Tuesday, 13 June 2017

Extreme Growth Rate Turfnerdery


Measuring the clipping yield has been one of the most enlightening things that I have done in the past 6 years. Knowing how the grass is growing is a super important metric in my opinion. Pretty much everything we do depends on grass growth and with the tightening of budgets gone are the days when we could just guess at how we grew our grass. Ideally, we want to grow the grass only as fast as is required to handle the wear and tear of golfer traffic. Anything more wastes labor, fuel, and results in less consistent playing conditions.

This is very similar to what agriculture does. They measure yield, and make adjustments to maximize it. For us, it's a bit more complicated in my opinion because we aren't simply worried about maximum yield. We want optimal yield. Not too much and not too little.
Clipping Yield on Greens, chart made by Micah Woods.

It's kind of puzzling to me that more people don't measure clipping yield and it is also interesting that more research isn't being done on the impacts of different growth rates. If we know how our grass is growing we can fine tune our fertilizer applications and possibly reduce mowing and cultural practices like aeration and topdressing. How the grass grows has impacts on literally every part of maintaining a golf course. If we are guessing, we are probably wasting resources and settling for less than ideal conditions.

Just like how the STIMP meter is a way to measure the cumulative effects of everything that impacts green speed and smoothness, measuring clipping yield is a great way to measure the cumulative effects of everything that impacts turf growth and health. Just like with STIMP, we strive for consistency from green to green and I think that we should also be aware of the inconsistencies of how our grass grows (or mower sharpness or things that impact yield) so that we can make better decisions on how we maintain our course across the varying micro-climates. It could also help explain disease issues that arise that are related to turf growth.

One of the ways we can measure clipping yield consistency is to use the coefficient of variation. Micah Woods described how he measured this variance in a blog post from last year. Basically you take the standard deviation of your clipping yield numbers, and divide it by the average clipping yield for the given day that you collected the data. The advantage of this method (so I'm told because get real, I'm no statistician or Chief Scientist) is that it identifies the outliers so that you can see which greens are out of whack. I measured the clipping yield on my greens the other day, check it out;

Hole NumberArea (m2)LitersLiters/100m2
128062.14
2312185.77
3291186.19
4326154.60
5289.7124.14
6350.892.57
731013.54.35
8375.392.40
9445.5122.69
LP2007.53.75
UP19531.54
Average3.65
Most recent reading date6/12/2017
Recent day average3.65
Recent Day Coefficient of variation0.4152449349

First things first you need to figure out the clipping yield per unit of area. I use 100m2. This standardizes the data so we can compare it. We can then calculate the coefficient of variation (Cv) easily. As you can see, our Cv is 0.41 which I would consider rather high. Figures that are shaded green fall within the Cv. Those that aren't, are way off!

This is because we have had to manage the growth on our greens differently due to winter kill on a select few greens. Can you guess which greens we have been pushing recovery on? I'll give you a hint. There were 5 greens with winter damage. Three of those greens received supplemental fertilizer until 1 month ago, two of those greens received supplemental fertilizer until last week. One of our greens has had some irrigation issues. Can you figure out which one by looking at the clipping yield? Can you figure out which one is which by looking at the following pictures?





If I was guessing based on how they look I would think they were all the same, but as you can see, 2 of my greens are growing 2.4x as fast as my undamaged greens. That's a big difference.

So what does this number mean? Essentially, the lower the Cv, the more consistent the clipping yield is. According to wikipedia, any Cv over 1 is really bad. So what is good? Well I know a guy that is looking into this so I will let him share that when he's ready but until then I can share the Cv of my greens that are managed consistently.

If we take my greens that didn't receive damage last winter and have only received their regular fertilizer applications based on the MLSN and growth potential, we get a Cv of only 0.03. That is very consistent! If we compare the greens that received supplemental fertilizer until 1 month ago you get a Cv of 0.07. That is also very low and shows to me that greens that are managed consistently grow consistently.

Now that the greens are more or less recovered I want to know how their growth rates are different. How long will the impacts of the higher fertilizer rates last? Knowing that they are growing differently could help me understand any issues that may or may not arise in the future.

Measuring the clipping yield on every green every time you mow might be crazy and isn't required to calculate the coefficient of variation. All you need is the clipping yield for every green on any given day. My plan is to measure the clipping yield on all my greens maybe once a week and maybe once a month after things stabilize. I will continue measuring the clipping yield on my 2 standard greens so that I can calculate the relative growth rates and manage my greens accordingly as a whole. In order to calculate growth rates you need to measure at least 1 green (the same one each time) every time you mow.

I'm not the only one that that thinks we need to only measure one standard green each day to get a good picture of everything, but I think that just like STIMP, it might be important to also measure all the greens every now and then though.

We further make it easier to measure by only collecting the clippings from the center basket on our triplex mower. Recent data collection shows that our center basket collects 33% of our yield (surprise!) so we can just multiply our yield by 3 to get total yield and save time measuring clippings. This can be seen in the table below.


HoleLiters of clippings CenterLiters of Clippings totalArea m2Center basket ratio
12728028.57%
261831233.33%
362029130.00%
451432635.71%
5411289.736.36%
639350.833.33%
74.513.531033.33%
8310375.330.00%
9412445.533.33%
LP2.5820031.25%
UP12.519540.00%
TotalTotalTotalAverage
411253375.332.80%

Naturally, I created a google sheet and form to make collecting this data easy using my smartphone in the field. You can make a copy of and see it here. Our daily clipping collection data is collected on our equipment use form as it always is so that we require minimal effort to collect this information. If it's not consistent, it's not useful. This data is also updated in real time to my job board so that I can see how consistent our clipping yield and stimp readings are.


Course Data
Growth Rate mL/m2/dayGrn Rolls43
Day12.5Grn Mows35
Week10Roll/Mow Ratio1.23
Month8.50STIMP8.5
Yield CV41.52%STIMP CV5.14%

As I mentioned, the time it takes for my greens that have received supplemental fertilizer to fall within the Cv and the time it takes for the overall Cv to return to the levels found on my undamaged greens is interesting to me. I will be measuring the Cv this summer and will share the results when the growth stabilizes.