Holy crap...coir sucks vs. peat...wow!

[gojo]

OK,

It's time to :horse: for the last time...it looks like peat is superior to coir as a planting medium. I always thought coir was superior to peat but after reading a post by c-ray I did more research. I never like peat cuz' it's environmental issues but it looks like if you can source *non*-reed or sedge peat your all good :allgood2:

Read this...it's even got pics! (PDF) (http://www.usu.edu/cpl/PDF/CoconutCoirPaper.pdf)

:D

[purplehaze2]

yea thats a big difference ,50%peat and 50% pearlite kicked ass. hands down!

[islandgrow]

well coir only holds 4x its weight in water? correct? and provides aeration? and peat holds 20x its weight, but I thought it provided less aeration, and more water retention.

[Lungus]

I've been recently growing in organically amended peat and coco and could see no appreciable difference between the two except the coco was lighter and stayed loose and didn't compact like the peat. I also add perlite to the coco to keep it light and airy.

[ghostryder]

i tried them both and i know coco is great for hydro but for cloning i'll stick with the peat. i also swear by the soil-less medium with 25% perlte but then i do terrapots.

[crazy cooter]

I gotta disagree brother Mojo... I ran coco/compost/perlite this Spring and have been amazed by the results. No super-duper growth rates or anything, just very easy to use, drainage is great, impossible to overwater young plants, no pH swings, root growth/density is unbelievable. I really like it. :)

[gojo]

Hey all :D

well coir only holds 4x its weight in water? correct? and provides aeration? and peat holds 20x its weight, but I thought it provided less aeration, and more water retention.

Your are correct which is why peat is amended with perlite...but I would suggest using Turface MVP instead of perlite. Turface MVP is a better replacement for perlite and it holds it's own weight in water without expanding in size...good for OD grows!


I've been recently growing in organically amended peat and coco and could see no appreciable difference between the two except the coco was lighter and stayed loose and didn't compact like the peat. I also add perlite to the coco to keep it light and airy.

How are you growing? Indoor or OD? Drip, hydro, hand water? Did you add perlite to the peat also?

Coir is a better medium for hydro/drip than it is for soil or soilless hand water or OD grows mostly due to it's air/h20 ratios.


I gotta disagree brother Mojo... I ran coco/compost/perlite this Spring and have been amazed by the results. No super-duper growth rates or anything, just very easy to use, drainage is great, impossible to overwater young plants, no pH swings, root growth/density is unbelievable. I really like it.

Yea thats some benefit of coir: hard to over water (but it also is more hydrophobic than peat), more stable PH and greater air/h20 ratios is good for roots...but that's vanilla coir vs vanilla peat. I would think the compost you added to your mix acted as peat in terms of water retention and adhesion.



----------------------------------------

I'm not saying coir sucks in general, just that when compared to peat with all other factors being equal, peat is the superior planting medium...especially for cannabis. Now I'm not saying you can't grow GREAT cannabis in coir, you can, it's just that peat will provide better results (even in incremental terms).

One thing I really like about provable experiments following the scientific method is they provide a much more factual (ie. provable and reproducible) results...I'm not saying that everyone's personal experience doesn't matter, they do, it's just that everything is so subjective...different strains, grow rooms, temps, etc, etc, etc. This is even more exaggerated when different grows are compared and because ppl are not using the same methods of testing and measurement...kinds like apples to oranges.

-----------------------------------------

P.S.
I changed the wording my thread starting post...I think "coir is a crappy medium for horitculural use" is too harsh and does not accuratly describe the scientific studies (or my personal opinions) of peat vs. coir. So now it reads "it looks like peat is superior to coir as a planting medium."


Thanks all! :D :D :up:

[Lungus]

I'm growing indoors and hand watering. I add worm castings, kelp meal, cottonseed meal and other stuff to the coco and it performs as well or better than when I did the same thing with peat pro mix.

