Soil acidity and pH management for Central West districts


Over the past 2 decades a number of initiatives have identified soil acidity as a serious issue within the Central West of NSW. In early 2000; CWFS, GRDC, NSW Agriculture and the NSW State Government, via the Acid Soil Action program, identified that 57% of the red soils sampled within Central Western NSW had a pH of 5.0 or less. It is well documented that a soil pH of less than 5.5 will negatively impact upon non tolerant grain varieties and their associated yield.

Since the Acid Soil Action program, there has been an increase in continuous cropping and an associated increased usage of nitrogenous fertilisers within the grain growing areas of the southern GRDC region – of which the CWFS districts are a component – both factors have been demonstrated to increase the occurrence and rates of soil acidification.

Due to the negative impact of soil acidity upon Grain yield and the long term impacts upon the sustainability of the grains industry, GRDC have funded the next Soil Acidity awareness program with the Western Australian Department of Agriculture and Food (DAFWA), Southern Farming Systems (SFS), Primary Industries and Regions SA (PIRSA) and Central West Farming Systems (CWFS) partnering to address this issue in within the vulnerable soil types of their regions located within the Southern GRDC area.

Lime it or lose it

The most effective method of addressing soil acidity within a cropping system is the application of Lime.  Consequently this project is primarily extension based with the main focus being to raise the profile of the benefits of applying lime within at risk regions and soil types.

The CWFS component of the overall project is entitled: “Soil acidity and pH management for Central West farming districts” and is comprised of 6 main objectives:

  • In first instance sites within different at risk regions are to be resampled on an annual basis.  In 2014, 5 sites with a pH ranging from 4.8 to 5.2 within the 0-10cm section of the soil profile were resampled.  Initial results indicate an increase in acidification within the 0-10 depth with a pH of 4.2 encountered and the occourance of subsurface acidification.
  • A project steering committee has been established that is comprised of: agronomists, financial representatives, lime suppliers and landowners. This committee will guide the project and assist in the remediation of soil acidity within the CWFS region via their day to day contact with landholders and hands on knowledge of the issue.
  • Workshops targeted to growers within at risk regions will be delivered to raise the incidence of soil acidity within their own backyard. The workshops will cover what has been identified via the sampling program(s), causes of soil acidification, economic and environmental impacts of soil acidification and, best practise methods of addressing the issue via the application of Lime.
  • An advertising strategy targeted to at risk regions will be developed. It will identify the occurrence of soil acidification, causes, impacts and the benefits of Lime application. This will also include this web page as a component of the existing CWFS web site.  This will enable a lasting project legacy beyond the life of the project.
  • To further assist in leaving an ongoing project legacy a young soil acidity champion has been identified and will be trained in the causes, impacts and remediation of soil acidification.
  • On properties that have identified soil acidity issues, in cooperation with local land holders and Lime suppliers, trials will be established to demonstrate first hand to landholders the benefits of applying lime. These will also form a basis for further extension activities.

The success of: Soil acidity and pH management for Central West farming districts, will be gauged by a demonstrated increase in lime sales within the Central West Region of NSW.  To further raise the profile of the benefits of Lime within a cropping system, negotiations are currently underway between CWFS and the University of Southern Queensland with regards to a PhD project which will officially identify the potential benefits of applying Lime to sodic soils.  If successful this project will be conducted at the CWFS Condobolin irrigation research block.

liming in nsw

As seen in Table 1. Comparison of the pH levels for the historic sites demonstrate an increase in acidification overtime at all sites except for the Nyngan site where the area has been returned to permanent perrenial pasture.

Lime application

Table 2. Shows that in 2014 all of the “new” sites sampled, where lime has not been applied, pH levels are significant enough to impact upon plant growth with the occourance of subsurface acidification occouring at 2 out of 5 sites.

Soil pH change over time and the outcomes of a farmer led Lime trial, west of Condobolin NSW: an Overview.

In 2014, assessment of a previous soil pH monitoring site, sampled 14 years prior, and a farmer led  on-farm lime trial was conducted west of Condobolin NSW. In the on farm lime trial the farmer had independently applied 3 different rates of lime to an area that is subjected to dryland cropping and grazing. The impacts of the varying rates of Lime were assessed via: soil coring, in-crop wheat biomass assessment, tiller counts and volume of grain achieved at physical maturity.  Results showed that at the previous soil pH monitoring site, pH levels had decreased and subsurface soil acidification was occurring down to 30cm; and in the on farm lime trial the higher application rate of Lime achieved a higher pH in the top 10cm of the soil profile, prevented soil acidification from reaching lower sections of the soil profile and achieved notably higher plant biomass / number of tillers and volume of grain when compared to no Lime or reduced Lime applications.

Key Points:

  1. Visually the impacts of Lime may not be seen, but the benefits of Lime are evident when comparing Limed areas plant biomass and yield with that of un-Limed areas.
  2. Application of Lime has been shown to halt sub soil acidification which is costly to address and will impact upon future sustainability and productivity of an agricultural enterprise.
  3. Appropriate rates of Lime are shown to increases yield.


Results from the on-farm investigation demonstrate that where cropping activities occur within the Red Clay Loam soils of the Central West of NSW, soil acidification can increase in magnitude over time and that lime is required to ameliorate the effects of agricultural activities; i.e., product removal and nitrogenous fertilisers, which are known to cause soil acidification (Gazey & Davies, 2009). Results also demonstrate that without the application of Lime to a cropping environment, over time, acidification will move down through the soil profile causing sub soil acidification. Subsoil acidification further impacts upon plant growth (Jenson 2010) and associated yield as well as increasing the cost of acid soil rehabilitation (Gazey & Davies, 2009). The long term benefits of applying Lime within the Red Clay Loam soils of the Central West of NSW are clearly demonstrated via the on farm trial; ie,

  1. Where the maximum amount of Lime was applied; a “normal” increase in pH is viewed descending through the profile, the soil pH levels are such that plants can effectively access nutrients within the soil profile, which is reflected in the greater biomass /number of tillers and volume of grain.
  2. Where less Lime was applied pH levels are still appropriate for plant nutrient uptake however a reduced plant biomass /number of tillers and volume of grain was achieved when compared to the maximum volume of Lime.
  3. Where no Lime was applied, Sub surface acidification is occurring, and the lowest biomass /no of tillers and grain volume was observed.

This on farm Lime trial clearly shows that in a cropping environment, appropriate amounts of Lime are required to maintain soil pH. If Lime is not applied to address factors such as Nitrogenous fertiliser applications and product removal, acidification of the top section of the soil profile will occur. If Lime is not applied at this stage acidification will move down through the soil profile causing subsurface acidification.  As soils become more acidic nutrients required for plant growth become less available.

Appropriate rates of Lime applied to a cropping environment mean that the pH of the soil will allow plants to effectively access available nutrients which translate into plant growth, grain yield and maximising the value of fertiliser inputs.