Coconut nutrient deficiency of my own making :Þ Suggestions?

[KarenRei]

Apart from the occasional problem with spider mites, my coconut has always been nice and healthy.  But I got a pH meter for Christmas (it's been way too long since I've had a working one) and I've been thinking more and more about optimizing my soil pH individually for each of my plants.  Most (but not all) plants were measuring above-optimal pH, and among them the coconut, so I added some ammonium sulfate (along with other macronutrients to balance it) to lower the pH. 

Mistake.

1) I don't think this pH meter is reliable. At all. It's not a professional one.

2) The pHs were likely changed too much, too quickly. 

I had one Passiflora edulis die (although honestly, good riddance - I have too many and they're taking over!) and one Inca nut die (not "good riddance"  :Þ)  Most plants indicated no harm, but a couple showed what seems to be some adverse consequences.  And among them my Fiji dwarf coconut.

Sorry for the picture quality; my grow area is LED lit and I had to shut the lights off so that everthing isn't washed out by pink:

You'll first off notice some leaf blades missing.  Those were yellow when I last checked did a leaf inspection several days ago.  I trimmed off all that was yellow, so that any new colour changes would be easily visible.  So all that's yellow now has come since them.  I believe this is magnesium deficiency, given the pattern of how it's been going yellow. Potassium deficiency is similar, but the tips and edges brown, and that hasn't been happening - indeed, the tips are actually still green on a lot of these (here's me holding one blade by the tip)

Magnesium deficiency can be caused by too acidic soil, which would also make sense.

During the last inspection / clipping, I decided to try to undo part of my "handiwork"; I mixed a pinch of cement into a watering can and watered with it.  Cement = calcium oxide = forms calcium hydroxide = lime.  But - having overadjusted once - I didn't want to risk overadjusting in the other direction.  I haven't seen any change to the yellowing.  I could keep doing so if it would be advisable.  I also have some pelleted lime, although it'll be slower acting.

I also have worries about adding "additives" too frequently if only for the fact that it also involves adding water.  I know coconut roots can rot if you overwater them.  Nutrient deficiencies are bad, but root rot would mean a dead tree  :(.

What are your thoughts on what I should do?  This evening, for the first time, I tried making a homemade foliar spray ; I dissolved some general-purpose fertilizer, and added some extra magnesium, and sprayed it on dilute.  I don't know if it'll help any, but it seems a reasonable thing to do, no?

All advice welcome!

Edited March 1, 2018 by KarenRei

[KarenRei]

I suppose another possibility is nitrogen deficiency. Is it even possible that adding ammonium sulfate could cause a nitrogen deficiency, given that its a nitrogen source?

[KarenRei]

Alternative hypothesis: it could also be that this is something that had been brewing for a while, and the fertilizer had no effect, but I only just now noticed it because I'm paying more attention.  There's an older leaf that also has some yellow, and dead parts, but it's blotchier and I honestly think it's just old spider mite damage.

I don't think this hypothesis is correct, but it's worth consideration.

I figure I should also add a better description of the leaf yellowing.  It's "inside out"; tips, edges, and bases are the last parts of the leaf blades to yellow.  The primary vein in each leaf blade doesn't stay very green, but it stays a little greener than the rest of the leaf, and some of the secondary veins seem to be a bit greener than the rest.  But it's never a prominent, stark green contrast to the yellow.  The leaf that I photoed, the one that's prominently yellowing, is an older leaf.

Edited March 1, 2018 by KarenRei

[GottmitAlex]

A "pinch of cement" wont do anything to it. It is probably a "precondition".  I know cement wont do it because 5 months ago in my patio they were working on a cinder block wall and when they finished with it, the handyman's assistant gathered the residual cement puddle (a considerable amount ) and swept it into one of my coconuts' plot. The Jamaican/Atlantic tall.  I was not at home at the time... 

But to make a long story short. The Jamaican tall coconut did not show signs of any damage. Just kept on growing...

 

 

[KarenRei]

".  I know cement wont do it because 5 months ago in my patio they were working on a cinder block wall and when they finished with it, the handyman's assistant gathered the residual cement puddle (a considerable amount ) "

Are you talking hardened cement or liquid?  It's much more available as a liquid.  But lime (calcium hydroxide, what you get from hydrated cement) *absolutely does* raise soil pH; lime is specifically sold for the purpose of raising soil pH (go to any garden supply store).  And even hardened cement will raise soil pH over time - just slower.

https://www.ncbi.nlm.nih.gov/pubmed/16981250

"Soil adjacent to new brick veneer work is likely to have a higher pH owing to the mixture of cement with the soil. In the Gainesville, FL, area, soil samples taken from such locations had a range of pH values from 9.0 to 10.1; similar soils used in bioassays had a pH of 5.6 before the addition of cement. Addition of 15 mg of Portland cement to 33 g of soil increased the pH to 6, and addition of 291 mg of Portland cement increased the pH to 9."

And the suspected problem is overly acid soil, not overly basic.

