Data-driven decision making is a hot topic at the forefront of modern turf management. One area where this approach is particularly relevant is in the complex world of managing putting green organic matter. Collecting data allows you to track organic matter trends and adjust management practices based on factual information rather than perception. The USGA worked with a group of experts to develop a standardized method of organic matter sampling and testing that helps courses to better understand and compare their putting green organic matter levels.
With a solid baseline of organic matter data, figuring out how much topdressing to apply each year becomes much easier. The goal is to find the “Goldilocks” amount of sand – just the right amount. Applying too much disrupts the playing surface more than necessary and increases costs, but too little won’t keep pace with organic matter accumulation. To help superintendents determine an appropriate amount of sand, researchers from the University of Nebraska conducted a study on creeping bentgrass greens with various amounts of Poa annua. They found that greens receiving annual topdressing rates of 20.3 cubic feet of sand per 1,000 square feet had reduced OM accumulation. They also found that an application interval of seven to 14 days was more effective for managing surface organic matter than making applications once each month (Schmid et al., 2014). This information can help serve as a benchmark application rate, but each course’s needs will vary depending on a range of factors. Unfortunately, most vendors sell sand by the ton, not in cubic feet. So how do you convert cubic feet per 1,000 square feet into tons?
You can start by weighing the sand you plan to use in a known volume to figure out how many cubic feet of your sand would go into a ton. If less math is what you’re after, many use an estimate that 1 cubic foot of sand weighs 100 pounds. This is not the most accurate approach, but it is quick and easy. With that rule of thumb, 20 cubic feet of sand weighs 1 ton. So, the minimum recommended rate based on the Nebraska research is 1 ton per 1,000 square feet per year. Multiplying this by your total putting green square footage allows you to figure out the total amount of sand needed for the year. This provides a basis for evaluating your current topdressing quantities and budgeting. I’ve included an example below for a course with 2 acres of greens:
2 acres = 87,120 square feet
1 cubic foot of sand = 100 pounds (estimate)
20 cubic feet x 100 pounds = 2,000 pounds or 1 ton
1 ton x 87.12 (thousand square feet of putting surface) = 87.12 tons of sand per year
Once you know the total amount of sand you want to apply in tons, it’s easy to budget for the year. You can then calibrate your topdresser to apply the desired amount of sand in each application based on your goal for the year and the number of applications you expect to make. As you track organic matter levels over time, you can see if the rate and frequency of your topdressing applications are keeping up with organic matter accumulation or whether you need to make adjustments. Math may not be your favorite subject, but a little math is worth a lot when it comes to planning!
West Region Agronomists:
Brian Whitlark, regional director, West Region – bwhitlark@usga.org
Ross Niewola, agronomist - rniewola@usga.org