[gojo]

cool, i really like how coir is more environmentally friendly :D :up:

[Lungus]

cool, i really like how coir is more environmentally friendly :D :up:
I like it because, from what I understand I have yet to do it, I can recycle it through a few crops before it breaks down. That means less work for me with the hauling out of used pro mix and hauling in new bales, I just re-amend the coco and away we go again. Actually I have one batch of coco with plants in it and one batch of coco that sits and "cooks" breaking down the different meals and getting the microlife into high gear.

[gojo]

I can recycle it through a few crops before it breaks down.

That is a VERY important point regarding soil structure that many ppl don't consider. Organics matter (coir and peat, etc) will break down over time which will increase the Perched Water Table (PWT) of the soil which in turn makes the soil anaerobic thus injuring/killing the roots...and at the least def. slowing growth , yeild, etc,etc.

If you use ACT and/or A/EM then I would suggest you do not reuse your soil. Those BMO (benifical microorganisms) will break down peat pretty fast and coir is a bit slower but they both decompose into a soup like material (to that roots that is)...this can happen after a say 6+ months so it's best to only use it for one OD grow or two shorter flowering ID grows (if use add BMO).

one batch of coco that sits and "cooks" breaking down the different meals and getting the microlife into high gear.

You may not want to let it 'cook' for more than a few weeks. I usually pre-mix my soilless (I include Biozome and living worms) and water it with ACT, AEM and a protozoa infusion (I grow them in fish tanks) then I let it sit for about 2 weeks to build up life as you mentioned. :up:

P.S.
Cray and I have a REALLY EXCITING project underway that will change how we make our mixes...base it on science with lab coats and beakers!!! News by the first week in June! :D


Here's some great info by a rather curious bonsai farmer who goes by "Al" (he doesn't like those with different opinion's than his own and ESPECIALLY doesn't like those with a deeper knowledge than his own ;) ...but he's useful for at least the following info):
Container Soils - Water Movement and Retention

A Discussion About Soils

As container gardeners, our first priority should be to insure the soils we use are adequately aerated for the life of the planting, or in the case of perennial material (trees, shrubs, garden perennials), from repot to repot. Soil aeration/drainage is the most important consideration in any container planting. Soil is the foundation that all container plantings are built on, and aeration is the cornerstone of that foundation. Since aeration and drainage are inversely linked to soil particle size, it makes good sense to try to find and use soils or primary components with particles larger than peat. That components retain their structure for extended periods is also extremely important. Pine and some other types of conifer bark fit the bill nicely and I’ll talk more about them later.

The following also hits pretty hard against the futility of using a drainage layer in an attempt to improve drainage. It just doesn't work. All it does is reduce the amount soil available for root colonization. A wick will remove water from the saturated layer of soil at the container bottom. It works in reverse of the self-watering pots widely being discussed on this forum now.

Since there are many questions about soils appropriate for use in containers, I'll post basic mix recipes later, in case any would like to try the soil. It will follow the Water Movement info.

Consider this if you will:

Soil need fill only a few needs in plant culture. Anchorage - A place for roots to extend, securing the plant and preventing it from toppling. Nutrient Sink - It must retain sufficient nutrients in available form to sustain plant systems. Gas Exchange - It must be sufficiently porous to allow air to the root system and by-product gasses to escape. And finally, Water - It must retain water enough in liquid and/or vapor form to sustain plants between waterings. Most plants could be grown without soil as long as we can provide air, nutrients, and water, (witness hydroponics). Here, I will concentrate primarily on the movement of water in soil(s).

There are two forces that cause water to move through soil - one is gravity, the other capillary action. Gravity needs little explanation, but for this writing I would like to note: Gravitational flow potential (GFP) is greater for water at the top of the container than it is for water at the bottom. I'll return to that later. Capillarity is a function of the natural forces of adhesion and cohesion. Adhesion is water's tendency to stick to solid objects like soil particles and the sides of the pot. Cohesion is the tendency for water to stick to itself. Cohesion is why we often find water in droplet form - because cohesion is at times stronger than adhesion, water’s bond to itself can be stronger than the bond to the object it might be in contact with; in this condition it forms a drop. Capillary action is in evidence when we dip a paper towel in water. The water will soak into the towel and rise several inches above the surface of the water. It will not drain back into the source. It will stop rising when the GFP equals the capillary attraction of the fibers in the paper.

