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| It wasn't the easiest year for growing grass, but the conditions were still pretty good. |
Almost 4 years ago exactly, I came up with the idea of comparing actual clipping yields to the "ideal" clipping yield or the clipping yield adjusted using the Growth Potential Model. Since then, it has proved to be a much more useful tool to manage growth than I originally thought.
It has been almost a decade since I started making observations on plant health and playability and how it relates to the clipping yield. I have been constantly searching for ways to get the growth rate right as often as I can and this tool seems to be the best way I have seen so far, and might ultimately, be the best way going forward. To prove this point I will discuss in a future post, the success I've had with pest control in the past few years (for the most part (Not withstanding the times where I think my greens are dead but they actually aren't...thanks T)).
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| Never needed less |
There are many predictive models already developed or currently being developed to help turf managers manage the growth of the grass. GDD (growing degree day) models have made a huge impact on how turf managers time plant growth regulators but ultimately, they are tools designed to manage growth that don't take actual growth or site specific conditions into account for the person using the model. Yes, growth was considered when developing the model but are not used by the end user.
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| Clipping Yield by itself isn't as useful as comparing to to a weather-adjusted target |
The turfgrass speedo/growth ratio only takes actual growth into account and compares it to the "ideal amount" of growth.
I've often struggled with growth rates that are too low during the summer. This leads to disease issues like anthracnose and issues with excessive wear and tear. I've also been a regular user of PGRs and GDD models. My problem was that I was using 2 different models to manage growth, GDD and the speedo, but these two models were not working together to achieve the end goal which is growing the grass at the right speed.
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| Bentgrass filling in an anthracnose scar. |
It's totally idiotic once you look back at it. An example will be this summer right before I realized my idiocy. The chart below illustrates this.
The blue line is the 30 day speedo/growth ratio and the closer it is to 1, the better (in my experience). As you can see it is trending downward and to a point that is too low in my opinion. The pink line is the PGR elapsed GDD. It goes back down to zero when a PGR is applied. The blue bars are nitrogen applications in g N/m^2. Nitrogen applications should make the speedo go up. PGR make the speedo go down. Early in the summer I let the PGR interval go much beyond the recommended 205 GDD for Primo and the growth ratio responds by starting to trend upward. After a few weeks of trending very nicely just below the "target" I get trigger happy and start applying PGR below or exactly at the 205 GDD. The Speedo goes down and I respond with increased fertilizer applications. What I should have done is extended the PGR interval AND increased nitrogen applications. I was applying too much PGR for my intended growth rate. I was doing it correctly in the early spring, then shit the bed in mid Summer.
It might be important to remember that at this point I am seriously micro-managing the growth rates to a similar degree that turf managers manage quality of cut. We still had pretty good growth, just not as high as I wanted. The differences were small but small differences are what make good grass GREAT grass. The grass wasn't growing so slow that it was dead or dying, we were still able to meet or exceed our playability goals every day. I just wanted better and figured I could get better with a slightly higher growth rate, sue me.
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| Despite lower than ideal growth rates, the greens were awesome. I just thought they could be better with slightly more growth. |
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| Greens speeds were on target except when growth dropped too low. I'm not sorry. |
It finally dawned on me, my problem was that GDD wasn't reality. Reality was what I was actually cutting each day. My model suggested I grow the grass faster so instead of applying PGRs on a GDD interval, I should apply PGRs when growth was too high compared to the turfgrass speedo/ratio.
No shit captain obvious.
So I am not going to use GDD to apply my PGRs next year. I will still track them to see what my reapplication interval is, but will time them to get my growth ratio as close to my target as I can. If growth is too high, I will decrease the interval and maybe increase the rate. If growth rates are too low I will withhold PGRs and increase nitrogen rates.
I think that an approach such as this makes other predictive models redundant but gets the job done with a lot less complication. The speedo model is really good but not perfect. It doesn't have to be perfect because it is just designed to suggest the ideal growth. You are free to manage the growth curve on whatever side of the curve you want. Maintain your growth rates above normal if you need recovery and below normal if you want more anthracnose haha. Other models using AI and machine learning overcomplicate the intent of these models and probably won't result in much improved conditions, not until we can manage fertilizer and growth rates on a micro (square meter) scale and even then, is it really worth it?