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Does size matter?

When you make a fertilizer application, do you calculate the rate using the size of the greens, or the size of the area the fertilizer was applied to (spray area)? Unless you have a super high tech GPS sprayer with individual nozzle control, you likely also fertilize some of your green surrounds, collars and approaches when you fertilize your greens. This isn't a bad thing and can actually have a bunch of benefits. I talked all about this in a recent post where I discuss precision and whether or not it is actually useful or not on a golf course.



Let's pretend my greens are 1ha in size and I apply one 25 kg bag of urea to that area. The rate would be 1.15g N/m^2 (25,000g urea x 46% N/g urea / 10000 m^2/ha = 1.15). If we include the overspray the area we applied fertilizer to turns to 1.2 ha. This changes our application rate to 0.96g N/m^2 which is 17% less! 17% is a pretty big number especially when spread out over a year.

I have seen some examples with turf software where you cannot tell the database how big of an area you actually applied the fertilizer to. Instead, you are stuck with the actual size of the putting greens. This is a big problem.

Of course, we all learn about this in school. I think the number that was used when I was in school was 15% or something. We need to ensure that we have a bit extra in the tank for overspray. The difference is how we do the calculation in our records.

The amount of overspray is easy to calculate if you have a modern sprayer. Spray the greens and read out the size of the area you just sprayed. Subtract the size of the putting green surfaces to figure out what the amount of over spray is. In the example above the size of the overspray is 2000m^2.

It is more difficult to calculate if you are using granular fertilizer though. Instead of reading a computer screen to determine the size of the area you applied the fertilizer to (assuming you calibrated your sprayer correctly) , you need to work backwards using your application rate and amount of product applied.

Let's pretend you again have a 25kg bag of urea that you are (foolishly) applying as a granular to your greens. Yikes! (The rates described here are perfectly safe to apply even in relatively high heat when dissolved in water, when applied as a granular, the concentrated particles might burn unless you water it in like crazy and use a fertilizer with a very small SGN)

You calibrate your push spreader to apply 2 grams of fertilizer per square meter which works out to 0.92 g N / m^2 ( 2 g / m^2 * 46% N / g urea) . You go out and fertilize the greens and at the end you have 1.2 kg of fertilizer left over. This means that you just applied 23.8kg of urea to your greens (25kg - 1.2kg = 23.8kg ). That is 23800 grams of fertilizer. That means you applied that fertilizer to 11900 m^2 ( 23800g / 2 g / m^2 = 11900 m^2 ). This means that your overspread is 1900 m^2.

It's a bit more complicated than that because granular spreaders don't apply the product evenly across the width of the particle spread. Instead, you overlap to get "uniform" coverage. The outside overspread, will therefore be at a half rate on the sides of your application area, and somewhere between a full dose and a half rate on the ends (have I mentioned I don't like granular fertilizer?).

For me, I much prefer calibrating a sprayer vs a push spreader. There are just too many variables involved with a push spreader such as topography, fitness of the applicator etc. A machine is much more consistent although never absolutely perfect. A sprayer is much more precise (some might say, too precise haha).

The same is also true for chemical applications. You need to make sure that your application rate for each chemical is measured for the size of the total spray area and not just the size of the greens or tees or fairways etc.

When it comes to clipping yield, use the exact size of each playing surface because you shouldn't normally have overcut haha!

There are many areas where it is virtually impossible to fully calculate how much fertilizer was actually applied unless you use a GPS based system that can map the various rates and calculate the total applied over time for a specific location. I don't think we currently have this capability so I just focus on the areas that have clear boundaries. Greens, Tee, and Fairways. I am very sporadic for rough fertilizer and only make applications based on how it looks. Areas with high traffic get fertilizer, areas with massive growth and clippings, don't. Even then, I can still look back and see what my rates were for these extra areas or areas of overlap and get a good idea of what the annual total might look like. Regardless, the data is far from perfect but that's ok.

It's also important to remember that the grass actually doesn't care how much fertilizer you just applied as long as it's not too much which can cause burning. If you apply 1g N / m^2 or 0.92 g N / m^2 it really doesn't matter. What matters is that you are applying fertilizer to get more growth when it is needed. If you need more growth, apply more fertilizer. It's not that complicated.

Avril knows fertilizing turf isn't complicated, do you? hahaha

If you are using your own spreadsheets for your fertilizer records or are using a high tech software solution, make sure that you are able to record you fertilizer and chemical applications based on the spray area and not just the size of the specific area you are sprayer.




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