How can substances change the pH of soil?

eg Lime (calcium carbonate) or Dolomitic Lime (Magnesium carbonate) can be added to acidic soils while Iron (II) sulfate or aluminum sulfate can help correct soil that has too much alkalineHow can substances change the pH of soil?
When calcium carbonate or MgCO3 is added to soil, the CO3= ions combine with the naturally occuring H+ ions (derived from water equilibrium ) H2O at equilib with H+ plus OH-



leaving the OH- ions in the water equilibrium to cause the soil to be more alkaline, or if the soil is originally acid containing excess H+ ions, the OH- ions will convert these excess H+ to water.



In the case of soil being to alkali with excess OH- ions, the addition of Fe+2 and Al+3 ions cause just the opposite from the reaction above to happen.



either of the ions will react with any OH- ions in the soil which is making it too alkaline and convert these loose OH- ions into insoluble compounds such as Fe(OH)2 or Al(OH)3 which binds up the OH-, leaving the H+ from the water equilibrium above to show up and increase the acidity of the soil.