Lime is used to help control soil pH. pH is a measure of the soils acidity.  It is an indicator of the chemical processes that occur in the soil and can be used as a guide to how suitable the soil is to grow certain plants.  Soil acidification varies between land uses.  However soil acidity can be increased by:

  • High inputs of nitrogen
  • High leaching environment, like a high rainfall
  • High removal of product – plant material or biomass

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An application of 2.5 tonnes per hectare will raise the pH by 0.3 units

Whether soils become acidic depends a lot on their initial pH and their buffering capacity.  Buffer capacity is the soils ability to resist change in pH.  Soils with high organic matter and good cation exchange capacity will often have good buffering capacity.  A sandy soil with low cation exchange capacity will acidify very quickly.

One of the most important things to know is the soil pH trend over time.  If soil pH is a limiting factor then potential production and ultimately farm income will be adversely affected.  Soil pH testing should be done annually. 

Most plants prefer a soil pH over 6.0 but will grow either side of this, although yield may be affected.  Soil pH influences the availability of soil nutrients and how the nutrients react with each other.

At a low pH many essential elements are not available to plants, while other elements like aluminium become available in toxic levels.  Most plant species have a preferred soil pH level with a general optimum soil pH range between 6.0 and 7.0.  Soil biology is also affected by soil pH.  Most soil organisms also function best with a soil pH between 6.0 and 7.0.