[VerdantGreen]

Citric acid is something i have used for a while to lower the pH of my tapwater to a more friendly level. it starts off about 9 and i like to bring it down to about 6. im sure you've all heard me banging on about it
But the more i use it and find out about it, the more i am convinced it has many positive benefits for my plants, and the more interesting it gets as to the role that citric acid plays as a root exudate and in making nutrients - largely P - available.
because citric acid tend to get talked about as a secondary subject in other threads, ive been meaning to start a thread and attempt to gather some useful posts from the four winds into one place. anyone else with experience or knowledge please contribute.



here are posts by spur that has some good references

Another very useful additive is citric acid. The reason citric acid is a great additive is it bonds to P anions keeping them soluble in the rhizosphere and soil solution. Also citric acid helps the Krebs cycle. The reason P anions are not needed by plants at the same level of N, K or Ca is that P anions are not readily available to plants in nature, thus they have evolved to use lower levels of P than other major elements. I could explain all the why's but this post would get long and IME most people don't care about the why's as it gets technical in the topic of soil science.

In short, P anions are not very mobile in the soil solution (thin layer of water surrounding particles in media, soilless and soil) and are readily bound and made insoluble to media particles and other elements and organic substances; critic acid prevents this. The soil solution holds cations in equilibrium to the cations held in cation exchange sites of media particles. Roots exude large amounts of citric acid that keeps P anions soluble in rhizosphere and soil solution. Roots also 'feed themselves' by exuding critic acid (and other acidic chemicals/substances) that mineralizes P anions from organic matter like soft rock phosphate, etc.

Originally Posted by spurr

@ VG:

Here is some info about citric acid, and other ornic acids exudates by roots and microbes that solublize organic matter. For info on citric acid see the references below, esp. the first few, hope this is helpful. (thanks MM for the email)
----------------------------------

I hope I didn't come across as claiming their are saprotrophic plants; AFAIK there is no such thing, plants that where termed saprophytes** are really parasitic upon mycorrhizal fungi. Plants that were termed saprophytes are now termed "myco-heterotrophs" (see references below). I was referring to normal plants the can break down organic matter essentially feeding themselves, not myco-heterotrophs like non-photosynthetic orchards. Dicots tend to emit more organic acids than other monocots, esp. leugems, to my understanding.

** The term saprotrophic or saprophyte is now detritivores or saprophage. So saprophyte fungi are now called saprophage fungi.

I believe P is a major element that is freed (solubized via mineralization) from organic matter when roots emit or create weak acids in the rhizosphere and soil solution. Other elements like Ca, Fe, and I think N, etc, can be solublized too. The amount of ions the plant solublizes via acids isn't high, but can make a difference for P anion which has poor soil solution mobility and often gets tied up.

I'm sure you know most of this already, so please ignore any info that seems to assume you don't know something (like info about the soil solution).

Below I use "solublize" and "solublization" interchangeably with "mineralization"; to mean ions are freed from organic matter.


Here are some acids emitted or made by roots:

- Carboxylic acid: emitted by roots, lowers rhizosphere pH which effects ion availability (esp. P) and also solublizes some organic matter releasing ions the plant cant take up (ex. soft rock phosphate especially when the bulk soil pH is weakly acidic like 6 to < 7).

- Carbonic acid: similar to carboxylic acid but carboinic acid dissociates back into Co2 and water in the presence of water. Carbonic acid is formed when the roots emit Co2 and the Co2 mixes with water. Carbonic acids are pretty stable, however, in the presence of water it can dissociate into Co2 and water. Carbonic acid are similar to carboxylic acid in terms of rhizsphpere pH, and pH of soil solution and mineralization of some types of organic matter. Carbonic acid can be dissociated into Co2 and water via. exudates by bacteria (i.e. "carbonic anhydrase") that prefer neutral to basic pH levels.

- H+ protons: emitted by roots when roots take up ammonicial nitrogen such as ammonium (NH4+). This is why ammonium is said to be acidic, because of the reaction by the roots after taking in the cation. When H+ protons are emitted by roots it lowers rhizosphere pH and also can solublize some organic matter freeing ions the roots can use. When roots absorb nitrate N they emit bicarbontes, which are basic, and is why nitrate is said to be a basic (alkaline) form of nitrogen (roots also emit anions when nitrate is absorbed).

- Citrate (ex. citric acid): emitted by roots and lowers rhizosphere pH and can solubilize some organic matter. One of the acidic exudates with the highest level release by roots

- Oxalate: can provide nearly the same level of mineralization of soil P (from organic matter) as citrates. Oxalate is an acidic exudate of some mycorrhizal fungi (ex. AM fungi) used to solublize soil P.

