Pawpaw Potassium Deficiency?

General Fruit Growing
#1

Today i noticed a few of my pawpaw trees are showing some very clear issues.
This it the third year of my orchard but first time i’m seeing this.
Also, the symptoms only began appearing a few weeks ago.

These pictures are showing older leaves - younger leaves look totally fine.

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I consulted the frequently used document for diagnosing pawpaw nutrient issues, and none of the pictures really look like this; however, the verbal description of potassium deficiency is pretty close (older leaves, yellow margins)

Also, the very well-respected Spectrum Analytic website says this about K deficiency:

The classic and almost universal leaf deficiency symptom is marginal chlorosis of the older plant leaves.

Spectrum goes on to say:

It might also show as a fruit crop that doesn’t quite develop the proper quality or flavor.

While this is a really small sample size, my one pawpaw fruit this year fit this description exactly.

Also searching here, i saw mention of K deficiency causing persimmon fruit drop. My pawpaw dropped i believe prematurely, which also fits.

Thoughts?

Now then, to save time let’s assume this is potassium deficiency.
How should it be corrected?

I had the orchard tested this spring with these main results:
pH 6.8
Phosphorous 519 pounds/acre
Potassium 194 (listed as “high”)
Calcium 9806
Magnesium 393
(these are Mehlich-1 values)

I have known for a while that i need to get my pH down. It actually started 3 years ago at about 7.5 and thru elemental sulfur and compost, it’s come down. I want to get it down even more, to 6 would be wonderful. I’m not sure getting it to 6 will make this issue go away because…

… I have apparently 50x higher Calcium content compared to K. Spectrum Analytics mentions Calcium competes with K. That’s an awful lot of Calcium.

So I guess I don’t know if adding K to the soil will really do anything. I could try foliar feeding, but that’s a hassle.

Part of me is freaking out thinking that I am doomed to have crappy, premature-dropping, gross pawpaws forever :sob:

Help!

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#2

Did somebody farm there before and add a bunch of lime?
There was a similar question online and here is someone’s answer:

I have a case at a field at a Norwegian farm which has excessive calcium levels. How can this be reduced in the best way? I´m looking for a procedure.

Some data on the field:

  • Total exchange capacity (TEC) is 7,32 (silty sand)

  • Active pH is 7,9

  • Calcium saturation is 95,4 % - desired 66 %

  • Magnesium saturation is 1,4 % - desired 14 %

  • Potassium saturation is 1,1 % - desired 5,3 %

  • Sodium saturation is 0,4 % - desired 0,9 %

  • Among the micronutrients boron and manganese are low.

  • The soil structure is collapsed (over-flocculated)

The reason for this extreme calcium saturation is that the field had calcium stabilized sewage sludge applied some 17 years ago. Since then almost nothing has grown there. The farmer, and we, are looking for solutions. It is an organic farm.

My own first suggestion is the apply elemental sulphur (S) in high doses (to acidify and leach out Ca as CaSO4) and , i.e. 100 kg/ha plus kieserite and potassium sulphate (200 kg/ha of each).

The case is in farm and suggest to plant some leafy root crops which have high oxalate level and immediately the high calcium level in the soil will react with the oxalic groups in the crops and become soluble nature. so this will be good mechanism.

The guy mentioned it was an organic farm,so that’s the kind of answer he received.
From what I’ve read,Pawpaws like 5.5 to 7 pH,so yes,that can go down.I’d suggest something like Sulfur or acid to reduce the Calcium.bb

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#3

Thanks for the info.
I don’t think the area has been farmed and therefore limed in the past. I think the issue is that I’m on the slope of a “mountain” (really just a good-sized hill). There are limestone outcroppings in a few places on my property…the soil is only a couple feet on average above solid limestone bedrock. I assume that’s why my Ca is so high.

Yes i definitely need to add more sulfur. Just not sure if adding K will help or just be a waste.
Of course, this assumes that the issue is K deficiency, which is yet to be established…

I did some irrigation with sulfuric acid diluted to pH 5…but that is time-intensive, requires a drier soil condition (i.e. plants need the water) and i wonder about the long term efficacy.

#4

When i Google images of leaves with K deficiency, I realize that I have been seeing this for years with other things i’m growing and I never realized it.

Primarily my maypops…textbook K deficiency signs. I think even my muscadines have shown some of this in the past.

I never acted on the maypop issue because the plants still were very productive and seemed to be inconsequential.

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#5

Try some wood ashes from a camp fire or stove…takes care of potassium deficiency.
(And raises pH)

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#6

Calcium and potassium work together so i would think you do need some potassium and that its probably a deficiency in k as a after effect of the heat. However i think epsom salts is what you need to add also.

You can foliar the k and epsom salts to get it to them now if you want.

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#7

Thanks Bb! I think I will hold off on this since I need to lower my pH.

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#8

Thanks! I have had others mention Mg too, but my soil level is fine (as is K) and I believe I read Mg competes with K. If that’s true, adding Mg could make it worse.

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#9

The leaves show more magnesium deficiency rather than K and you get k deficiency (as well as others) with high heat. While k and mg are not super compatible with each other they are not bad when you add in sulfur and work together in a foliar spray which is probably the only way to get that issue fixed now.

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#10

Thanks!
At this point I’m kind of looking for the smoking gun, an explanation of why this is happening as much as WHAT is happening.
The soil test seems to show sufficient quantities of all major nutrients and a not-crazy pH. So what would cause this?

You mentioned heat, and I guess moisture conditions can have an effect.
So am I just looking at temporary, transient conditions that I can’t necessarily control, and therefore should worry too much about?

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#11

Nutrient lockout, probably from calcium. Using sulfur to reduce the pH to ~6.0 might help.
https://www.advancednutrients.com/articles/nutrient-lockout-prevent-diagnose/#:~:text=Nutrient%20lockout%20occurs%20when%20plants,media%20and%20your%20plants%20themselves.

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#12

I am fairly ignorant of soil chemistry but that’s what I was thinking had to be going on. Some kind of antagonism …

#13

Now i’m circling around to thinking it’s more of a magnesium issue versus potassium.
I plan to send some leaves off for analysis and also experiment with foliar feeding.

#14

Wondered if you ever figured out what deficiency this is ?
I Have similar symptoms on a few potted Pawpaw

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#15

Yep - I sent leaves off for tissue analysis and compared to baseline values from KSU which confirmed Magnesium deficiency.
I recently posted a video about it too:

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#16

The only way you are getting that is with a soil analysts, everything else is conjecture.

Heck a foliar application of Epson salts would provably green them up in record time, both the magnesium and sulfur will do wonders for chlorophyll, but that may just mask your real issue; out of whack soil acidity that is interfering with uptake.

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#17

Hey Don!
Yes since that post I’ve definitively determined the issue and 2 causes - high Ca and localized low pH, the latter caused by yours truly :man_facepalming:
You may not have time to watch the video above, but I explain it all there.

#18

Found this …
Says foliage application does not go back into the rest of plant …
Oops this is about manganese , not magnesium !

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#19

That document is dealing with Manganese versus Magnesium.
Magnesium is highly mobile within the plant.

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#20

Oops , my bad

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