There will be a naturally occurring "perched water table" (PWT) in containers when soil particulate size is under about .125 (1/8) inch.. This is water that occupies a layer of soil that is always saturated & will not drain from the portion of the pot it occupies. It can evaporate or be used by the plant, but physical forces will not allow it to drain. It is there because the capillary pull of the soil at some point will surpass the GFP; therefore, the water does not drain, it is "perched". The smaller the size of the particles in a soil, the greater the height of the PWT.

If we fill five cylinders of varying heights and diameters with the same soil mix and provide each cylinder with a drainage hole, the PWT will be exactly the same height in each container. This saturated area of the pot is where roots seldom penetrate & where root problems frequently begin due to a lack of aeration. Water and nutrient uptake are also compromised by lack of air in the root zone. Keeping in mind the fact that the PWT height is soil dependent and has nothing to do with height or shape of the container, we can draw the conclusion that: Tall growing containers will always have a higher percentage of unsaturated soil than squat containers when using the same soil mix. The reason: The level of the PWT will be the same in each container, with the taller container providing more usable, air holding soil above the PWT. Physiology dictates that plants must have oxygen at the root zone in order to maintain normal root function.

A given volume of large soil particles has less overall surface area when compared to the same volume of small particles and therefore less overall adhesive attraction to water. So, in soils with large particles, GFP more readily overcomes capillary attraction. They drain better. We all know this, but the reason, often unclear, is that the height of the PWT is lower in coarse soils than in fine soils. The key to good drainage is size and uniformity of soil particles. Mixing large particles with small is often very ineffective because the smaller particles fit between the large, increasing surface area which increases the capillary attraction and thus the water holding potential.

When we add a coarse drainage layer under our soil, it does not improve drainage. It does though, conserve on the volume of soil required to fill a pot and it makes the pot lighter. When we employ this exercise in an attempt to improve drainage, what we are actually doing is moving the level of the PWT higher in the pot. This simply reduces the volume of soil available for roots to colonize. Containers with uniform soil particle size from top of container to bottom will yield better and more uniform drainage and have a lower PWT than containers with drainage layers. The coarser the drainage layer, the more detrimental to drainage it is because water is more (for lack of a better scientific word) reluctant to make the downward transition because the capillary pull of the soil above the drainage layer is stronger than the GFP. The reason for this is there is far more surface area for water to be attracted to in the soil above the drainage layer than there is in the drainage layer, so the water "perches".

I know this goes against what most have thought to be true, but the principle is scientifically sound, and experiments have shown it as so. Many nurserymen are now employing the pot-in-pot or the pot-in-trench method of growing to capitalize on the science.

If you discover you need to increase drainage, you can simply insert an absorbent wick into a drainage hole & allow it to extend from the saturated soil to a few inches below the bottom of the pot, or allow it to contact soil below the container where it can be absorbed. This will successfully eliminate the PWT & give your plants much more soil to grow in as well as allow more, much needed air to the roots.

Uniform size particles of fir, hemlock or pine bark are excellent as the primary component of your soils. The lignin contained in bark keeps it rigid and the rigidity provides air-holding pockets in the root zone far longer than peat or compost mixes that too quickly break down to a soup-like consistency. Conifer bark also contains suberin, a lipid sometimes referred to as nature’s preservative. Suberin is what slows the decomposition of bark-based soils. It contains highly varied hydrocarbon chains and the microorganisms that turn peat to soup have great difficulty cleaving these chains.

In simple terms: Plants that expire because of drainage problems either die of thirst because the roots have rotted and can no longer take up water, or they starve/"suffocate" because there is insufficient air at the root zone to insure normal water/nutrient uptake and root function.