The acids listed above is not a complete list, just an example. By the process of mineralization of organic matter the exudates (ex. citric acid) releases ions into rhizosphere and the soil solution (thin film of water surrounding media particles; where microbes and ions can be found). The roots can then use the ions in the soil solution or rhizosphere depending upon the pH of the liquid and solubility of the ions. The soil solution has an equilibrium of cations to those held by media cation exchange sites. Citrate has a large affect upon P anion in terms of increasing their bio-availability to roots, this is in regards to solubility of P anions already in the soil solution and/or rhizosphere.

Below are only a couple of quick references I have handy, I will put together other references for you. I think the weak acids I listed above are the same weak acids the Luebkes (e.g. Controlled Microbial Composting) refer to in terms of roots exudates that can solublize some organic matter.

Here is a good quote from the paper: Bioavailability of soil inorganic P in the rhizosphere as affected by root-induced chemical changes: a review
References:

1. Bioavailability of soil inorganic P in the rhizosphere as affected by root-induced chemical changes: a review
Philippe Hinsinger
Plant and Soil 237: 173–195, 2001.
(full text) https://www.plantstress.com/Articles/...ailability.pdf


2. Effects of root exudates on nutrient availability in the rhizosphere
A. Gransee
Plant Nutrition Developments in Plant and Soil Sciences, 2002, Volume 92, Symposium 9, 626-627,
(abstract only for now) https://www.springerlink.com/content/n216w5006k27754p/


3. The release of root exudates as affected by the plant physiological status
R. Pinton, Z.Varanini, Z. Nannipieri (eds.)
The Rhizosphere: Biochemistry and organic substances at the soil-plant interface. Marcel Dekker 2000.
(full text)
https://www-mykopat.slu.se/Newwebsite...nRoemheld2.pdf


4. Root exudates as mediators of mineral acquisition in low-nutrient environments
Felix D. Dakora1,3 & Donald A. Phillips
Plant and Soil 245: 35–47, 2002
(full text) https://www.fsl.orst.edu/~bond/fs561/references/Dakora%20and%20Phillips%202002 %20Root%20exudates.pdf


5. Carbonic Acid Decomposition
Richard E. Barrans Jr., Ph.D.
Assistant Director
PG Research Foundation, Darien, Illinois
(full text) https://www.newton.dep.anl.gov/askasc.../chem99661.htm


6. "Ecosystem Physiology: The Plant-Microbe Dance"
(I do not agree with everything written in this reference, but the info about carbonic acid is sound)
by Leslie H. Kirkegarrd
(full text) https://grow-orchid-grow.com/science_...obe_Dance.html


7. "A Touch of Chemistry"
https://www.treedictionary.com/DICT2003/shigo/CHEM.html


8. "Troubles in the Rhizosphere"
https://www.treedictionary.com/DICT2003/shigo/RHIZO.html


9. Plants parasitic on fungi: unearthing the fungi in myco-heterotrophs and debunking the ‘saprophytic’ plant myth
JONATHAN R. LEAKE
Mycologist, Volume 19, Part 3 August 2005.
(full text) https://www-mykopat.slu.se/Groningen/Leake.pdf


10. Myco-Heterotrophs: Hacking the Mycorrhizal Network
Peter Werner
Mycena News, March 2006
(fell text) https://www.mykoweb.com/articles/Myco-Heterotrophs.html

[VerdantGreen]

another post

Originally Posted by spurr

Sounds good, it would get lost here you're right. FWIW, I use citric acid I buy from a wine and beer brewing shop to drop water pH from 6.00 to 6.10. Dropping pH to that range allows me to add a decent amount of critic acid which is my goal.

I don't use citric acid to drop pH but it's a side effect of using it to increase the Krebs cycle, organic matter mineralization and P anion solubility in rhizosphere and soil solution. As has been discussed elsewhere, for organics a water pH from 5.5 to 7.5 is fine, even up to 8 is OK, and water pH has very, very little effect upon pH of media (rhizosphere and soil solution). The alkalinity of water is what has much greater effect upon pH of the media than the pH of water; and roots/microbes have a great effect upon pH of rhizosphere and soil solution.

Water with high alkalinity has pH over 7 but water with pH over 7 doesn't necessarily mean high alkalinity.

In hydro with chems water pH is much more of a concern, as well as alkalinity and level of ammonicial N (ex. ammonium, which makes roots release acidic H+ protons lowering pH) and nitrate (which makes roots release basic bicarbonates increasing pH).

On the topic of ammonicial N, that is one reason why fungal rich media has lower pH. Because fungal rich media often has greater pools of ammonicial N than does bacterial rich media; thus when roots take in the ammonicial N (mostly as ammonium, NH4+) they release acidic H+ protons. Bacterial rich media often has greater pools of nitrates (NO3-); thus when roots take in the nitrate N they release basic bicarbonates increasing pH.

