Soils Program

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Soil acidity affects more than 50% of intensively used agricultural land in NSW and approximately 23% in Victoria, and is especially prevalent in the higher rainfall areas in our region. If we do not address acid soils now, further acidification will threaten future agricultural production.

Recent research on soils in the NSW Southern Slopes suggests that in most cases, current rates of lime application are not addressing the current soil acidification rate. An effective liming program should aim to increase soil pH (CaCl2) to a target of 5.5 in the top 10 cm, not 5.0 as has been the current practice. This will provide sufficient lime to raise pH in the surface soil and allow for excess lime to leach into deeper subsurface layers (5 – 20 cm) and slowly increase pH at depth.

Lime that is top-dressed moves very slowly into the subsurface layers, depending on soil type, rainfall and lime application rate. It is known that effective incorporation of the lime after spreading ‘speeds up’ the reaction of lime with the soil, to the depth of cultivation.

HLN in conjunction with NSW DPI have set up two new trial sites that will be looking at these questions – different liming rates, top-dressing lime vs incorporating and the effects on crop and pasture growth. Another issue being looked at is pH stratification – acidic layers in the soil that may be impacting crop and pasture growth but are not being detected by traditional soil tests that bulks samples into 10 cm intervals. A background on each of the projects is provided below.

‘Future Soils’  2020 – 2022

The ‘Future Soils’ project is funded by the Australian Government’s National Landcare Program to improve on-farm management of acid soils. The project is managed by FarmLink and is a collaboration between NSW DPI, the Australian National University, FarmLink, Holbrook Landcare Network, Central West Farming Systems, K-Line Ag and Westlime.
HLN is hosting one of the five trial sites for the 3-year project, a replicated farm-scale site at Burrumbuttock. The trial consists of 7 treatments investigating 4 different liming rates of 0.5 t/ha, 1 t/ha, 2.5 t/ha and the ‘one-in-a-generation’ 6 t/ha, as well as the effect of lime incorporation compared to surface applied. A total of 28 plots (7 treatments replicated 4 times), 70 m × 9 m in size, were marked out in early 2020 and NSW DPI used their direct drop spreader to apply the lime on the plots. Canola was sown at the site in mid-April 2020.

‘New approaches to tackling soil acidity in perennial pasture systems’  2019 – 2021

The ‘Tackling Soil Acidity’ project, is a 2-year project funded by the Australian Government’s National Landcare Program, with contributions from HLN, NSW DPI and the Grasslands Society of NSW Inc.

The main components of this project will:

  1. Introduce new soil sampling practices to detect and monitor subsurface acidity.
  2. Use large-scale acid soil management sites to test a combination of different lime rates, with and without incorporation, and investigate the impact of different soil pH targets on ameliorating subsurface acidity in the short term. In the long term we aim to attract future funding to monitor pasture response to the range of pH profiles created by the various treatments; and
  3. Survey perennial pasture paddocks to identify the current status of soil pH in layers from depths of 0-30 cm. Geolocated sites to be established as long-term monitor sites to track acidification over time.

Soil sampling to detect and accurately measure subsurface acidity

Accurate soil sampling is an investment in time and money. The following videos provide some tips on how to get the most from time spent in the paddock.

Is subsurface acidity an issue for you? This video A rapid check for subsurface acidity in the field shows how a Digstick and field pH kit can give a quick indication of the pH profile.

Accurate soil sampling for subsurface acidity. This video shows why soil samples collected at 5 cm intervals to a depth of at least 20 cm are necessary to detect subsurface acidity. Soil tests collected from traditional sampling depths of 0-10 cm and 10-20 cm do not detect acidic layers that commonly occur at 5-15 or 20 cm. Knowing the variation in pH in the 0-20cm (also known as pH stratification) will help guide species selection and liming programs.

Acid soil management site

HLN and NSW DPI are managing a trial site located in a paddock on ‘Boorook’, near Morven. This site was selected for this experiment as it has no previous liming history and has uniform soils across the paddock that are severely acidic ( pHCa < 4.5; Exch Al. > 20%) to depth.

The trial site was established, and lime spread in October 2019. The trial consists of 7 treatments investigating lime rates and the effect of lime incorporation (Inc) to a depth of about 10 cm with disc harrows, compared to surface applied (SA). The treatments were decided by the project steering committee made up of local producers, advisors, LLS representatives and the project research team. The amount of lime applied, was determined by the starting pH and ECEC and the target pH. The details for each treatment are below:

(i) Nil lime (Control)
(ii) Treatments 2 (SA) and 3 (Inc); 4t/ha lime targeting  pHCa > 5.5 in the 0-10 cm depth;
(iii) Treatments 4 (SA) and 5 (Inc); 3t/ha lime targeting  pHCa > 5.2 in the 0-10 cm depth (i.e. approximating current industry recommendations);
(iv) Treatments 6 (SA); 2 t/ha lime aimed at increasing  pHCa of the surface 0-5 cm layer > 5.5; and
(v) Treatments 7(Inc); a ‘once-in-a-generation’ application of 6t/ha lime targeting a  pHCa > 6.0

A canola hybrid was sown at the site in mid-March 2020, and a phalaris based pasture is planned to be sown down in 2021.

