CDC 2787 Soil Test

Learn how improving your soil can lead to a better looking lawn
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cdc2787
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CDC 2787 Soil Test

Post by cdc2787 » April 14th, 2021, 8:53 am

Hello, my lawn is approximately 18,000 sq. ft. and without irrigation. Last season I followed (most of) the recommended plan from my previous soil test that is linked below. The additional cost of ferrous sulfate scared me off, but I'm going to bite the bullet this year...assuming it gets recommended again. I would like the best approach as well as a nitrogen recommendation. Thank you in advance for your assistance.

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andy10917
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Re: CDC 2787 Soil Test

Post by andy10917 » April 14th, 2021, 8:59 am

Put a link pointing to this thread into the Soil Test Interpretation Queue

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Re: CDC 2787 Soil Test

Post by cdc2787 » April 14th, 2021, 10:16 am

Andy, I'm wondering if I overcomplicated my math for your ferrous sulfate recommendation, from my 2019 test, and that would explain how I came up with such a high cost. When you recommend 2-3 lbs/K of Ferrous Sulfate is that what you asking straight up or am I looking to apply 2-3 lbs/K of Iron?

The product I was looking at is 20% Fe and comes in 50 lbs bags, so 0.2 X 50 lbs = 10 lbs of Fe per bag.
2 lbs of Fe per K, with an 18,000 sq. ft. yard means I would need (18,000/1,000)x2= 36 lbs of Fe per application.
One bag contains 10 lbs of Fe, meaning I would need 3.6 bags per application.

...or is it as easy as I need 36 lbs of Ferrous Sulfate per application? I must have read your 2019 recommendation at least 10 times and only questioned my interpretation yesterday.

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andy10917
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Re: CDC 2787 Soil Test

Post by andy10917 » April 14th, 2021, 10:49 am

Nope, it's simple - no math. 2-3 lbs/K of Ferrous Sulfate - not 2-3 lbs/K of Iron.

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Re: CDC 2787 Soil Test

Post by MorpheusPA » April 16th, 2021, 9:06 pm

I like the development here (this isn't your first rodeo, so I'll simply hit the high points, Andy's covered you nicely in past tests). Mostly, your soil has evened out beautifully.

That very minor calcium shortage is not a problem and will probably disappear on its own (or grow a bit, we'll see) depending on whether more perks down or some washes out. Either way, your pH is now perfect and calcium, magnesium, and potassium and in great ranges.

Phosphorus is pretty much perfect as well, with a target of 200, and you have about 25 to play with. That's great.

I'm going to carbon-copy Andy's micros from 2018, it hasn't changed: "In the micronutrients, Boron is short and has interactions with Calcium. Both being short is not optimal. Get and apply Twenty Mule Team laundry soap from the grocery store, and apply it at 3 tablespoons/K as outlined in the Micronutrient Application Guide every 60 days. BTW, your Manganese numbers are high enough to open a Manganese mine. Manganese and Iron have a complex relationship and I'll keep an eye on that for you."

Although both are no longer short, I'd really like to see boron come up more. Target is 0.7 and while 0.4 isn't absolutely horrible, it would be nice to see closer to 0.6 or so.

That iron/manganese thing is still going on, so doing the boron tap will also add iron to your soil to help with the iron ratio as well.


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andy10917
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Re: CDC 2787 Soil Test

Post by andy10917 » April 16th, 2021, 9:27 pm

Chris, there isn't a whole lot to do. The structure is a little sandy, the cations ratios that lead to the pH is a bit in the side door. But nothing other than the Iron you skipped is calling for attention - address it.

For a Nitrogen source, use a fertilizer that has Nitrogen and Potassium (N and K but no P) - this will close the small Potassium shortage with extra effort.

I'm not adding additional items, as if Ferrous Sulfate breaks the budget for applications, then everything I can think of is off the tablem.

In the micronutrietns, Boron is short. Get Twenty Mule Team laundry soap and apply it at 3 tablespoons/K every 60 days, as outlined in the Micronutrient Application Guide.

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Re: CDC 2787 Soil Test

Post by cdc2787 » April 20th, 2021, 4:56 pm

Andy and Morpheus, thank you for your interpretations. I will be tackling the Iron and Boron shortages this season. I ordered Ferrous Sulfate powder from 7springsfarms.com and will see how it goes in the spreader alone. Based on the picture from their website it doesn't appear to be a fine powder. If that doesn't work out, can I combine the Ferrous Sulfate with the Twenty Mule Team and Milo application? Will this cause any negative reactions?

For future reference, if I go with the moss killer option for Ferrous Sulfate, I would have to use the formula mentioned above to determine how much moss killer must be applied to reach 2-3 lbs/K of Ferrous Sulfate, right?

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Re: CDC 2787 Soil Test

Post by MorpheusPA » April 20th, 2021, 5:28 pm

More or less. This is not an exact science, and for surface-applied ferrous sulfate, I'm far less concerned about blackening grass. It's much less likely to happen as the roots are far more picky about absorption than leaves are. Sprayed leaves on bluegrasses can turn a very dark blue-green.

