The department monitors soil acidity in agricultural areas by comparing actual lime use with:
- the amount of lime needed to balance soil acidification (soils becoming acid over time)
- the amount of lime needed to treat soils that are already acidic.
Annual soil acidification rates in agricultural regions of SA (expressed as tonnes of lime per year needed to balance the acidification process) have been estimated on the basis of agricultural land use intensity and the area of naturally acidic soils.
Direct monitoring of soil acidity would require soil samples from across the state to be collected and analysed on a regular basis. This is not possible due to the enormous cost and effort that would be required.
Soil acidity becomes a serious problem, affecting agricultural production and the environment, when the level of acidity reaches pHCaCl of 5 or less.
The department has assessed the extent of soils that are already acidic from databases of commercial soil testing services that obtain soil samples throughout the state’s agricultural areas for soil fertility analysis. With this information, the amount of lime needed to treat the topsoil layer (0-10cm depth) of the acidic soils has been determined.
Lime sales data (tonnes) has been collected annually from commercial lime product suppliers in South Australia since 1998 to estimate the annual amount of lime applied to land in the agricultural regions.
Soil acidity in the subsurface soil layer (below 10cm) is also an issue of concern in agricultural areas, but very little data is available and this would be very costly to monitor extensively.
Some data on land managers’ awareness and understanding of soil acidity and its treatment is obtained from the the department land manager surveys.