Soil acidification is an ongoing and unavoidable result of productive agriculture. The main practices that cause soil acidification include removing harvested products (Figure 1) and leaching of nitrate from soil. Because soil acidification is an ongoing result of farming, management also needs to be ongoing.
Farmers in Western Australia are increasing their use of lime (Figure 2) and appropriate soil sampling to identify and prioritise lime application. For example, a survey was conducted of nearly 400 grain growers from across the WA wheatbelt who indicated that the most common rates of application of lime would increase from 1–1.5 t/ha to 1.5–2 t/ha. Farmers also indicated that they intended to increase their testing of soil acidity in the subsurface layers. Farmers in Western Australia are also using more targeted applications of lime. Over 2010 to 2012, 75% of farmers applied lime at a single rate across paddocks. This method results in most soils receiving either too little or too much lime and not enough lime use overall. In the future, 50% of farmers intend to lime according to management areas or ‘patch out’ lime based on soil sampling results.
Figure 1: Hay production (especially legume hay) in one of the most acidifying practises.
Despite higher applications of lime, the evidence clearly shows that soil pH in many areas of the south-west agricultural region is continuing to decline. Currently, more than 70% of soil samples from the 0–10 cm layer have pHCa below the minimum appropriate level of 5.5. In the 10–20 cm and 20–30 cm layers of soil, almost 50% of soil samples have pHCa below the minimum appropriate level of 4.8. Soil acidity continues to be a major constraint to yield in Western Australia. Soil acidity costs WA agriculture about $500 million per annum in lost productivity (Herbert 2009). Without appropriate management, soil acidity will continue to prevent farmers from achieving their rain limited yield potential.
Figure 2: Agricultural lime sales show that although lime use is increasing, it is only 60% of the estimated annual requirement for the next 10 years (Source: Lime WA Inc.)
To manage soil acidification in Western Australia, more lime must be applied to agricultural soils. The most effective method is to apply the right rate of lime in the right place at the right time. This will use resources most effectively and provide the best returns on investment.
Soil testing has a vital role in the management of soil acidity (Figure 3). It is important that decisions on where and when to apply lime and how much lime to apply are based on objective measures of soil acidity. While it is possible to estimate maintenance liming rates based on farm inputs and outputs, the most direct method, and the only way to measure existing acidity, is to regularly test the surface and subsurface soil layers.
Figure 3: Professional soil testing that geo-locates samples allows accurate repeat sampling and monitoring of soil pH. Photo: Precision SoilTech
Liming can increase grain yield when soil pH is below recommended targets and when soil pH is one of the factors constraining yield (Table 1). The Department of Agriculture and Food, Western Australia and CSIRO investigated how liming affected yield in 69 lime trials from across the WA wheatbelt. On average, applying lime increased yield by 0.2 t/ha or 10%. This result is similar to what has been found in most other trials around Australia.
Table 1: 2013 grain yield response to 1994 lime treatments (subsequently each treatment received 4 t/ha of farmer-applied lime) at a trial near Mingenew, WA.
1994 Lime Treatment (t/ha)
2013 Wheat Grain Yield (t/ha)
Different Letters indicate a significant difference
However, the yield increases from liming may be even higher than this. When trials have included ripping or tillage, increases in yield were even greater. Also, it takes a few years for lime to react with the soil and increase the soil pH. If yield was calculated starting from the third harvest after lime was applied, the average yield increase was 0.25 t/ha or 16%. Yield and yield gains from liming will depend on the relationship between paddock yield and yield potential. If the paddock yield is low relative to the yield potential there is likely to be additional constraints present and there may be little gain from liming. Also, if the paddock yield is already close to potential pH is not likely to be a constraint and there may also be little immediate gain from liming. However maintenance liming will be required to counter ongoing acidification and maintain the productivity of the paddock.
Gazey C, Davies S and Master R (2014) Soil acidity: a guide for WA farmers and consultant, second edition, Bulletin 4858,Department of Agriculture and Food, Western Australia.
Gazey C, Oliver Y, Fisher J, Andrew J and Carr S (2014) ‘20 years of soil acidity R, D and E in Western Australia—what have we learnt?’ 2014 Perth Crop Updates http://www.giwa.org.au/2014-crop-updates
Herbert A (2009) ‘Opportunity cost of land degradation hazard in the south-west agricultural region’, Resource Management Technical Report 349, Department of Agriculture and Food, Western Australia.
Authors: Chris Gazey (Department of Agriculture and Food, Western Australia) and Jennifer Carson (Ghost Media).
This soilquality.org.au fact-sheet has been funded by the Healthy Soils for Sustainable Farms programme, an initiative of the Australian Government’s Natural Heritage Trust in partnership with the GRDC, and the WA NRM regions of Avon Catchment Council and South Coast NRM, through National Action Plan for Salinity and Water Quality and National Landcare Programme investments of the WA and Australian Governments.
The Chief Executive Officer of the Department of Agriculture and Food, The State of Western Australia and The University of Western Australia accept no liability whatsoever by reason of negligence or otherwise arising from the use or release of this information or any part of it.whatsoever by reason of negligence or otherwise arising from the use or release of this information or any part of it.