To confirm the existence of the PWT and the effectiveness of using a wick to remove it, try this experiment: Fill a soft drink cup nearly full of garden soil. Add enough water to fill to the top, being sure all soil is saturated. Punch a drain hole in the bottom of the cup & allow to drain. When the drainage stops, insert a wick into the drain hole . Take note of how much additional water drains. Even touching the soil with a toothpick through the drain hole will cause substantial additional water to drain. This is water that occupied the PWT before being drained by the wick. A greatly simplified explanation of what occurs is: The wick "fools" the water into thinking the pot is deeper, so water begins to move downward seeking the "new" bottom of the pot, pulling the rest of the water in the PWT along with it. If there is interest, there are other simple and interesting experiments you can perform to confirm the existence of a PWT in container soils. I can expand later.

I remain cognizant of these physical principles whenever I build a soil. I haven’t used a commercially prepared soil in many years, preferring to build a soil or amend one of my 2 basic mixes to suits individual plantings. I use many amendments when building my soils, but the basic building process starts with conifer bark and perlite. Sphagnum peat usually plays a minor, or at least a secondary role in my container soils because it breaks down too quickly and when it does, it impedes drainage and reduces aeration.

Note that there is no sand or compost in the soils I use. Sand, though it can improve drainage in some cases, reduces aeration by filling valuable macro-pores in soils. Unless sand particle size is fairly uniform and/or larger than about ½ BB size I leave it out of soils. Compost is too unstable for me to consider using in soils. The small amount of micronutrients it supplies can easily be delivered by one or more of a number of chemical or organic sources.

[crazy cooter]

Wow- great read. Can you PM me pretty please with where this discussion is taking place so I can go read more?

[plantbuilder]

http://davesgarden.com/community/forums/t/719569/

[crazy cooter]

Ahhh... I'm at Dave's all the time, actually. Haven't run across that Al guy. Must be a little bonsai niche on that site that I don't go into?

Gracias pb.

[gojo-redux]

Hey budy CC :D

NOTE: I am using this nic "gojo-redux" until I get back home cuz I don't have my passphrase for gojo with me :bang:

THe site where I got this info is called gardenweb and it's not a pay site (paysites IMVHO are a fuc*ing rip off and a security risk...shouldn't have to pay for knowledge).

The site PB liked to "Daves Garden" (http://davesgarden.com/community/forums/t/719569/) gets on my nerves cuz' it costs money and 90% of the info is BS from ppl who don't know shit...especailly about high-tech cannabis growth. :farm: (Note to PB: I didn't mean you are included in my description of davesgarden, you are great, davesgarden is not.)

GaredenWeb (http://www.gardenweb.com/) is the site I visit an occasion to lurk and is where I found the infamous Al... TO all CW members: Do not talk about cannabis on that site!!!


Crazy Cooter, here is the sub-forum you'r looking for:
The GardenWeb's "Continer sub-forum" (http://forums2.gardenweb.com/forums/contain/?). Look for posts by "Al" and "JustAnotherGuy2" (JAG2), they are both knowledgeable and helpful when they don't feel threatened by those who have a deeper knowledge than their own. I think they like to be "king of the hill" on the GardenWeb container forum. Though JustAnotherGuy2 is very nice, very knowledgeable and open-mined...unlike "evil Al" ;). A crappy thing about the container forum is most of the members are very, very simplistic in there knowledge and care about organic gardening...they think Al is god and so does he....to bad they are all wrong...Al is a niche guy, he knows about soil but only pine fine/turface types of soil...he's lost when the topics get in depth in regards to true horticultural theory and experimentation...

