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Soil Acidity

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Soil acidification is a major soil degradation problem in the South Coast Region (DAFWA, 2013).

A high proportion of soils are either below optimum soil pH or at high risk of acidity for productive agriculture because current commercial crop and pastures species require a near neutral soil pH for optimum production.

 

Causes of soil acidification

Acidification is a natural process and part of normal weathering. However it can be accelerated under agriculture practices by the incomplete cycling caused by (Bolan and Hedley, 2003). The causes of incomplete cycling include:

  • The excretion of hydrogen ions from plants due to greater update of captions than anions
  • Removal of plant and animal products that typically contain high levels of anions
  • Nitrate leaching by the use of ammonium-based fertilisers
  • Nitrogen leaching from the root zone in legume pastures
  • The accumulation of organic matter as humic acids in the soil

 

Diagnosing soil acidity

The only way to diagnose soil acidity is to measure soil pH. Soil samples should be taken at 0-10, 10-20 and 20-30 cm depth to determine a soil pH profile.

Subsurface soil acidity is a growing problem but top soil pH can be quite difference from the subsurface pH and acidity in the subsurface soil cannot be detected or estimated by knowing the topsoil pH (Gazey et al., 2014)

 

Reducing the impact of soil acidity

Where soils are at risk of becoming acidic, the future impact of soil acidity can be reduced by reducing the nitrate leaching by using nitrate-based fertilisers rather than ammonium based fertilisers but the removal of agricultural products as alkaline plant material will decrease soil pH over time.

Once the soil became acidic, the most practical way to ameliorate acidic soils is applying lime to neutralise soil acidity. Without on-going amelioration, agricultural soils can continue to acidify to the point where they become too expensive to recover.

If untreated, acidification is likely to affect a larger area of land than any other soil degradation problem (O’Connell et al., 1999)

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References

Bolan NS and Headley MJ (2003) Role of carbon, nitrogen and sulphur cycle in soil acidification in Z Regenal (ED) Handbook of Soil Acidity Marcel Dekker New York pp29-56

Department of Agriculture and Food (2013) Report card on sustianbel natural resource use in agriculture. Department of Agriculture and Food, Western Australia

Gazey C, Davies S and Master R (2014) Soil acidity: A guide for WA farmers and consultants. Second edition. Bulletin No.4858, Department of Agriculture and Food, Western Australia

O’Connell M, Bathgate AD and Glenn NA (1999). The Value of information from research to enhance testing or monitoring of soil acidity in Western Australia, Paper presented at the 43rd Annual Conference of the Australian Agricultural and Resource Economics Society, Christchurch, New Zealand, January 20 – 22, 1999.

Fry J (2015) Lime situation report 2015 South Coast NRM region. South Coast Natural Resource Management