# Lowering pH



## Ridgerunner (May 16, 2017)

Simplified:
The Science.
Plants access cation nutrients through the exchange of hydrogen for the nutrients in the soil and placing those nutrients in the soil solution. In high pH soils, H+ is less available (neutralized) making nutrients less available. (There are important caveats.)
Many high pH soils have a high pH due to the presence of calcium carbonate (CaCO3) in the soil. The carbonate (CO3) interacts with and removes H+. Two H+ atoms will break the Ca bond and combine with the carbonate molecule to produce carbon dioxide (CO2) and water (H2O). The CO2 eventually gasses off and the water and Ca remain in the soil.
In order to prevent carbonate from removing/neutralizing H+ and increase the presence of H+ in the soil and lower soil pH, the calcium carbonate in the soil must be removed/neutralized. This is done by adding a source of hydrogen to the soil.
One method of adding H- to soil is through the application of sulfur (S), soil bacteria through a rather complicated process, produce sulfuric acid (H2SO4). The H2SO4 dissociates into sulfate (SO4) and 2 atoms of H+. The 2 hydrogen atoms interact with the CaCO3 and neutralize the CO3. Consequently, adding one atom of of sulfur will neutralize one molecule of of CaCO3. On a weight to weight basis, this is a 3.12 to 1 ratio. That is, every one pound of sulfur will neutralize 3.12 lbs of CaCO3. To reach a pH 7 (neutral pH) all of the CaCO3 in the soil must be neutralized (i.e. all of the carbonate must be removed. Once that is accomplished, then the addition of H+ will begin to lower pH below pH 7. There is no accurate method for determining soil carbonate based on a soil pH test alone. Many soil test labs can provide a soil carbonate test and report the carbonate content of soils in the form of a percentage by weight.

The Math:
As an example, if a lab does a carbonate test and the results are that the soil has a CaCO3 content of 2.5 %:
An acre of soil is assumed to contain 2,000,000 lbs of soil.
2.5% of 2,000,000 is 50,000 lbs per acre (or 1148 lbs/M) of calcium carbonate (CaCO3 or lime).
To determine the amount of sulfur (S) require to neutralize that amount of CaCO3/lime, divide by 3.12. 368 lbs of S/M will be needed to lower pH of the soil to pH 7. 
Disregarding the impact that will have on the soil environment and biological habitat, the cost per thousand square feet will be nearly $140. 
There are other methods, that although the won't "permanently" change soil pH, can produce improve nutrient availability.

Soil pH maps:
http://www.bonap.org/2008_Soil/SoilTypesRelatedMaps.html


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