In the above link, the former figure, used to raise from 5,6 to 6, equates to a 0,045% mixture of cement with soil.  Let's see... give the size of the pot (probably 300-400l)... it should that would be about 150 grams.  More than a pinch certainly, but not a huge amount.  Then again, I didn't add all *that* much ammonium sulfate - maybe 5 tablespoons?  But then again, we're probably not talking the whole depth of the pot, I wouldn't be surprised if the upper layers are much more affected than the bottom layers.

Anyway, as mentioned, I wanted to err on the side of caution on remediation, to avoid risking making a problem worse.  Should I keep working to raise soil pH while foliar feeding, or...?  How insistant should I be on giving the soil time to dry vs. "rushing" remediation through?  Again, my big concern is, "when you're in a hole, stop digging".  I don't want the cure to be worse than the disease.

(Ed: there's some leaf litter on the surface of the soil from other plants. I should probably remove some of it to help the soil dry faster)

Edited March 1, 2018 by KarenRei

[KarenRei]

Ah, and here you go, this is why you don't rush into trying to remedy a problem: many papers are noting that there's heavy competition between NH3+, K+, Na+, Ca+2 and Mg+2. That is to say, rushing to lower the pH by adding a bunch of bases (horiticultural lime (or cement), KOH, etc) can actually make the problem worse, not better. Calcium in particular.  And sometimes it's one-way, with magnesium always the loser - for example, high K+ hinders Mg+2, but high Mg+2 does not tend to hinder K+.  But Mg+2/Ca+2 competition appears to go both ways (normally to the detriment of Mg+2)

Apparently Mg deficiency (again, assuming my reading of the symptoms is correct) is common.  NPK fertilizers can even promote it.  Mg is highly mobile in soils and plants, and can be prone to leaching. 

What to do?  In addition to when it's low in general, when its absorption is artificially being hindered by cation competition: "In such soils improvement and maintenance of a balanced nutrient supply to crops is extraordinary important. The fixing sites need to be filled up with Mg through a fertilization strategy which provides Mg in amounts much higher than extracted with the crop."  Sounds like I shouldn't be worried about the pH so much as just simply the raw Mg levels.

High light, drought, and heat stress increase magnesium needs.  The former is not an issue for me, and I probably am much more at risk for excessive moisture than drought.  But heat stress could be real. I'll open the tent a bit more.

More nitrogen shouldn't be needed at present, due to recent fertilization. But in the future I should stick to nitrates; rather that competing with Mg for uptake, they promote it (although they do reduce the rate of translocation within the plant).

Edited March 1, 2018 by KarenRei

[KarenRei]

Are you in agreement that it's magnesium deficiency, from the description and the (admittedly limited) pictures?  Or should I go clip a leaf blade to get better pictures?  I don't want to end up treating the wrong condition 

Edited March 1, 2018 by KarenRei

[GottmitAlex]

11 hours ago, KarenRei said:

".  I know cement wont do it because 5 months ago in my patio they were working on a cinder block wall and when they finished with it, the handyman's assistant gathered the residual cement puddle (a considerable amount ) "

Are you talking hardened cement or liquid?  It's much more available as a liquid.  But lime (calcium hydroxide, what you get from hydrated cement) *absolutely does* raise soil pH; lime is specifically sold for the purpose of raising soil pH (go to any garden supply store).  And even hardened cement will raise soil pH over time - just slower.

 

Very much like this. About 3 gallons worth...

The person who did this our handyman's new son-in-law. Needless to say, since this incident, my handyman works alone.

His son-in-law was upfront with him and told him what happened. 

 

 

Edited March 1, 2018 by GottmitAlex

[KarenRei]

Geez... with that sort of quantity I'd be more worried about starving the roots of oxygen than pH!  ;)

[GottmitAlex]

Yeah, I'm grateful I did the plots in 3x3x3ft of pure sand. 

[Jamesasb]

On 01/03/2018, 01:35:25, KarenRei said:

I suppose another possibility is nitrogen deficiency. Is it even possible that adding ammonium sulfate could cause a nitrogen deficiency, given that its a nitrogen source?

depends because ammonium isnt so helpful it takes time for microbes in soil to turn it into nitrate.  i think a big hit of ammonium could cause problems in the short term

[Bennz]

KarenRei, this is a really interesting question. Unfortunately I think you need to have a soil and foliar tests set before us before anyone could answer even semi-usefully, and even then we would need to know what mineral levels coconuts actually prefer, eg, do they prefer coastal salinity or merely tolerate it? Is the palm potted, or in the ground? If in a pot, I find some trees just plain do not like organic potting media, and are much better grown in pots with pure mineral soil. Acacia elata is a prime example, and I'm starting to think mango might be another (needs more work to prove this!). Some trees love to grow in pumice, others (eg Acacia dealbata) die at germination in pumice. I don't know enough about coconuts to be any help at all.

 

If that tree was growing in the ground at my place, and knowing my soil mineral status, I would immediately assume it was Sulphur deficiency, not magnesium. Your soils are probably totally different. Fun speculating though.