Topdressing with compost

Traffic is one of the dominant stresses that all actively used sports fields face. Traffic leads to soil compaction that eventually results in a loss of vegetative coverage on primary play surfaces, and unsafe play conditions. Ideally, all maintenance programs are designed to maintain turfgrass quality and coverage after establishment, but more often is the case that turfgrass quality declines as the play seasons progress.

In an ideal world, maintenance practices beyond regular fertilization and mowing will help to improve turfgrass quality, or at the very least maintain it at the original quality. Unfortunately, over time, fields become worn and eventually the quality and turfgrass coverage begin to decline. Fortunately, one tried and true method for mitigating wear damage is to adopt the practice of topdressing and aerification. Topdressing is a time when many field managers will introduce new technology to their play fields, such as overseeding with modern cultivars, or adding soil amendments into the profile. These introductions may help to improve the turfgrass quality and coverage of in-use fields.

Topdressing sports fields with a compost-dominant mix has been a source of controversy, as the typical recommendation is to topdress with materials closely matching the underlying rootzone, as long as the parent material easily drains and is supportive of natural sports turf plant growth. If there were problems with the underlying rootzone material, then topdressing with a relatively uniform sand source that has no fine particles, particularly clay, is the standard recommendation for sports fields.

Extension bulletins often encourage the use of compost in topdressing materials due to compost’s ability to increase the cation exchange capacity of the soil through the addition of organic matter; and to stimulate soil microbe population through the addition of microbes and by creating a conducive environment that encourages microbial population growth.

Research on the incorporation of compost during the establishment period has found that compost additions in general improve both soil properties, such as a soil’s tilth and friability, which ultimately improve soil drainage, as well as increased germination rates. There has been published research on the effects of both compost and compost tea applications on disease suppression in both field crops and turf.

With respect to using compost as a topdressing amendment, the data is limited. One compost topdressing study investigated using compost as the only nutrient source on turf, and two other topdressing studies used manure compost and biosolid topdressing for improving soil structure and improving turfgrass quality. None of these studies focused on Kentucky bluegrass fields that maintain scheduled play throughout the duration of a growing season, like is typical for the northern US states and Canadian municipal athletic fields.

The overall objective of the study performed at the Prairie Turfgrass Research Centre (PTRC) of Olds College was to determine if there were any measurable improvements to turfgrass quality in high wear areas from topdressing with compost. Two compost sources were evaluated: municipally sourced thermophilic compost and vermicompost. Thermophilic compost is the resultant of organic material being broken down into compost through the action of microorganisms during a mesophilic (10-40C) cycle, followed by a thermophilic (40-65C) cycle, and a final maturing mesophilic cycle. Vermicompost is the end product from the use of worms breaking down organic material into worm castings, aka worm manure. Darwin (1881) probably said it best when he was describing the action of worms in their habitat: “It may be doubted whether there are many other animals which have played so important a part in the history of the world, as have these lowly organized creatures.”

Worms create numerous benefits to both the soil and the plants residing in the soil, therefore the use of worm castings as a topdressing material was tested to determine if these benefits of worms could be transferred into a high-wear sports field area. Both compost types were evaluated in this study to determine if one would result in superior performance over the other one.

The topdressing depths tested were: 0.1” 0.2”, and 0.4”, and topdressing frequency was a one-time spring topdressing event versus a three times applications (every 6 weeks) during the growing season. The total volume was premeasured into bags and then hand spread using dustpans and stiff push brooms for sweeping the compost into the canopy. The turf was evaluated weekly for turfgrass quality using the NTEP 1-9 scale, chlorophyll content using NDVI, surface hardness using the Clegg Hammer, moisture levels at the 1.5”, and 3” depths using a TDR moisture meter, and turfgrass surface coverage using digital image analysis (DIA). Soil chemical properties such as Solvita testing (microbial respiration via measuring CO2 output from the soil samples), C:N ratio, and the various soil nutrient levels were measured at the end of the trial through offsite laboratory testing.

Topdressing with either type of compost improved the overall performance of all plots, with the exception of the one-time 0.10” depth treatment. Plots that did not receive topdressing (UTC) had lower performance ratings with respect to visual quality, NDVI, 1.5” and 3” moisture levels, surface hardness, and turfgrass coverage when compared to the plots that received topdressing. Interestingly the 3-season mean moisture levels were lower at both testing depths for topdressed plots, suggesting the addition of compost helped to improve soil structure resulting in greater infiltration rates.

This result was visually apparent in season two of the study (summer 2016), where the research plots were receiving well over an inch of rain each week in heavy prairie-style rainstorms. The compost treated plots did not have standing water while the UTC plots tended to puddle and hold water for several days. The difference between the two compost types was minimal; however, the VC compost did have greater secondary nutrients in the samples at the end of the trial. Unfortunately, worm castings are very expensive and not cost effective for most municipalities to justify using; however the municipally made thermophilic compost did a good job when maintaining turfgrass coverage.

The practice of topdressing with compost resulted in greater turfgrass coverage and quality, although topdressing alone was not enough of an ‘extra’ maintenance practice to improve the quality or the turfgrass coverage beyond the starting point of the trial. Without an overseeding program introducing new plants into the sward, there was a decline in both quality and percent coverage in season 3 of the study, whereas the decline was more apparent in season 2 for the UTC plots.

Maintaining turfgrass coverage is the ultimate goal of high use fields, and it appears that the best strategies for topdressing is to apply compost at the 0.2 or 0.4 in depth one time or the 0.1 or 0.2 in depth three times in a season. Going more frequently resulted in the highest turf coverage, however even just a one-time application did improve turfgrass coverage by almost 20% when compared to the UTC.

The 0.4 in depth may be challenging to achieve, as it tended to leave the plots muddy for a week until the material was incorporated down through the canopy further than the one time manual sweeping action resulted in. This depth was not tested on in-use fields, however the 0.2 in depth was at fields in Calgary, Edmonton, and Lethbridge with play scheduled that same day.

There were no complaints made about the condition of the fields, and interestingly most player groups were happy to see that amendments to their fields were being done. Using compost as part of the maintenance program appears to be beneficial over three seasons, and if the municipality you work in is already green-streaming organics into a local compost facility this may be a great option for improving wear tolerance.

[Editor’s note: references available at]

Katie Dodson, MSc, is senior research scientist, turfgrass, for the Prairie Turfgrass Research Centre, Olds College, Olds, Alberta. By the time you read this she will have started a new job with Syngenta as global technical manager, turf and landscapes, in Switzerland.

Compost topdressing tips

Ensure the compost is ready to use by doing two tests: The Sealed Bag Test: place a handful of the compost into a Ziploc bag, seal it and wait 2-3 days. Open the bag and smell. If you smell a putrid smell, the compost needs to continue maturing before using. If you smell an ammonia smell then the compost source needs the addition of dry carbon material, like leaves added to the pile. Germination Test: do a simple side-by-side experiment using radish seeds where you compare the germination rate of the radishes in potting soil vs. the compost. If germination is limited in the compost pot, it suggests the compost is not quite ready to use.

The texture should be Friable (crumbly) that ideally screened through a 6-9.5 mm (0.25 – .375”) screen.

Moisture content should be 30-50% moisture.

C:N ratio ~30:1

pH 6-8

Apply the compost at 0.2 – 0.4” (0.5 – 1 cm) depth annually or up to 3 times in a season.

Be sure to sweep the material in to minimize any muddy spreading during the following week after application.

Core Aeration is an important part of a maintenance program and should be performed at least once a year in the fall or spring when the turfgrass is stress-free and actively growing.