A recent soil report will show the rate of lime required depending on the soil type, soil pH and crop type. However a soil analysis result is only as good as the sample taken. A sample normally comprises around 1kg of soil which is taken to represent an entire area or field which contains around 1,000t of soil per hectare to a plough depth of 4″ (10cms). It is therefore imperative to obtain as representative a sample as possible or the results will not reflect the nutrient status accurately.
The lime requirement is calculated in the laboratory based on a test that measures the soils buffering capacity. The buffering capacity is a measure of how much lime it takes to change the pH of the soil to the target pH.
Lime contains calcium and magnesium both of which are alkaline. The calcium and magnesium ions replace acidic hydrogen and aluminium ions through cation exchange. The full effects of lime may take two years to have an effect on soil pH.