Your soil is a valuable asset which, if well managed, can increase the productivity and value of your land. Recognising and managing acid soil and acidifying processes not only helps protect water quality across the catchments, but also helps to maximise productivity and economic returns on your farm.
Acid soil has a pH of less than 7.0. The pH of soil is a measure of its relative acidity or alkalinity. Many of the soils in Sydney's drinking water catchments are highly weathered and naturally acidic, with a pH of less than 5.5.
While different plants have different tolerances to acidity, most agricultural plants do best when the soil pH is between 5.0 and 6.5. But when the pH drops below 5.0, plants that are very sensitive to acidity, such as barley and lucerne, become adversely affected.
Acid soil is a major cause of land degradation in some areas, resulting in a loss of groundcover, increased soil erosion and lower productivity. However, it is a slow and subtle process brought about, in part, by agricultural production.
Agriculture may contribute to soil acidity by:
- lack of deep-rooted perennial grasses to catch nitrogen before it leaches below the root zone (e.g. clover dominant pastures or mainly annual pastures)
- removing alkaline plant and animal produce (e.g. lucerne hay cutting)
- continuous use of fertilisers high in nitrogen (e.g. ammonium sulphate and mono-ammonium phosphate).
Some effects of soil acidity are:
- lower agricultural production rates from less vigorous pasture
- higher production costs (e.g. need to add lime to soil and greater weed control)
- loss of groundcover, leading to soil erosion and lower water quality
- less water use by vegetation, contributing to salinity.
It is important to get advice from a qualified adviser before treating your soil.
What you can do
- Use deep-rooted perennial pastures to improve nitrogen recycling and slow the rate of acidification.
- Use lime to raise soil pH.
- Use plants that can tolerate acid soil.
- Do a LANDSCAN course to learn about your soils.