Acidic soils occur naturally in some areas but human activities have accelerated soil acidification which is having negative consequences on agricultural production in many regions. Negative effects of acidification include changed soil biology, accelerated nutrient leaching, nutrient deficiencies and toxicities (Metcalfe and Bui 2017). Agricultural acidification is caused by adding acidifying fertilizers (such as some nitrogen fertilizers) and removing alkalinity (through removing plant products or leaching). Other localised acidification can be caused by sulfide oxidation, acid deposition from industrial pollutants, and land contamination. Because the addition and leaching of nitrogen fertilisers are associated with acidification, acidification risk increases when land use changes from low nitrogen inputs to high nitrogen inputs (Eugenio et al. 2018, VIC EPA 2018). An example of this land use change might be converting unimproved pasture into cropping, or cropping into intensive horticulture. Treatment of surface acidity is relatively simple and usually involves adding crushed lime sand, limestone, or dolomite; subsoil acidity is significantly more expensive to remediate. As always, prevention is generally less expensive than remediation and can be achieved to an extent by managing the type, rate, and timing of fertilizers and irrigation (WA EPA 2007).
Soil acidification affects about half of Australia’s agricultural soils (c. 50 million hectares), mostly in Western Australia and New South Wales (Metcalfe and Bui 2017). In the Western Australian wheatbelt alone, between 8 and 27 million hectares are estimated to have been affected by moderate to severe soil acidity in 2001; this area is likely to have expanded (WA EPA 2007). Acidification is accompanied by yield decreases; productivity losses in South Australia and Victoria due to acidity and acidification have been estimated at $88 and $470 million AUD per year, respectively (DEW 2018, VIC EPA 2018). Unfortunately, liming is expensive, and is not occurring at a rate that will prevent further acidification (Metcalfe and Bui 2017, VIC EPA 2018). However, precision agriculture provides an opportunity to prevent soil acidification through improved fertiliser regimes, and also to improve the management of acidity through variable rate liming (VIC EPA 2018). The lost opportunity in Australia associated with soil acidity for wheat production is estimated to be worth A$400 million per annum (Orton et al. 2018).
DEW. 2018. Tracking changes in South Australia’s environment – 41 trend and condition report cards. Government of South Australia Department of Environment and Water, Adelaide.
Eugenio, N. R., M. McLaughlin, and D. Pennock. 2018. Soil pollution – a hidden reality. Food and Agriculture Organization of the United Nations, Rome.
Metcalfe, D. J., and E. N. Bui. 2017. Australia state of the environment 2016: land. Australian Government Department of the Environment and Energy, Canberra.
Orton, T., T. Mallawaarachchi, M. Pringle, N. Menzies, R. Dalal, P. Kopittke, R. Searle, Z. Hochman, and Y. Dang. 2018. Quantifying the economic impact of soil constraints on Australian agriculture: A case‐study of wheat. Land Degradation and Development 29:3866-3875.
VIC EPA. 2018. Victorian State of the Environment 2018 scientific assessments. Authorised by the Commissioner for Environmental Sustainability, Melbourne.
WA EPA. 2007. State of the Environment Report: Western Australia 2007. Perth.
Soil Science Australia acknowledges the traditional owners of the land and pays its respects to their Elders, past, present and future.