In April this year NSW DPI and HLN staff visited the site to look at the establishment and development of canola and the impact different lime treatments have had on the plants. The standout response was increased root density and top growth in the lime treatments, and particularly where lime was incorporated, as can be seen in the photograph.

Here is a video of Helen Burns (NSW DPI) in the paddock showing plant examples from the different treatments displaying various root development and manganese toxicity symptoms (mottled leaves).


‘Soil Monitoring of Acid Soils’  2017 – 2020

Project Background

The aim of the ‘Soil Monitoring of Acid Soils’ project, funded by Murray Local Land Services, was to monitor changes in soil pH and fertility over time at selected sites across the Murray region and consider the management practices that have influenced these changes. The project was a follow on from the 2017 ‘Sub Clover Nodule Health Project’ that collected baseline soil data and assessed the nodulation status of pasture legumes from 40 sites sampled in September 2017. In March 2020, 31 of these sites were resampled to monitor changes in soil properties. Paddock management information such as production outputs and liming and fertiliser inputs was collected from landholders to gauge the effect that these factors may have on soil pH and fertility status. The nodulation status of legumes was not assessed in this project, due to the unfavourable seasonal conditions in 2019.

Key Findings

  • In most cases, current liming practices are not addressing the current acidification rate.
  • 45% of paddocks have severely acidic (pHCa < 4.5) subsurface layers (5 – 20 cm). This has increased from 26% of the same 31 sites in 2017.
  • Only 7% of paddocks have pHCa >5.0 in the subsurface layers (5 – 20 cm). This has declined from 16% of the same sites in 2017.
  • 86% of paddocks that have been limed in the last 5 years have  pHCa levels above 5.0 in the surface but are moderately (pHCa5-5.0) to severely acidic (pHCa <4.5) in the subsurface layers below 5 cm.
  • Recent research on soils on the NSW Southern Slopes suggest acidic surface and subsurface soils should be limed to increase pHCa to a target of 5.5 of the surface 0 – 10 cm layer. This will provide sufficient lime to raise pH in the surface soil and allow for excess lime to leach into deeper subsurface layers and slowly increase pH at depth.
  • It is expected that sub clover nodulation health is also declining with acidifying soils.
  • Soil phosphorus levels were above critical values (>30 mg/kg P) in 74% of the paddocks, an increase of 3% since 2017 sampling. The majority of these paddocks have received between 100 and 200 kg/ha of super, MAP, or DAP every year.
  • Organic carbon (OC) for all sites averaged 2.3% and ranged between 1.4% and 3.7%. Average OC was 1.8% in the <600 mm rainfall zone, 2.4% in the 600 – 800 mm zone and 3.2% in the >800 mm zone. Compared to 2017, OC has decreased slightly in the <600 mm rainfall zone from 2.0% to 1.8%, and increased in the higher rainfall zones, although not significantly.
  • Soil testing should be conducted around the same time of year in order to monitor changes in soil properties. This is necessary to minimise the natural variability that can occur between seasons in soil pH and exchangeable aluminium values.
  • When monitoring trends in soil pH, sampling intervals of 5 cm to a depth of 20 cm are recommended. NSW DPI recommend using a 25 mm diam. core tube to collect the core and cut and bulk the core into 5cm intervals. A video providing detailed instructions on accurate soil sampling can be found above.
  • Regular soil testing is important to make sure inputs are matched to requirements and that investment in one type of input is not wasted because the other is still a constraint on production.

