Monday, 17 December 2018

Turfgrass Speedo

How fast should we grow our grass? It's a question I have been asking on this blog for almost 7 years now and every year I think I get a bit better. I explained this evolution last year in a blog post called "The Evolution of Precision Fertilizer Application."

Image result for grass speedo
No, not that type of speedo Source:
Even as I progress I still admit I have absolutely no clue what I'm doing when it comes to driving turfgrass growth. There are many clues as to the ideal growth rate. I wrote about that in a post called "
Using indicator species to fine tune fertilizer applications."

Could a tool like this help me grow grass at the right speed?
Basically, I have this feeling that achieving the optimum growth rate will make a lot of our issues less severe but figuring out what that speed is has been a challenge. Every year is different so what worked this year certainly won't work next especially if you are looking to really fine tune things to an extreme degree like I have been playing around with.

Tools like the growth potential have been a big help but again, they don't tell me how fast I should grow my grass.

Clipping volume has been a tremendously useful tool to understand the health and vigor and differences in how my grass grows. It has given me clues that growth rates matter. But again, I still don't know how fast I should grow my grass.

At times I require a lot of fertilizer to get the grass to grow and at other times it grows much faster than I would like despite applying hardly any fertilizer. 

Here's the thing. Growth doesn't just rely on how much fertilizer you apply. Adding nitrogen fertilizer can do one thing, make grass grow faster.

Sure we can use growth regulators to grow the turf slower but I also wonder that if we are acutely aware of how fast our grass is growing then why can't we grow it at an appropriate speed without having to spend more money putting the brakes on?

The can of worms opens wider. What is an appropriate growth rate? It depends! How much traffic do you have. Do you want to manage for playability first or plant health first? Every course is different so no one can make a generalization on how much nitrogen to apply.

You start to see why I am so confused with this. There is simply so much we don't know about things as simple as how fast we should grow our grass because it is such a difficult question. I do think, however, that it's a question worth looking into and trying to solve. The benefits of getting it right all the time could be huge.

While working on a presentation about precision fertilizer use for the greenkeepers in Denmark last month I thought of a new way of using the clipping volume and growth potential tools to potentially give me better insight into how fast I should grow my grass.

What if we combine growth potential with #ClipVol ?

Just like I have used growth potential to estimate how much nitrogen I should apply in the past we can use it to estimate how much grass we should grow and it's actually pretty easy especially if you use my turfgrass weather modeller

We simply multiply the growth potential by the maximum growth rate we would ever want to see on our course.

Say the maximum amount of grass you would ever want to harvest in a month is 500ml/m^2. If the monthly growth potential was 50% we would expect to harvest about 250ml of grass/m^2 that month.

That's all fine and dandy but that still doesn't help us know how much fertilizer to apply.

What if we compare the ideal amount to the actual amount. So if we wanted to grow 250ml of grass but we harvested 400ml that would be 400/250 = 1.6. Basically we are growing the grass 1.6 times too fast and we need to back off on the nitrogen fertilizer.

We can compare this number over any time period and it's a feature I added to my Turfgrass Maintenance HUD recently.

Below you can see that addition. On the upper chart you can see the monthly clipping yield compared to the ideal yield. The absolute value doesn't matter. What matters is how close to the ideal amount you are. Generally I've noticed that the further I am from the 1 or yellow line, the more conditions suffer. This chart can also show you when what you are doing to push growth is working even though it might not seem that way. In March 2017 we were recovering from winter damage and even though growth was slow, you can see it was WELL above normal. The extra fertilizer and tarping worked!

The lower gauges compare the actual vs ideal growth rates over varying time frames and could possibly help me make better decisions on how much I need to push or slow growth. We haven't mowed this month yet so obviously there is no recent data. Last month I grew that grass too fast and had some issues with microdochium. But over the last year I grew that grass almost perfectly overall. There were peaks and bumps in the road that certainly caused some issues but overall it was a good year.

The new superintendent here also noted that the greens were really nice and green. They might look nice but there's a cost to that colour in December!

Lush greens in December can be a problem
To determine the weekly ideal harvest we would divide the monthly maximum by 4. Daily by 30.5 etc and compare it to the actual yield.

If we are going too slow we can add more fertilizer, if we are going too fast we can apply less. I think there might be value in having an awareness like this.

The monthly maximum will vary from course to course. I came up with a monthly max of 625ml based of my historical data.

Anything more than that is excessive and actually achieving that level should be impossible because no 30 days in a row are exactly at 100% growth potential. Of course we could go higher if growth rates explode like they did last summer.

You can use monthly yield data to determine how much is too much. Last August was way too much but July was just about right for my course's specific needs.

This gives you a hypothetical turfgrass growth speed limit and shows how fast you are going compared to the limit you have set for yourself adjusted to the actual weather conditions. Nothing is based on the date on the calendar but more on actual growing conditions. Then if you feel growth rates are too high you simply adjust the monthly maximum number and this will adjust across all your data.

The amount of nitrogen we apply doesn't really matter. What matters is results. What matters is growing the grass at the appropriate speed and I have a hunch that this might be the best method yet of figuring it all out and achieving better results more consistently but I don't know, it's winter and I have 4 more months to go before the grass starts growing again. As usual I am already excited for next season's grass growing.

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