Management of soil acidity

Land managers can manage soil acidity by raising the pH to a desired value through several methods:

• Flooding: In lowlands systems, flooding may be an effective technique in raising the pH of the soil. However, this effect is only good for the time for which the soil is flooded. Flooded or paddy mineral soils are ‘self-liming’. When they are flooded and become anaerobic (lack of oxygen in the soil atmosphere) for a period of time, the pH rises toward neutrality even when the soil pH was originally acidic. If the soil is subsequently drained and becomes more aerobic (more oxygen in the soil atmosphere), the pH will return to an acidic state
  • However, care must be taken if the soil contains manganese-oxide minerals, since flooding conditions may lead to manganese toxicity.
  • Crop consideration is also required. Flooding conditions reduces the oxygen within the soil, which is needed for plant life. As a result, crops that do not tolerate high amounts of water and low oxygen levels are not be suited for flooded conditions. Taro and rice are examples of crops that grow well in flooded lowlands.
    
• Additions of organic matter: Additions of organic matter is a viable option to manage problems associated with soil acidity.
  • Organic matter increases the cation exchange capacity of the soil. As the base saturation increases, the relative amount of “acid cations” decreases.
  • In addition, organic matter forms strong bonds, known as “chelates,” with aluminum. Chelation reduces the solubility of aluminum and soil acidity. Again, if your soil is prone to manganese toxicity, it is not suggested that you add organic matter.
    
• Additions of wood ash: Like organic mater, wood ash increases base saturation and forms chelates with aluminum.
  
• Conventional Liming: Various liming materials may be added to the soil that neutralize, or counteract, soil acidity. Liming materials are bases that react with hydrogen ions in the soil solution to form water?
  • Examples of common liming materials are limestone (calcium carbonate), dolomite (calcium/magnesium carbonate), hydrated lime (calcium hydroxide), and quicklime (calcium oxide). Calcium and magnesium silicates are also used as liming agents.