Monday, 9 July 2012

Moisture Meter and Distribution Uniformity

Testing VMC on putting greens.
Well the weather is finally dry enough that we are again using our TDR 200 moisture meter on putting greens. It has been a week without rain with temps in the mid to high 20s and we still have over 30% Volumetric Moisture Content (VMC) in our greens. Normally we aim for about 20-25%. We hope that in the next few days the moisture levels drop even more and we can really firm up the greens.


Five years ago before we had a moisture meter on the golf course we did an irrigation audit on our putting green irrigation systems and found that on average we had about 45% Distribution Unifromity (DU) efficiency. At best you can expect to get about 70-80% on most good systems and we fell well short. This poor efficiency and the fact that we were essentially guessing how much moisture in our putting green soil made if very difficult to irrigate our putting greens.

We decided that the best course of action was to upgrade our old outdated irrigation system to a state of the art system. We completed 5 holes over 2 years until the economy took a dive. We were then forced to put the upgrade on hold.
Our first moisture sensor. They didn't
last a month.

4 years ago we got our first moisture meter. It was designed to be permanently installed into the putting greens but we used it as a hand held unit and hammered it into the soil to get readings. It was a real cumbersome process but we made it work. Eventually the sensor would be destroyed from the constant hammering into the hard soil. Finally we got a TDR 200 sensor which is specifically designed to be repeatedly stuck into the soil to take readings.

For the first few years we monitored moisture levels we would use it to adjust the automated irrigation system to get the most uniform distribution. This was a real challenge and we were constantly making changes to the scheduling which was a real pain in the ass.

Last season we changed our approach. Instead of watering our putting greens daily to keep a constant VMC we would give the greens a good soaking. We would then monitor the moisture levels in the greens over a few days. We would hand water any spots that dried quicker than the average. When the overall putting green average VMC dropped below our trigger number (20%VMC) we would start the cycle all over again. Where we used to irrigate daily we now irrigate 1-2 times a week using the automated system. This way of irrigating has less reliance on the DU of your irrigation system and more on the percolation and water holding capacity of your putting green soils.

In most cases it is far easier to get a uniform soil than irrigation system DU especially when wind comes into play. We have fantastic wetting agents available these days that allow for uniform water movement through the soil.

Watering deep and infrequent also helps draw air into the soil as it is allowed to partially dry out in between irrigation cycles. This in turn allows for deeper rooting which in turn allows you to push the number of days in between irrigation cycles. Drier greens are also less susceptible to fungal diseases.

Now anyone how manages Poa might say that you must water daily to keep it alive during the hot dry season. I disagree in most cases.

  1. Match your probe depth to the depth of your roots. This allows you to know how much moisture is available to the plant. There is not point in measuring how much moisture is below the roots. If your roots are 1" long then get 1" probes. Measure the VMC and see if you can get away with watering less.
  2. Wet poa is dead poa when it gets hot. Every hear of Anthracnose? For this reason we never apply any water to our putting greens after 10am. We want the green canopy to completely dry out in between irrigation cycles. For this reason we have never ever had a problem with Anthracnose.
  3. We do not syringe our greens ever. We have found that the surface cooling effect is minimal and not worth the risk of high humidity and Anthracnose. Keep that canopy dry!
  4. If your plants are using up all the available water in the soil each day then you must water daily.
You will really be surprised how long you can go without irrigating your putting greens but you MUST know exactly how much moisture you have in your soils for this to work. Simply turning off the system is dangerous. 

When we used to water to keep the moisture levels constant it was dangerous. We were constantly a day away from disaster. If the system failed to come on one night we could risk losing turf. This way of watering also encouraged the growth of Poa annua and who wants to do that? It was very very stressful. Now I can see it coming. Our greens are dry, firm, and way more consistent than they have ever been. We are also seeing bentgrass come on really hard this year. Coincidence?

Back to the DU of our remaining 4 greens that didn't see the upgrade. To tell you the truth we don't need it any more. When we irrigate, we water to field capacity or a little higher. The soil then takes care of the water and after a few hours the soil moisture levels are pretty constant in the soil. Call me crazy but I am seriously considering installing quick coupler heads in the future. It is cheap, low on maintenance and it makes it really hard to over-water your greens. Especially when you are lazy like me.

In the one season that we have changed the way we water I have seen our root depth double. This despite that for 10 months a year the weather is incredibly wet. Take advantage of the warm weather and use it to grow out some roots. You will need them when it gets hot.

So the way I see it there are two ways to use your moisture meter. You can use it to see when you need to water, or you can use it to see when you don't need to water.