Beyond the Stimpmeter

by Dr. Micah Woods

Tru-Firm testing on a green.

In my work I have the chance to use different measuring devices and meters to measure various turfgrass performance characteristics. Every golf course superintendent is familiar with the Stimpmeter, and probably has one at the course. Here is some information about three other types of meters that golf course superintendents may find useful.

Chlorophyll Meter

The CM-1000 is a meter from Spectrum Technologies that measures the chlorophyll index of the grass. I think this is an especially interesting device because it gives a reading that tells us two very useful things. First, the chlorophyll index reading on the CM-1000 is basically the color of the grass — how green are the leaves? And because golfers care about the color of the grass, using of the CM-1000 allows the superintendent to measure the color and to determine how different maintenance practices may influence the color of the grass. And this chlorophyll index is more sensitive (and more accurate) than what I have been able to see with my eyes. Dr. Larry Stowell at the PACE Turf Research Institute in San Diego did some testing a few years ago with applications of iron to grass, and the CM-1000 meter was able to measure color differences from the iron applications more accurately than what was visible to the human eye. In some grass evaluations at Hong Kong, I have seen that the CM-1000 is able to measure the color difference between different grass varieties, and also has measured the changes in grass color as influenced by the weather which leads to the second very useful thing that I like to use this meter for — we can use the chlorophyll reading as an index of the grass health.

If we take any two grasses, usually the one that is greener is going to be more actively growing and is going to be healthier. So if the grass chlorophyll index starts to decline, this meter can detect the decline before we can see it with our eyes. What influences the grass color? Some of the main factors would be nitrogen, soil moisture, mowing height, and traffic stress. These factors that influence the grass color (and health) can be managed more precisely if a CM-1000 is used to monitor changes in the chlorophyll content of the grass.

Soil Moisture Meter

A digital soil moisture meter can be an especially valuable tool. I have made use of these devices to determine the soil moisture content and then used that information to help with irrigation scheduling decisions. The wilting point of grass will depend on the soil type at any individual golf course, but we can expect that at about 10% volumetric soil moisture content, the grass may be close to the wilting point. After a heavy rainfall the soil soil will be at field capacity, and that may be somewhere from 30 to 40% soil moisture content. Again, the amount of water in the soil after a rain will also depend on the soil at your course.Basically, we have soil moisture that will range from about 35% when wet down to about 10% when the soil is quite dry and close to wilting. When we use a soil moisture meter, we can determine where our soils are on that gradient of soil moisture, we can identify where the dry spots are before we can see them with our eyes, and we can apply water more precisely than if we did not have such a meter. I have used three different models that all work well, although if you have salinity problems, you won’t want to use the Field Scout TDR meter, as salts in the soil can cause errors in the soil moisture readings with that meter. Here are three meters that I have used:

  • Hydrosense from Campbell Scientific
  • ThetaProbe from Delta-T devices
  • Field Scout TDR-100 or TDR-300 from Spectrum Technologies


The Tru-Firm is a new meter that is designed to measure the firmness of a golf playing surface. It is probably most useful on greens, but can also be used in bunkers to determine if fried egg lies will occur, and the meter can be used for fairways and approach firmness measurements as well. There have been a couple articles about the Tru-Firm in the USGA Green Section Record and there was an article about it in the New York Times during the US Open this June; the Tru-Firm is available for purchase from the USGA and was developed by Dr. Matthew Pringle, senior research engineer with the USGA. Dr. Pringle usually tests golf clubs or golf balls, and not turfgrass, but the Tru-Firm is a really interesting device.

It involves the dropping of a cylinder with the end shaped like a golf ball onto the ground, and the meter records exactly how far the cylinder penetrated into the ground. Basically it measures how deep the ballmark is. This is not a meter that is needed at every course, but I think for courses that host professional tournaments, the Tru-Firm would be a very useful tool. Maintenance practices such as irrigation, rolling, aerification, verticutting, topdressing, and even mowing height can have an impact on the firmness of the playing surface. Using the Tru-Firm can help a superintendent manage the playing surface by measuring how the firmness changes with different maintenance activities.

These meters are not for every golf course, but for some facilities these meters would be useful in the management and scheduling of maintenance activities, with the result being a more consistent playing surface. By carefully monitoring the leaf chlorophyll and the soil moisture, it may be possible to slightly reduce the irrigation and fertilizer inputs too. And that could save some money, which is important because the meters are not cheap. The CM-1000 is about $3,000, the soil moisture meters are approximately $1000 or more, and the Tru-Firm is almost $9,000 (like I said, not for every golf course!).

Dr. Micah Woods ([email protected]) is the Research Director of the Asian Turfgrass Center (

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