Crazy Cooter, here is the thread you'r asking about:
"Container Soils - Water Movement & Retention V" (http://forums2.gardenweb.com/forums/load/contain/msg0420085231701.html?43)...Their are four previous iterations of the 'soil' thread, all with very similar thread starting posts but different responding posts (an exception is "Al's mix" was a bit different in volume I&II). At GW each thread can have up to 150 posts before it is closed. Al has had to make 5 iterations of his soil thread (I-IV) because each thread reached it's limit of 150 posts. I would suggest reading volume V, the one I linked for you.

Unfortunitly "Al" didn't like that I was talking outside his limited comfort zone and he become upset...I thought he could hold a rational conversion about organics and changes to his "Al's mix" but I was wrong ;) This is really too bad cuz' I would have liked to form a friendship with him, I'm sure he's got more useful info...that's why I love the power of the lurking! :ninja:

If you want to see my posts in the thread "Soils - Water Movement & Retention V (http://forums2.gardenweb.com/forums/load/contain/msg0420085231701.html?43)" just go towards to bottom and find the posts by "gojosan", they are the longer posts ;) and easy to see...then for a laugh read the resulting posts by other members such as:

Hey Al, With your bday and the long posts from Gojo, I am wondering if you saw my previous post
and
Oh, yes. "That" post. All the talk of cytokynins (sp?) made my head spin. LOL...LOL :D...I should explain AEM to them! HAHAHA!!!



You know what annoyed me the most about that gardenweb forum was that Al accused me of being someone I am not. Someone who follows him around in other forums acting as a troll...yea right, me a troll, like i have the time or inclination! :rofl: haha. He got me confused with someone else and publicly dissed me and said he wouldn't answer my questions. So I responded that I was not the guy he thought I was. But then "magically" both our posts were deleted from the forum...like I said, he just can't take it when someone has a deeper knowledge than his own.

FYI Crazy Cooter, I would not bother posting in that forum, you know more than they do. I will never again post in that forum....they are elitists even though they are poppers in terms of advanced organic and inorganic horticultural knowledge.


But I did write two other threads on that forum that I think will be useful to CW members, especially those doing outdoor...my threads are all about water retention and conservation. Both threads have been already posted here in one way or anther but the newest posts have nice congruity.

CHeck out these threads of mine on GW:
1. Attn Al: Amending youir mix for semi-arid/drought conditions? (http://forums2.gardenweb.com/forums/load/contain/msg05023002464.html?9)


2. 'Wick-Tube': Low-tech/cost auto-watering/drought system (http://forums2.gardenweb.com/forums/load/contain/msg050146536217.html?3)


Also, CHeck out these threads which are pretty usefull too:
1. Al, do you have a 'Watering 101' post somewhere?
(http://forums2.gardenweb.com/forums/load/contain/msg0416453111590.html?32%22]Al,%20do%20you%20have%20a%20'Watering%20101'%20pos t%20somewhere?)

2. RE: Ratio of Turface to Bark & Additional Qs (http://forums2.gardenweb.com/forums/load/contain/msg0518424726437.html?11)


But like I said, and C-ray and I are working on a soilless mix with scientific testing and verified levels of CEC, air porosity, EC, etc, etc, etc....this mix will blow the shit out of all other current soil/soilless mixes....I just need to pay the lab to run all my tests...shouldn't be more than $300-400.00 or so. Then after a bit of R&D Ill post a how-to thread :D :D ...screw AL and his attitude!


HTH :D

P.S.
Crazy Cooter: If you want to find out what Cray and I are working on you can PM me and I'll go into further detail...or just wait untill fist week or so in June and the mix should be done and ready for outdoor/indoor use...I'll write up a indepth how-to thread!!! :D :D :up:

[crazy cooter]

You rule, gojo. Thank you for taking the time to humor me. Much of that stuff is over my head, but I'm learning all the time.

Would love to learn more about what you and C-ray are up to, for sure. C's got another project in the works with an ETA of June that I'm interested in. :woohoo: Look for a PM from me. For some reason I have heartburn tonight and need to smoke a bowl and go find a more comfortable posture than this stool in front of my computer.

