Organic matter management on putting greens is vital for maintaining playability, firmness, and overall turfgrass health. Until recently, measuring and managing organic matter relied largely on assumptions and outdated methods. But that’s changing with the introduction of the new Surface Organic Matter testing method, developed by a USGA committee which I had the pleasure of serving on.
Why Measure Surface Organic Matter?
Surface organic matter, defined as all the living and dead organic material within the top inch of a putting green, can affect putting green performance characteristics including firmness, moisture retention, and susceptibility to diseases and other pests. Historically, turfgrass managers have relied on generic recommendations or intuition to guide organic matter management practices like topdressing and aeration. However, the lack of a standardized measurement method, not to mention the lack of organic matter targets, has made data-driven decision-making difficult.
Introducing the Surface Organic Matter Test
Recognizing this gap, in 2019 the USGA assembled our committee (which included Roch Gaussoin from University of Nebraska, Doug Linde of Delaware Valley University, Jim Murphy of Rutgers University, and Brian Whitlark of the USGA) to develop a standardized method for accurately measuring surface organic matter of putting greens. Through experimentation and analysis, our committee recommended:
- Sampling Intact Cores: Leaving the turf (verdure) intact and avoiding grinding or sieving before analysis, reducing measurement error and keeping the verdure and roots which contribute to the surface characteristics.
- Ignition Temperature: Using 440°C instead of the more common 360°C for igniting samples, providing a more accurate assessment of surface organic matter.
- Sampling Depth and Quantity: Sampling consistently within the top inch (2-2.5 cm) of the putting surface, taking between 5 and 10 cores per green from representative locations.
- Consistent Timing: Conducting annual sampling at the same time each year, ideally before seasonal cultivation or topdressing operations.
Implications for Turfgrass Managers
With this new test, turfgrass managers now have a standardized, data-driven tool to precisely measure and track organic matter accumulation on their greens. This allows for more informed decisions regarding cultivation practices like aeration and sand topdressing. To demonstrate this, we recently concluded a three-year field study on a bentgrass putting green in Wisconsin that evaluated the GreenKeeper App Cultivation Tool in Performance Tracker. Here are some of the key findings:
- Higher annual topdressing sand volumes reduced surface organic matter and soil moisture, but didn’t result in clear differences in firmness relative to lower annual topdressing volumes. Other putting green performance parameters (quality, color, density, growth, shear strength, and green speed) were similar between the high and low annual topdressing amounts.
- The GK Cultivation Tool predicted that after three years of topdressing at the high rate (26 ft^3/M) we could expect 4.3% organic matter in the top inch. The actual result was 4.4%.
- The GK Cultivation Tool predicted that after three years of topdressing at the low rate (14 ft^3/M) we could expect 6.1% organic matter in the top inch. The actual result was 6.2%.
In summary, the highest and lowest sand volumes in our study had significantly different soil organic matter in the top inch (4.4% vs. 6.2%) but those differences did not lead to differences in putting green performance characteristics. The GK Cultivation Tool was remarkably accurate in predicting the impact of topdressing and aeration on surface organic matter. While we did find lower soil moisture in the treatments receiving the most sand annually, this did not result in differences in performance. However, a green with less soil moisture may be less prone to diseases and other pests. This will be the subject of future study. While we still don’t have a handle on the optimal target or ideal range for surface organic matter of putting greens, that goal is now within reach with more research.
Integrating Surface Organic Matter Testing into Your Maintenance Strategy
Using the Surface Organic Matter test, superintendents can:
- Precisely monitor and track changes in surface organic matter year-over-year.
- Tailor topdressing and cultivation practices based on accurate organic matter data rather than general guidelines.
- Utilize prediction tools like GK’s Cultivation Tool to accurately predict how cultivation strategies will influence organic matter levels in the future.
At GreenKeeper App, we’ve integrated the Surface Organic Matter test to help superintendents make better decisions, optimize cultivation practices, and ensure excellent putting green performance. Embracing this new approach allows turf managers to deliver higher-quality greens sustainably and cost-effectively, taking the guesswork out of organic matter management.
