of the effects of the compost. And don't forget to take note of membership comments and concerns.
Good documentation is important for future reference and decision-making. Accurate records allow you to fine-tune your program for maximum benefit, as well as compare your compost topdressing program with standard topdressing practices to assess the value of using compost.
As with any new management practice, use common sense and take a conservative approach at first. Try topdressing with compost on a small scale and evaluate the effects before applying it to every fairway. Consider including a non-treated area (no coring or compost) as well as an area where you core but don't topdress to assess the effects of your program. Without such control areas, it is impossible to assess your practices with any precision.
Dr. Mike Boehm is assistant professor of plant pathology and Dr. Joe Rimelspach is extension associate for turf, both at The Ohio State University (Columbus, Ohio). Dan Garling is a former graduate student of Ohio State's turf program and currently works under Dan Dinelli, CGCS, at North Shore Country Club (Glenview, Ill.).
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