Vielen Dank, gojo! :peace:

Crazy Cooter

[dusty]

Yea I love Pro Mix HP. I love the way the pallets looked stacked nicely at my storage house all wrapped and glittering with their MycoRise Inside!

I love how when I apply 10% organic matter and 15% #4 perlite by volume in to my raised beds with the ProMix HP my plants are green from top to bottom till the end and make huge flowers.

Yes...I love peat.

People like Coco because they can say shit like Coco Mofo or Coco Loco or Coco Joke-O ..if you ask any of them why they like coco more than what they were already doing or why they started with it if they haven't used anything else before none of them have a viable "scientifically" backed response...put it in quotes cause it doesn't even need to be exact...Don't even get a "Switched cause I think I can water less..." type response...just "Saw XYZ's pOST LOLLOL!R OMFG IM A GROW KIDDIE LOL!"

[crazy cooter]

That's a whole buncha bullshit right there, dusty. ^^^^ :farm:

It's obvious to any of us actually reading and experimenting with both that both media have their advantages and drawbacks.

It's certainly not worth offending our fellow gardeners over.

Peace-

CC

[dusty]

Um, no it's not. It's the truth.

[crazy cooter]

Um, no it's not. It's the truth.

Oh. Well, in that case...

[nuggdigger]

http://www.sfgate.com/cgi-bin/article.cgi?f=/c/a/2007/09/05/HOHTRTMAL.DTL


how about a comparision of the CEC?

peace

[gojo]

http://www.sfgate.com/cgi-bin/article.cgi?f=/c/a/2007/09/05/HOHTRTMAL.DTL


Yea, I don't like the environmental aspects either. But, if you buy Canidan paet moss it's a lot better method of havesting and harvesting in relation to natural peat moss production.


Canadian Peat Harvesting and the Environment (http://www.peatmoss.com/pm-me2.php) by the Canadian Sphagnum Peat Moss Association (CSPMA)


Executive Summary

For generations, growers and gardeners everywhere have used peat or peat moss for a variety of applications. Since the 1940s the Canadian peat harvesting industry has emerged as a significant rural employer and user of peatland resources.

Peat, mainly derived from Sphagnum moss, but also from reed and other sedge deposits across the country, is marketed among many uses as a soil supplement to enhance gardening and as a soil base for greenhouse production. It is one of nature's truly green products offering a large potential of horticulture uses and at the same time can be disposed of without causing any damage to the environment. Peat, in various sizes of compressed packages and bales, has become a readily available product at our local hardware and garden centres. What would spring gardening be like without a few bales of peat moss to dig into your flowerbeds or to plant with some new shrubs or roses? However, consumers of peat moss want to know whether this important soil additive is being harvested and applied in ways that protect the overall resource and the environment.

In 1999, 1.2 million metric tonnes or about 10 million cubic metres of peat were produced in Canada. This volume of peat harvested each year is small in comparison to the estimated 70 million tonnes or more of peat that accumulates naturally each year in Canada. On a volume basis, there are an estimated three trillion cubic metres of peat deposits in Canada. Peat is accumulating nearly 60 times faster than the amount harvested. In 1999, this production was valued at approximately $170 million f.o.b. production site. Canadian Sphagnum peat, regarded as among the best quality peat in the world, is sold to markets in the United States and Japan as well as across Canada. However, Canada has only a very small share of the world market accounting for approximately eight percent of global peat moss used.

The need to protect natural resources and to ensure wise, sustainable use of the environment is greater today than at any point in our history. Like other natural resource sectors, the harvesting of peat moss around the World has attracted the interest of concerned environmental groups, governments and the public.

In early 1991, the Canadian Sphagnum Peat Moss Association (CSPMA), the New Brunswick Department of Natural Resources and Energy, and the Secretariat to the North American Wetlands Conservation Council (Canada), representing the combined interests of industry, government and researchers, initiated the production of the First Edition of this report. This Second Edition updates the status of peat harvesting and environmental issues concerning the use of peat and peat moss in Canada.