Sprayed leaves on fescues can turn this really funky battleship blue-gray that lasts for up to six months. The plant is fine, perfectly healthy, and grows normally. It just looks...alien. K-31 seems particularly susceptible.

Extreme levels can damage or kill a plant when sprayed. Except at low pH, that's extremely unlikely with soil application and you'd have to pour it on at rates that you couldn't manage or afford.

I'd just go at bag rate, personally. And then, in the future, feed with Milorganite. It has the same amount of iron, but the rest of it is lawn food--for about the same price. You can substitute it for your May, September, and October feedings in Berks/Bucks county (and up here in Northampton, as I do, except with other stuff).

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Re: CDC 2787 Soil Test

Post by andy10917 » April 20th, 2021, 5:47 pm

Go with the bag rate. And surface-applied Ferrous Sulfate *CAN* blacken the lawn if overapplied. I know that the Scott's Moss Killer product (Iron Sulfate and filler) had a warning about that very symptom the last time I read the bag (a couple of years ago, IIRC).

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Re: CDC 2787 Soil Test

Post by MorpheusPA » April 20th, 2021, 6:04 pm

"less likely" not "impossible" :-) It's hard to kill them with soil-apped iron, but you can certainly blacken them. My English can sometimes be a little opaque.

I did once overapp on a mixed lawn at 6 oz/K spray iron. I couldn't manage it on elite bluegrass with twice that, but...elite bluegrass. Taking a glance, Scott's is about 6% iron, 19 lbs, covers 5K square feet, so call it 4 lbs/K, or 0.25 pounds iron per K, to shoot high throughout. Or about 4 ounces ferrous sulfate per thousand, surface applied.

At pH 6.6, that doesn't concern me at all; it's at the higher end. Bag rate is fine. (Cough) Personally, I'd probably go higher as it's surface-applied and won't foliar absorb uncontrollably, but won't specify how much higher I'd actually go just to give plenty of margin for error. (Cough)

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Re: CDC 2787 Soil Test

Post by cdc2787 » April 21st, 2021, 9:15 am

Maybe I'm being a little dense here, isn't there a large difference between the recommended Ferrous Sulfate application of 2-3 lbs/K and Scott's moss killer bag rate containing only 4 oz/K of Ferrous Sulfate?

I have an 18,000 sq ft lawn and was ready to apply 36 lbs total (2 lbs/K) of the Ferrous Sulfate powder. If I were to use Scott's moss killer at bag rate, using Morpheus' numbers above, I would only be applying 4.5 lbs total of Ferrous Sulfate.

Would using bag rate of the moss killer just take more applications to amend my soil? I'm just trying to figure out which is more cost effective as well as any pros and cons. I apologize for having so many questions, but I misunderstood this recommendation in my last interpretation and don't want that to happen again.

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Re: CDC 2787 Soil Test

Post by MorpheusPA » April 21st, 2021, 2:31 pm

No, you're of duly low density. Iron's an element that's only used at low levels at any one time, and applying it at higher levels wouldn't be good for the soil or the lawn. So we put it down a little at a time, over a period of time, to let things adjust to it.

If you were to use way too much, it could be toxic (that would be very tough though, and you'd just turn the grass funky colors long before that; you'd actually have to shift the soil pH with what you're using and...well, that's just not going to happen easily across an entire lawn).

So this isn't a once-and-done process, it's something you'll do every now and again over the course of years. Or use Milorganite to feed your lawn (it has about the same level of iron) and let that do the job over time while it also does the feeding job as well. Iron's not something that builds up and destroys the soil very easily (there are places with names like Red Clay which usually aren't clay, but are red, where iron levels are 50,000 PPM and plants grow just fine).

If you applied Moss Out monthly, that would be fine. Expensive, but fine. If you simply fed with Milorganite on Memorial Day, Labor Day, and October first, that would add...about 2/3 pound, or 10-11 ounces elemental iron per thousand square feet (in a different complex form than ferrous sulfate so the same warnings don't apply) with each application if you feed at bag rate. Personally, I tend to recommend exceeding bag rate in fall by about 1.2x-1.5x. With a lawn your size, you may not want to do that; I do on 10K square feet.

Your third option here is to simply purchase a large bag of ferrous sulfate and a hand-held whirlygig spreader. Apply that at about 1/2 pound per thousand square feet (the lowest those spreaders can go, although if you look, you might find one that can successfully go lower) on a windstill day before rain. Repeat twice per season. The best bang for the buck is probably going to be ferrous sulfate monohydrate (white crystalline form, 15.4% iron by mass) in this case but ferrous sulfate heptahydrate (teal or green) might beat it in terms of price due to being more extensively made, even if less iron by mass (10.6% iron).

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Re: CDC 2787 Soil Test

Post by cdc2787 » April 22nd, 2021, 4:21 pm

Thank you for all your help and answering my questions.

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