Cation Exchange Capacity in Coco

[YosemiteSam]

OK, I have a basic understanding of what CEC is but I definitely do not understand the finer points. I get that the coco fibers themselves will attract some of the cations out of the nutrient solution and that the fiber particularly likes Ca+2 and to a lesser extent Mg and K.

So I understand that when you first start feeding that the coco sort of competes with the plant for the cations you feed. But at some point those fibers will have all of the cations they can hold (it is called a high cation exchange capacity medium, not an infinite cec....correct???).

Here is where my understanding starts to lack. Once that cec is satisfied what happens next? My limited chemistry background tells me that once ionic bonds are made they are fairly tough to tear apart. So once that cec is satisfied does the coco become effectively inert...merely letting all of the water and nutes from that point on either go to the plant or pass on through? Or, as some seem to imply on this site, does the fiber go right on exchanging cations, trading one for another as the nutrient solution passes through?

If anyone has a deep understanding of this I would appreciate hearing your thoughts.

 

[Oregonic]

good question. i look forward to the experts chiming in...

 

[*mistress*]

cation exchange capacity

cation exchange capacity

Cation Exchange Capacity in Coco
OK, I have a basic understanding of what CEC is but I definitely do not understand the finer points. I get that the coco fibers themselves will attract some of the cations out of the nutrient solution and that the fiber particularly likes Ca+2 and to a lesser extent Mg and K.

So I understand that when you first start feeding that the coco sort of competes with the plant for the cations you feed. But at some point those fibers will have all of the cations they can hold (it is called a high cation exchange capacity medium, not an infinite cec....correct???).

Here is where my understanding starts to lack. Once that cec is satisfied what happens next? My limited chemistry background tells me that once ionic bonds are made they are fairly tough to tear apart. So once that cec is satisfied does the coco become effectively inert...merely letting all of the water and nutes from that point on either go to the plant or pass on through? Or, as some seem to imply on this site, does the fiber go right on exchanging cations, trading one for another as the nutrient solution passes through?

If anyone has a deep understanding of this I would appreciate hearing your thoughts.

cation exchange capacity
ability of media/+nutrient solution to hold positive charges (cations) available for uptake by roots.

cec measurements:
milli-equivalents=the # of charges a cup of media can hold. standard measurement is 100g of media by weight, or 100cc by volume. vermic., perlite, etc. measured by weight instead of volume.

cec 0=media hold no cations available for roots.
cec 100=media holds cations for roots under all conditions.
examples:
peat moss-90 (similar to coco)
vermiculite-20
perlite-0

cations
repel like charges/positively charged ions
hydrogen (h+)
potassium (k+)
calcium (ca++)
magnesium (mg++)
ammonium (nh4+)
iron (fe++)
manganese (mn++)
zinc (zn++)

absorbed mostly on negatively charged surfaces.

anions
attract like charges-negatively charged
nitrates (n03-)
phosphates (hp04--)
sulphates (s04--)
chlorides (cl-)

nutrient example: potassium nitrate. metal cation (k+) bonded to non-metal anion (no3-)=kn03.

almost exclusively in nutrient solution. easily leached away.

plants 'exchange' ions for ions during uptake. for every 1 potassium (k+) or ammonium (nh4+) ion absorbed, 1 hydrogen (h+) ion is released into media+nutrient solution. this is fundamentals of cations exchange... for every 1 calcium (ca++) or 1 magnesium (mg++) ion absorbed, the root releases 2 hydrogen (h+) ions.

thus, absorbtion of cation makes ph decrease, or become more acidic. why >ph as ammonium nitrgen 'n' is used by plant. (recalling that ph is measured via # of h+ ions in solution...). also, as plant absorbs nitrates and phosphates, more hydroxyl (0h-) and bicarbonates (hc03-) [recall baking soda to raise ph...]. why <ph when nitrate nitrogen 'n' used by plants.

acids have excess (h+) hydrogen cations. immediately released in solution and seek negative charges strongly.

humic acids (humates) work as buffers, and chelate metals and make them able to transport nutes thru cell walls. may be good idea to add humic+fulvic acids to nutes.

coco
~ph=6.2
porosity=90%
air space=10%
solid gr/cm^2=.08
moisture=75%

growers information article, coco coir
http://www.progressive-growth.com/article-coco-coir.php:

Some coirs have been chemically treated, this is most often the case with loose pre-hydrated varieties versus compressed blocks. The treatment has been done to satisfy the cation exchange capacity (CEC) of the growing media. As a refresher, “cations” are positively charged ions, such as Calcium, Magnesium, Sodium, and Potassium. This means that the growing media will hold these ions in a matrix, releasing them as required by plants. There is one slight drawback to this. Until the cation exchange capacity of the growing media is filled, the growing media may hold positively charged nutrient ions, most notably calcium, in reserve, making them less available to plants. However, the cation exchange capacity (CEC) of the coir media is quickly filled, and actually assists calcium absorption in the crop cycle. To ensure optimum availability of all nutrients, supply additional calcium during the first week of growth or during the hydrating process of the coconut coir. Calcium supplement products are ideal for this. Some nutrients specifically formulated for coco tend to have elevated levels of calcium and magnesium while having lower levels of nitrogen.

it would seem apparent that 'exchange' of the 'cations' can easily be done by either hand watering, or automation.

this is why ph drift is really ok thing... just different electrical charges assimilating @ their resonant frequency, as it were, or the ph they function best @.

to answer question, once initial/potential ca 'lock' is broken, should flow ions in/out normally. just be familiar w/ ph rising due to application of cal-mg. plant needs cal in relatively large amounts, so having good buffering, chelating nute good. foliar w/ cal weekly works too... humic+fulvic acids only help... acting as catalyst to charges in media/solution.

ph 5.2-6.5 seems to be specific domain and range of plants. changing ph @ different stages will permit certain charges to be assimilated over others. other threads here on ph changes for flower. but can see that cec and ph are very inter-related...

hope this helps. enjoy your garden!

 

[knna]

Great post, misstress

YosemiteSam, in short: roots uptake those cations bonded to negative colloids of the media (coco), and drop one proton (H+) for each positive charge of the cation (two for Ca and Mg, 1 for K, three for Fe...). When you water with nutes again, those cations has stronger charge than the H+, so they are able to replace them, that goes to the solution, dropping ph.

The high CEC of coco means it has many negative charged colloids, that are able to hold many cations. Thus, it has a high nutes "inertia". Still if you water with plain water for some time, at least cations are still avalaible for the plant for relatively long time. And it means too that drainage Ph and EC isnt a good reference in coco, because it always has higher values than low CEC mediums, and still a drainage EC of 2.5 is normal, while its a warning on a low CEC medium, as perlite.

 

[stoneypenguin]

Great info guys. Never really understood CEC before, but this helps a lot.

 

[YosemiteSam]

Thank you mistress and Knna. That helps a lot, especially the part about how it is actually H cations that get swapped for the nute cations. I am guessing that means when runoff pH stabilizes the the coco cec has been satisfied. Also kinda makes a guy wonder if he shouldn't supplement at least a little Cal/Mag when he plants and/or transplants up to a bigger pot...no doubt depends on his coco, his nutes, etc.

Interestingly enough Knna I basically have a grow where I have Hempy's with pure coco, pure perlite and a mix of the two. I tend to measure pH and EC of runoff just to see what I may see. I feed basically Lucas at around an EC of 2 and let the pH drift from 5.6-6.2. The EC of all 3 of them drifted up to around 2.5-2.6 and I did get a little bit of tip burn on all of them although no other big problems. More interesting, to me, is how EC acts now that I am flushing them with pH'd water only. The EC of the mix (about 30% perlite and the rest coco) dropped the quickest, taking about 3 days to drop below 1. The pure coco dropped second quickest taking about 5 days and the perlite is still around an EC of 1.4 at 5 days.

To be honest the mix is all in 1 gal pots while the 100%ers are in 2 gal pots...so that might account for the difference there. Not sure what to make of the perlite vs coco though but it looks to me like coco is easier to flush (although this is a sample of 1 so statistically it probably means nothing).

Anyways, thanks again for the info. I have a little better understanding now. Appreciate the help.

 

[YosemiteSam]

For the record the plants in perlite are yellowing off first in spite of having the highest EC runoff. The perlite/coco plants are in between and the plants in pure coco are yellowing off the slowest.

Not sure what it means...just an observation.

 

[*mistress*]

For the record the plants in perlite are yellowing off first in spite of having the highest EC runoff. The perlite/coco plants are in between and the plants in pure coco are yellowing off the slowest.

Not sure what it means...just an observation.

"yellowing off"?
is this fan leaves turning yellow during flowering?

 

[YosemiteSam]

actually during final flush...doing it to them on purpose. just seems that it is easier in perlite than coco is all. no big deal either way. a two week flush looks like it is going to work perfectly for the coco plants.

