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Colorado Hail, CO. Elev. 5,900 FT

Who can fully explain how salts affect the soil.

I understand quite a bit of the way chemical fertilizers leave salts, but I'm confused on how organics can leave high salts {manures and compost}. Since I never paid attention in chemistry class years ago, I am pretty much a dumb ass when it comes to this aspect of growing.

I know I should know this, and I have tried to read up on it, but I could use an english explaination of how this happens. Perhaps a link or two to a good web site will help as well, something easy to comprehend...

"The only dumb questions are the ones not asked"

5/24/2004 9:18:25 AM

I'm with Gordon... GO UTES!

For what it's worth, I have the same problems and questions...

5/24/2004 10:37:01 AM

Puyallup, WA

I have found that pumpkin plants are very salt tolerant. I had readings over 5.0!!! They will come down over the winter. Now at 2.3.

5/24/2004 10:40:06 AM

[email protected]

AG's are salt tolerant compared to other crops.

All nutrients are salts. Roots have salts in them. This creates "Osmotic pressure" on the soil solution (water in the soil with dissolved nutrients). Since water is drawn toward salt, the less salty soil solution passes through the root which is little more than a semi-permiable membrane.

But if the salts in the soil solution are greater than the salts in the root hair, the process is reversed. This is called "reverse osmosis" where the water in the roots gets yanked back toward the soil. In laymans terms, we know this to be "fertilizer burn" or "salt damage". The damage is identical regardless of the source of salts.

5/24/2004 12:15:14 PM

Dagobah Ohio, USA

With the use of chemical or salt ferts, its important to understand the properties of leeching. For a more detailed perspective, do some reading on ion exchange between nutrients and the soil medium. Helps to understand salinity too. Borders, Barnes & Noble has some great books.

I'll get right to the point. Some soil components have a high "CATION EXCHANGE CAPACITY" which allows higher levels of nutrients to adhere to soil particles until dissolved in water for plant uptake. A medium with high Cation Exchange Capacity will act much like long term storage for nutrients. This is great for slow release or low concentration organics or, if you water every couple days but only fert every couple weeks.
But.

continued:

5/24/2004 12:46:49 PM

Dagobah Ohio, USA

In the context of Salt/Chemical ferts, I will focus on underlying strategy of high dosage-rapid release liquid fertilizers. With these ferts, if you aren't careful, the salt content can get very high, and quickly. Even more so if you have low humidity and high evaporation rate. (This isn't the best fert system for an HPS closet grow but is acceptable outdoors due to leeching of the soil by rain. So it would be much safer to use soil components with LOW cation exchange capacity. That simply means that extra nutrients wouldn't be stored as well by the soil, they would just leech out and would prevent salt buildup,(salt buildup limits water uptake) and toxicity which is easy to do with concentrated liquid ferts.

The salt index is a rough barometer of a fertilizer's potential to prevent water absorption from the soil by plant roots. This is in comparison to the potential of an equal weight of Sodium Nitrate, which is therefore given a value of 100. Obviously, a high index has greater chance of freaking your plants! Sodium Nitrate is pretty risky itself, so if a fert has a rating OVER 100, ya better be darn sure you know what you're doing ;-)

Excessive salt content doesn't just inhibit water uptake, it actually creates reverse osmotic pressure in the root zone which means water is drawn OUT of plant by the roots. Your plants then begin to show symptoms of dehydration or nutrient deficiency when another fert and/or watering is actually the LAST thing it needs!

In general, if you have a fert with a index over 25, be sure to dilute with water. DO NOT apply such ferts right into soil. Here are a few common ones.

Potassium Chloride-116
Ammonium Nitrate -105
Sodium Nitrate -100
Ureas-75
Potassium Nitrate-74
Ammonium Sulfate 69
Calcium Nitrate-53
Potassium Sulphate-46

5/24/2004 12:47:12 PM

Dagobah Ohio, USA

http://ohioline.osu.edu/b472/fertile.html

I would also like to add this to the link above which is an excellent tutorial.

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.
continued:

5/24/2004 1:05:59 PM

Dagobah Ohio, USA

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.

5/24/2004 1:06:11 PM

Ga.

Friendly Pharmeer,,can you break this down to understandable wording for us which dont comprehend??...LOL....

5/24/2004 3:09:30 PM

Wallingford,CT

Jeff, remember the original question above...."fully explain how salts affect the soil. ......an english explaination of how this happens." the simple answere is its like pouring salt on a slug.

5/24/2004 9:16:25 PM

Appalachian Mtns.

Yea, what he said :0)

5/24/2004 9:32:48 PM

Dagobah Ohio, USA

There is no simple answer to the question. If you want to fully understand the answer some research is required.
This link " Ohio State University Website" is related to organic compost only.
http://ohioline.osu.edu/anr-fact/0015.html

The paragraph on soluable salts in particular.
also, Organic Chemical Contaminants, Pathogens, Miscellaneous Characteristics.

5/24/2004 10:06:02 PM