Diagnosing soil acidity in crops

There are two main categories of acid soils in Western Australia (WA):

1. Soils where acidification from agriculture is affecting production.
2. Soils that were naturally highly acidic before agriculture: 'Acid wodjil' soils in the east/north-east wheatbelt and acid peaty soils in the south-west.


Roots are shortened (left) where they meet the acidic layer.
Canola response to incorporated lime strip

What to look for


  • Growth and yield varies with soil type usually worse on acidic sandy surfaced soils.


  • Shortened roots, often with thickened ends where they meet the acidic layer, generally below 10 centimetres (cm).
  • Reduced growth and tillering.
  • Premature maturity and reduced yields, particularly in seasons with a dry finish where plants rely more on stored subsoil water for grain filling.
  • Subsoil moisture below the root zone of maturing crop.
  • Soil acidity reduces molybdenum availability and to a lesser extent nitrogen, sulphur, phosphorus, calcium and magnesium availability.
  • Soil acidity in the surface reduces nodulation in legumes.

What else could it be

Condition Similarities Differences
Diagnosing sandplain traffic pan Reduced root growth in compacted layer. Often occurs with soil acidity Identified by the presence of acidity by soil test and compaction by probe or penetrometer
Diagnosing spring drought in wheat and barley Can have similar plant symptoms Causes can be determined by the soil type and location.
Diagnosing boron toxicity in wheat Can have similar plant symptoms Boron toxicity only occurs on highly alkaline clay soils.
Root diseases and root chewing insects
Weak plant and/or older leaf death Root lesions or chewing

Where did it come from?

  • Soil acidification occurs naturally very slowly as soil is weathered but is accelerated by productive agriculture.
  • Soil acidifies because the concentration of hydrogen ions in the soil increases.
  • In WA the two main causes of soil acidification are inefficient use of nitrogen and export of food and fibre from the farm.

Management strategies

Spreading lime
Spreading lime
  • Liming is the most economical method to ameliorate soil acidity. The amount of lime required will depend on the soil pH profile, lime quality, soil type, farming system and rainfall.
  • Liming is not economic for acid wodjil soils, although there has been some success with deep banding lime to increase rooting depth.
  • Planting acid-tolerant plants such as serradella, triticale, wodjil yellow lupins and using molybenum seed treatments are an option however as acidification is on-going, these must be used in conjunction with liming.

How can it be monitored?

Soil test
Soil test
  • Select sites according to the main soil types in a paddock, accurately identify the location and resample areas at risk every four years.
  • Sampling 0-10,10-20 and 20-30cm soil layers is necessary to detect topsoil and subsurface soil acidity. A 5cm diameter exhaust tube, marked in 10 cm increments is a suitable tool.

Where to go for expert help

+61 (0)8 9368 3493
Page last updated: Tuesday, 20 January 2015 - 9:48am