P.S. I have other papers on the topic of critic acid I can post in your thread you will start.

i get my citric acid powder from ebay - it's used in soapmaking, preserving etc. i mix up a bottle of solution using about a tablespoon in a pint of water and then use 2 or 3 tablespoons of this solution in a couple of gallons of water. this is enough to bring the pH of my water down to about 6

[VerdantGreen]

more

Originally Posted by spurr

@ VG,

Below is a good article from Greenhouse Grower about P and plant growth. It covers what I wrote about in more detail, such as Fe making soluble P anions insoluble (not bio-available to plant roots) and low movement of insoluble P anions within soil solution.

I think you read my other thread I wrote elsewhere ("Tissue nutrient analysis of Cannabis = rethinking Lucas and N-P-K-Mg-Ca-S") providing lots of cannabis tissue analysis and references about why lower levels of P is good for cannabis. And that the very high levels of P given to cannabis is silly and not helpful. This article covers these topics well. For my ongoing tests using chem ferts with compost teas and microbial rich inputs (using a microscope to see the effects upon microbes) I keep P level below 50 ppm all the time, but most cannabis ferts, ex. Lucas formula, provides P over 100 ppm!

High P means greater plant stretch (internodal length) and less root growth (root to shoot ratio), along with other potential problems. This is why boosting P during pre-flowering isn't wise IMO.

In the quote below the author discusses what happens to P anions in rhizosphere and soil solution, however, we as cannabis growers tend to provide much more Fe than greenhouse growers not growing cannabis. Thus Fe has greater impact upon making soluble P anions insoluble. As well as the effects of media particles making P anions insoluble (binding to them, but not in terms of anion exchange capacity). This is why I think adding citric acid is wise because it prevents/reduces Fe and media particles from making P anions insoluble.


"An Eye On Phosoporus Nutrition: Understanding how phosphorus acts in soil and in the plant will help you regulate vegetable transplant growth."
By Shiv Reddy; September 2010

https://www.greenhousegrower.com/magazine/?storyid=3753

For anyone who wants to read the thread I wrote "Tissue nutrient analysis of Cannabis = rethinking Lucas and N-P-K-Mg-Ca-S" I uploaded here: (link) and the password to decrypt the file is "references" (without quotes). The file host is in Russia and doesn't require Javascript, etc., thus it's more anonymous IP wise than a U.S.file host.

[VerdantGreen]

some background reading on the krebs/citric acid cycle - im sure spurr will approve of the wiki link

https://en.wikipedia.org/wiki/Citric_acid_cycle

Hello VerdantGreen.. I've read that citric acid, I didn't know they made a powder version, when used for Phing, doesnt last very long and Ph will rise relativly quickly after application.. and, the liquid version, in DWC, can cause pump failures and clogged stones (what doesnt clog air stones??)... it is sticky..

I've never used it but these are the reasons why.
I have thought about using it to lower my overall body Ph..

[VerdantGreen]

hey scrog from what i understand, it is the alkalinity of your water supply that will determine whether the citric acid has a long or short term effect on your water pH, but as i mentioned the positive effects of citric acid are much more than just pH (and pH is not as relevant in organics anyway, my water source is high pH High alkalinity so i amend it)
not sure about pumps and airstones im afraid.

carl carlson has a good thread about alkalinity and pH - ill try and get a link

VG

[VerdantGreen]

here is a link to carl's thread on water pH and alkalinity and how it effects soil grows.

https://www.icmag.com/ic/showthread.php?t=169662

[VerdantGreen]

couple of links that i found a while back - just extracts - may have limited relevance

https://www.nature.com/nbt/journal/v1...t0400_450.html

https://www.springerlink.com/content/f22x4773860r6031/

VG

[VerdantGreen]

as you can see from the links, citric acid is useful for making the P in soft rock phosphate available.

i'd be interested in the dosage of SRP that others use and whether it is their primary P source.
i didnt really know how much when i first got it - so started at 5g per litre of soil - which is the same as 1 tablespoon per gallon. ive stuck at this because the plants seem happy (although i also use high P bat guano too - i regard SRP as a secondary P source in my mix).

question - will citric acid have the same effect on the P in my guano, making it/keeping it available?

VG

[spurr]

Hey VG,

I will post some info in this thread later today, I have to head out now, but I wanted to post the following study...

This paper shows how plants can self-limit P uptake to try and prevent toxicity, and described how in P sufficient soils and P deficient soils (where P is applied) up to 80% of soluble P anions are made immobile (insoluble) by Fe, Al, high pH, microbes, etc. This is one reason why cannabis and other plants have developed less need for P due to lower P bio-availability in soil as plants were evolving. This paper ties into in the article from Greenhouse Grower about phosphorous I posted in one of my quotes above.

This paper also talks a lot about mycorrhiza between host plant root and AM fungi; how it increases in P uptake by roots we all know about.

Update on Phosphorus Uptake: Phosphorus Uptake by Plants: From Soil to Cell
by Daniel P. Schachtman, Robert J. Reid, and S.M. Ayling
Plant Physiol. (1998) 116: 447-453
https://www.plantphysiol.org/cgi/reprint/116/2/447 (full PDF)