 

[analogue]

Hey Sam it sure takes a while to get Coco to release all it's nutes. It's like trying to take candy away from a baby = baby's fist is clenched tight and won't let go.

I'm on the precipice of two weeks w/ no nutes and the upper leaves aren't quite yellowing yet (although my Bubblegums were over fed). I've run 3x volume through two times other times just really low ppm water (just Canna Boost actually and a little floralicious plus)..

 

[OverGrowRefugee]

cation exchange capacity
ability of media/+nutrient solution to hold positive charges (cations) available for uptake by roots.

cec measurements:
milli-equivalents=the # of charges a cup of media can hold. standard measurement is 100g of media by weight, or 100cc by volume. vermic., perlite, etc. measured by weight instead of volume.

cec 0=media hold no cations available for roots.
cec 100=media holds cations for roots under all conditions.
examples:
peat moss-90 (similar to coco)
vermiculite-20
perlite-0

cations
repel like charges/positively charged ions
hydrogen (h+)
potassium (k+)
calcium (ca++)
magnesium (mg++)
ammonium (nh4+)
iron (fe++)
manganese (mn++)
zinc (zn++)

absorbed mostly on negatively charged surfaces.

anions
attract like charges-negatively charged
nitrates (n03-)
phosphates (hp04--)
sulphates (s04--)
chlorides (cl-)

nutrient example: potassium nitrate. metal cation (k+) bonded to non-metal anion (no3-)=kn03.

almost exclusively in nutrient solution. easily leached away.

plants 'exchange' ions for ions during uptake. for every 1 potassium (k+) or ammonium (nh4+) ion absorbed, 1 hydrogen (h+) ion is released into media+nutrient solution. this is fundamentals of cations exchange... for every 1 calcium (ca++) or 1 magnesium (mg++) ion absorbed, the root releases 2 hydrogen (h+) ions.

thus, absorbtion of cation makes ph decrease, or become more acidic. why >ph as ammonium nitrgen 'n' is used by plant. (recalling that ph is measured via # of h+ ions in solution...). also, as plant absorbs nitrates and phosphates, more hydroxyl (0h-) and bicarbonates (hc03-) [recall baking soda to raise ph...]. why <ph when nitrate nitrogen 'n' used by plants.

acids have excess (h+) hydrogen cations. immediately released in solution and seek negative charges strongly.

humic acids (humates) work as buffers, and chelate metals and make them able to transport nutes thru cell walls. may be good idea to add humic+fulvic acids to nutes.

coco
~ph=6.2
porosity=90%
air space=10%
solid gr/cm^2=.08
moisture=75%

growers information article, coco coir
http://www.progressive-growth.com/article-coco-coir.php:


it would seem apparent that 'exchange' of the 'cations' can easily be done by either hand watering, or automation.

this is why ph drift is really ok thing... just different electrical charges assimilating @ their resonant frequency, as it were, or the ph they function best @.

to answer question, once initial/potential ca 'lock' is broken, should flow ions in/out normally. just be familiar w/ ph rising due to application of cal-mg. plant needs cal in relatively large amounts, so having good buffering, chelating nute good. foliar w/ cal weekly works too... humic+fulvic acids only help... acting as catalyst to charges in media/solution.
View Image
ph 5.2-6.5 seems to be specific domain and range of plants. changing ph @ different stages will permit certain charges to be assimilated over others. other threads here on ph changes for flower. but can see that cec and ph are very inter-related...
View Image
hope this helps. enjoy your garden!

Great post, misstress

YosemiteSam, in short: roots uptake those cations bonded to negative colloids of the media (coco), and drop one proton (H+) for each positive charge of the cation (two for Ca and Mg, 1 for K, three for Fe...). When you water with nutes again, those cations has stronger charge than the H+, so they are able to replace them, that goes to the solution, dropping ph.

The high CEC of coco means it has many negative charged colloids, that are able to hold many cations. Thus, it has a high nutes "inertia". Still if you water with plain water for some time, at least cations are still avalaible for the plant for relatively long time. And it means too that drainage Ph and EC isnt a good reference in coco, because it always has higher values than low CEC mediums, and still a drainage EC of 2.5 is normal, while its a warning on a low CEC medium, as perlite.

so how long does it take to flush coco with such a high CEC ?

 

[Treetroit City]

so how long does it take to flush coco with such a high CEC ?

aaaaaaaa

 

[Weeded1s]

So In lamens terms...feed your coco first.. then transplant and poor some feed through again to water plant not the coco. BOOm