At present, less than 17,000 hectares of Canada's 113 million hectares of peatlands are being used for peat or peat moss harvesting. The majority of companies involved in this industry, through their association with the CSPMA, have articulated a policy for the preservation of environmentally sensitive peatlands use and for site restoration or reclamation of harvested sites. The industry, in association with government and non-government interests, environmental groups and universities, has developed a national peatland research strategy to promote awareness of peatland restoration technology and science. On-going research indicates that new and many existing peatland development sites can be revegetated successfully by Sphagnum moss. Sphagnum moss is, with proper site management during and after use, the key peat-forming plant in Canadian peatlands. The CSPMA Preservation and Reclamation Policy urges peat producers to manage peatland after-use, including restoration of harvested bogs to a functioning peatland when harvesting is finished (see policy in Appendix). Older sites can also be reclaimed to valuable agricultural, forestry or wildlife habitat uses.

It is very evident that Canadian peat moss harvesting is not contributing to a decline in peatland functions or values on a national or regional scale in Canada. Site management issues are being successfully addressed by the industry and government regulations. There is room for further growth of the industry in a co-operative, consultative manner with regulators and environmental interests to ensure a balance between the needs of the environment and sustainable development.

The full PDF is HERE (http://www.peatmoss.com/pm-me3.php)







how about a comparision of the CEC?

peace

The cation exchange capacity of the soil (http://www.cannabase.com/cl/bcga/soil/soil.htm#The%20cation%20exchange%20capacity%20of%2 0the) Posted by Orchid man on January 11, 1999 at 18:24:30

When small quantities of inorganic salts, such as the soluble mineral matter of soil and commercial fertilizers, are added to water they dissociate into electrically charged units called ions. The positively charged ions (cations) such as hydrogen (H+), potassium (K+), calcium (Ca++) magnesium (Mg++), ammonium (NH4+), iron (Fe++), manganese (Mn++), and zinc (Zn++) are absorbed mostly on the negatively charged surfaces of the soil colloids (microscopic clay and humus particles) and exist only in small quantities in the soil solution. Thus, the humus-clay colloids serve as a storehouse for certain essential ions (cations). The negatively charged ions (anions), such as nitrates (N03-) phosphates (HPO4--), sulfates (SO4--), and chlorides (Cl-), are found almost exclusively in the soil solution and can therefore be leached away easily with overwatering. The roots and root hairs are in intimate contact with the soil colloidal surfaces, which are bathed in the soil solution, and therefore nutrient uptake can take place either from the soil solution or directly from the colloidal surfaces (cation exchange). The soil solution is the most important source of nutrients, but since it is very dilute its nutrients are easily depleted and must be replenished from soil particles. The solid phase of the soil, acting as a reservoir of nutrients, slowly releases them into the soil solution by the solubilization of soil minerals and organics, by the solution of soluble salts, and by cation exchange. A more dramatic increase in the nutrient content of the soil solution takes place with the addition of commercial fertilizers. As plants absorb nutrients (ions) they exchange them for other ions. For example, for the uptake of one potassium (K+) ion or one ammonium (NH4+) ion, one hydrogen (H+) ion is released into the soil solution or directly into the soil colloids by the process of cation exchange. Similarly, for the uptake of one calcium (Ca++) or one magnesium (Mg++) ion, two hydrogen (H+) ions are released by the root. Thus, as the plant absorbs these essential cations, the soil solution and the colloidal particles contain more and more hydrogen (H+) ions, which explains why the removal of cations (ammonium (NH4+) nitrogen is a good example) by crops tends to make soils acidic, i.e., having a low pH. Also, as the plant (absorbs essential anions such as nitrates (NO3-) and phosphates (HPO4-), the soil solution is enriched with more and more hydroxyl groups (OH-) and bicarbonates (HCO3-), which explains why the removal of anions (nitrate (NO3-) nitrogen is a good example) by crops tends to make soils alkaline, i.e., having a high pH.



Later :D :up: