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You have high soil pH now what?

When it comes to high pH there are no easy fixes. Understanding why you have high pH is the first step to increasing production.

Soil pH is the measure of potential Hydrogen. It is simply a measure of how much hydrogen is in the soil and tells you nothing else. It has nothing to do with whether you have high or low levels of cationic nutrients.

In high pH we are measuring the OH ion. That ion can be tied to a limitless number of other ions, such as nitrogen, potassium, magnesium, sodium, or calcium to name a few.

Here is a quick rundown of soil compounds that cause high pH.

The Carbonate (CO3) molecule can also be a source of high pH soil. Carbonates can occur in high pH soils that have low oxygen and high carbon dioxide (CO2) levels. Water (H2O and CO3 interact to from OH ions and CO2. In aqueous solution, carbonate, bicarbonate, carbon dioxide, and carbonic acid exist together in a dynamic equilibrium. In strongly basic conditions, the carbonate ion predominates.

Potassium Hydroxide (KOH) – Is an extremely strong base. KOH becomes tacky in air because KOH is hygroscopic.  KOH generally contains varying amounts of water as well as carbonates. Adding potassium chloride (muriate of potash) to wet soil increases soil KOH, making soil higher in pH. If potassium is needed in high pH soils it is best to use a potassium sulfate. To reduce soil KOH use a fertilizers that create sulfuric acid.

Potassium Carbonate (K2CO3) - Is a white salt, soluble in water which forms a strongly alkaline solution. It is hygroscopic. Soils high in KOH and have poor aeration can lead to increased amounts of Potassium Carbonate It is a main component of soap, and is correlated with reduced biological activity. Keeping soil oxygen levels up and avoiding KCl fertilizer applications will reduce potassium carbonate build up.

Sodium hydroxide (NaOH) - Also known as lye, is a common component of drain cleaners. Sodium hydroxide forms a strong alkaline solution when dissolved in a solvent such as water. It is hygroscopic and readily absorbs carbon dioxide from the air further increasing soil pH. A sodium hydroxide solution will leave a yellow stain on fabric and paper.

Sodium bicarbonate (NaHCO3) - Is formed by combining sodium hydroxide and carbon dioxide. Aqueous solutions are mildly alkaline: Sodium bicarbonate may also be used as an anti-fungal. It has disinfectant and antiseptic properties. Keeping soil oxygen levels up, limiting raw manure applications, and using sulfate containing fertilizers will help to reduce sodium soil levels.

Magnesium hydroxide (Mg(OH)2 ) – Is best known for low solubility, and is considered a strong base. Magnesium hydroxide interferes with the absorption of folic acid and iron, necessary crop nutrients.

Magnesium Carbonate (MgCO3) – Is formed by combining Mg(OH)2 and CO2. It is practically insoluble in water and ammonia. All forms of magnesium carbonate react in acids. Due to its insolubility, high magnesium soils often have magnesium deficient crops growing on them. MgCO3 is a potent liming agent, but should be used with caution to avoid build up of magnesium in soils. MgCO3 is hygroscopic and can cause soils to stay wet and sticky.

Calcium Hydroxide (Ca(OH)2) is formed in soils by that have calcium chloride (by product of KCl) and an aqueous solution of sodium hydroxide present. In some cases calcium hydroxide can be a flocculent.




Additional Info

  • Article Reference:: Calcium Products, Inc.
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