More information: contact Nick at the HLN Office on 02 6036 3181

‘Subsoil Acidity’  2016 – 2020

    1. Update June 2020: The final season of crop was harvested at the end of last year and final soil sampling was conducted in March 2020. An analysis of the data is currently underway and the final report is expected to be released towards the end of the year.
    2. Update June 2018:  NSW DPI has released a number of case studies on Managing Soil Acidity. To view all case studies within Soil Acidity project click:   or to see the case study for the Holbrook trial go to Issue 08: Amelioration of subsoil acidity using inorganic amendments
    3. Subsoil acidity is a major constraint to crop productivity in the high rainfall zone (500-800 mm) of south-eastern Australia. Soil acidification is accelerated by: nitrate leaching under certain crop rotations, the use of ammonium-based fertilisers, and the regular removal of plant products, such as grain or hay. The major constraint to plant production on acid soils is aluminium toxicity which inhibits root growth. Smaller root systems limit nutrient and water uptake and increase plant vulnerability. HLN’s Subsoil Acidity project is now in its final year. Initially the trial sites were established with varying treatments, including deep ripping lime or lucerne pellets precisely to the 10-30cm zone, deep ripping alone, and surface-applied lime. Soils were sampled prior to site establishment and will be sampled again after three years of crops. HLN staff have just completed the crop sampling process of the 12 plots on both trial sites. Visual results showed some clear differences in crop growth across the different treatments. A summary of this projects progression will be available shortly via the HLN website. A big thank you goes to Andrew Landale and Tony Geddes for their support with all aspects of the trial.
    4. HLN will be conducting two on-farm demonstration experiments over the next four cropping seasons to explore methods of managing subsoil acidity. The ultimate goal is to ensure the research results are delivered to farmers to help prevent or ameliorate the risk of significant yield loss due to subsoil acidity. HLN is one of 4 cropping groups that will conduct the trials as part of a GRDC project – Innovative approaches to managing subsoil acidity in the southern grain region. Two sites will be selected in the Holbrook area on highly acidic soils (pH 4.0-4.5 at 10-20 cm) and demonstration trials will be established in consecutive years to offset seasonal effects. It is envisaged that treatments will include surface liming, deep placement of lime, and subsoil manuring with surface liming, but other amendments may also be investigated.The first experiment will commence in the 2016 growing season with the second beginning in the following year. Both sites will be actively managed for three years, with the trials finishing in 2019. A field day will be held each year to promote discussion about the effectiveness of the treatments, methods and products used.
    5. Subsoil acidity project update 8/3/2016: After an intensive search for sites with the required pH and aluminium levels – that would also be cropped for at least three years – the first of these trials, located at ‘Teripta’, has now been established.NSW DPI technical staff and researchers spent almost a week on-site with their purpose-built deep ripper, which was able to rip and apply lime or lucerne pellets precisely to the 10-30cm zone. Other treatments are deep ripping alone, and surface-applied lime. Soils were sampled prior to site establishment and will be sampled again after three years of crops.The trial site will be sown on the next rain, and the plots sampled throughout the growing season to monitor the treatment effects. Another similar trial will be established in the district next year, and will be monitored for a further three years.The team working on the subsoil acidity project met in Wagga recently to update progress from all aspects of the project. Of interest are some early results from glasshouse trials at La Trobe Uni, which have found poultry litter, sheep manure, mature dairy compost, biosolids and poultry manure biochar consistently performed best when looking at wheat shoot biomass. The detoxification of aluminium in the soil was not exclusively due to pH increases, but there are other mechanisms at work with some of these organic amendments.In another glasshouse trial, results are showing that the placement depth of the amendment is important. Higher rates of the organic amendment at the top of the toxic layers is best, and essential, and root growth is stimulated below the amended layer. Again, pH and Al levels are not telling the whole story of the mechanisms involved.These options to ameliorate subsoil acidity still need to be thoroughly investigated at farm scale, economically and practically, but are giving some promising directions for that research.
    6. Factsheet 1
    7. Factsheet 2
    8. Subsoil Acidity Project trial sites update January 2017
      The first cropping season for the trial site at ‘Teripta’ is complete, and a big thank you goes to Andrew Landale for his support and willingness to help with all aspects of the trial. Early visual results showed some clear differences in crop growth across the different treatments, before intermittent waterlogging of the site occurred. The wet season meant there was some doubt about getting results from the trial, but we managed to collect all the relevant samples, and the canola was harvested at the end of December. Thanks also to Lachlan Casey and Dermott McMannus for their hard work in harvesting and weighing the yield for each plot.
      The second trial site is in the process of being established at ‘Innisfail’, with soil sampling starting next week. Treatments will then be applied before sowing. Thanks to Stephen Bunyan for providing the site. Hopefully we will have a better season and get some good results from the two concurrent Holbrook Landcare trials this year.

HLN have been offering the Soil Testing Program in the area since 2011. The program allows landholders in the South West Slopes & Upper Murray regions of NSW to access subsidised or discounted soil tests. Soil testing is an important tool in helping farmers make informed decisions to improve soil fertility in both grazing and cropping enterprises. The Soil Testing Program can assist you in better understanding your soil fertility; how to measure it, why it is important, interpreting the results and developing strategies for managing or improving it. 

To participate in the program or for more information click on the below links.


As part of the program, workshops are held in various locations to help you interpret your soil test results, develop management strategies and compare them to the district soil test results.

Information presented at previous workshops: 

For many farming enterprises, the application of phosphorus fertiliser is one of the largest annual expenses. HLN, as part of the Carbon Farming and our Business project, has developed a phosphorus budgeting tool which can be used in conjunction with soil testing. An annual fertiliser plan and budget can be developed by using this easy to use, excel-based tool.

In this new project HLN propose to develop benchmark and extension information on key quality and health for our local soils which will contribute to our capacity to influence managers of permanent pastures and achieve better outcomes for groundcover, soil health and productivity. A soil biology snapshot will be established for 5 of the region’s main soil types across a seasonal gradient and use our soils database of 1000 soil tests over the past 4 years to create a picture of soil health for 4 different farming systems across the spectrum of management styles. There will be more to come on this project in the future.

For information on past soils projects go to our ‘Resources’ page.