Profitability
The profitability of liming will differ according to individual circumstances and many factors need to be taken into account.
Gross margin of the paddock
Compare the potential profits from crops that can be grown when pH is not limiting, compared to low pH constraining both yield and choice of crops/pastures in the rotation. Also consider the ‘lime’ cost of acidity caused by the rotation from nitrogen fertiliser leaching and product removal. Increases in grain yield or pasture production as a result of liming are an indication that productivity has been lost.
Asset value
Liming improves land value. Liming has a long-term value and investment in lime to improve soil pH should be considered in much the same way as fertiliser history when buying or selling farming land.
Lime costs
The pH of the soil profile, lime quality, soil type and farming system will determine the amount of lime required to raise pH to, or maintain pH at, the desired level. For example, clays are slower to acidify but require more lime to lift pH while sands have less capacity to resist pH change but amelioration requires less lime.
Time required to change pH
The initial soil pH and soil type are important. Topsoil pH responds quickly to liming. Surface applied lime usually takes four to seven years to treat acidity in the subsurface layers, provided that sufficient lime is applied to raise and maintain the topsoil pH above 5.5. Limes with a high proportion of fine particles increase pH quicker.
Liming interval
Repeat applications of lime need to be determined by monitoring the change of the soil pH profile over time. The interval will usually be three to seven years depending primarily on initial soil pH and soil type.