Best practice liming

WHY IS THIS PROJECT IMPORTANT

Acid soils have long been a major constraint to crop and pasture production in northeast Victoria. The reacidification of previously limed soils and pH stratification are also becoming increasingly important issues for the region’s grain farmers.

This project aims to increase awareness of the speed of acidification and stratification of soils in the region, as well as the tools available to assist management decisions.

In short: This project addresses acid soil challenges in northeast Victoria by showcasing different liming practices in a field trial. It compares various treatments to inform economic and agronomic decisions, aiming to boost awareness and management strategies for improved soil health and crop productivity.

Background

Acidity levels in topsoil and sub-surface layers are increasing across the southern region of Australia and are a key constraint to productivity.

Applying lime to address increasing acidity is often the first input to be dropped when cash flow is limited due to its high cost. Additionally, the development of acidity can be masked where an acid throttle (a layer of low pH that restricts movement of nutrients and roots past it) exists in a stratified layer. This is often overlooked in lab analysis of 0-10 cm mixed soil samples. Often growers do not recognise the gradual decline in fertility and do not apply lime until the problem is already established.

With the low solubility of lime and its relative immobility, top-dressed lime can take ten or more years to significantly increase subsoil pH below 10 cm. Soils that have not been adequately maintained with lime applications, to counter the increasing rate of acidification, need a management solution to increase subsoil pH, as well as having a faster return on investment and increase in crop productivity.

The placement of the lime in the soil plays a significant role in the lime’s ability to neutralise acidity when it exists at depth due to the need to establish contact for the acid base reaction to occur. The quality of the lime is another factor contributing to its effectiveness in neutralising soil acidity, specifically its neutralising value.

Effective Neutralising Value (ENV) describes a chemical property of the lime based on its calcium carbonate equivalence (CCE) to neutralise acid, which can vary greatly between lime sources.  The lime’s fineness also has a significant impact on its ability to neutralise acid, with finer products having a higher surface area, and therefore greater contact with soil particles to improve its efficacy. A higher ENV  lime is generally more expensive, so ensuring maximum value from higher ENV lime through effective placement in the soils is of great significance to farmers.

Project focus

The project involves the establishment of a replicated lime treatment field trial at Lilliput, Victoria, to demonstrate best practice liming practices and how the incorporation of top-dressed lime can improve its distribution down the soil profile and lessen the impacts of soil acidity on subsequent crops.

The trial was established in early 2022 and is comparing the performance of subsequent crops under different treatments. The demonstration aims to show the difference between coarse and fine limes, as well as the impact of incorporation methods. Treatments include:

• Nil-lime
• Nil-lime with incorporation only
• Lime applied at 1.2t/ha
• Lime applied at 5t/ha deep incorporated
• Lime applied at 5t/ha shallow incorporation
• Lime applied at 8.5t/ha with deep incorporation (NB deep-incorporation was done using a Horsch Tiger and shallow-incorporation with a speed tiller).

These results are being used to inform an economic analysis of the treatment options, while intensive soil sampling will also help to understand differences in nutrient availability, pH and soil organic carbon between treatments.

The project also involves a demonstration trial of the impact of different lime types and sources, including an elemental sulphur treatment to accelerate acidification and give an indication of the future effects if lime was not applied.

Project outcomes

The latest results from the Best practice liming trials were published in Research for the Riverine Plains, 2024

Best practice liming demonstration to address soil acidity in north east Victoria

Key messages

• Lime incorporation is essential in broadacre cropping soils to optimise benefits
• Farmers in the Riverine Plains should assume that their farm has some degree of subsurface acidification, unless soil test results prove otherwise
• To-date, results from the Best-practice liming trial show that when lime is applied without incorporation, it only impacts pH levels at the surface and does not flow down through the soil profile
• Incorporating lime by sowing changed pH in the top 5cm, with the rate of change depending on the quantity of lime applied
• Shallow discs moved the lime to 15cm, while the Horsch Tiger moved lime to 20cm as targeted

• Farmers should only incorporate lime to the depth that is suitable for that soil, as other soil constraints (eg sodicity, slaking), seedbed preparation, emergence and trafficability can come into play.

Detailed results from this trial were published in Research for the Riverine Plains, 2024. Read the full article.

Best practice liming to address sub-soil acidity

Results from the project's 2022 trials were presented in Research for the Riverine Plains, 2023.

Key messages were that:

• Paddocks with a history of no-till management (cropping and pasture) may have highly stratified pH values in the top 20cm. This means accurate testing for soil acidity may require sampling at 5cm increments, rather than the traditional 10cm increments.
• Not all lime has the same Calcium Carbonate Equivalence (CCE) value and therefore they have different capacity to neutralise acidic soils, get yours tested.

The trial aimed to demonstrate best practice liming strategies and a field demonstration of the impacts of lime quality. However Slugs caused significant damage to the whole paddock in 2022, despite the site being baited twice. Anecdotally, it appeared that plots that had incorporation and lime treatments were less affected by slug damage, and damage was higher where lime wasn’t incorporated. This however, was not able to be quantified. 

The region also experienced a large rainfall event in January, with the site receiving around 150 mm. There was a total of 1150mm for the year and 538mm growing season rainfall, May-Oct. October had a large rainfall event, which caused the canola to lodge in patches, or die. Due to the condition of the crop, harvest was not able to be carried out by a plot header for the trial site, which disappointingly, resulted in no trial yield data (Figure 4). Despite the crop being black and on the ground, the host farmer harvested the site with the remainder of the paddock.

Additional information

Riverine Plains hosted a paddock walk shortly after soil amelioration had been completed. A dig stick and visual observation were used to confirm that the incorporated lime had moved to the required depths.

The areas eaten by slugs were re-sown in an attempt to improve crop cover and trial uniformity, mimicking local grower practice for patchy establishment/slug damage. Re-sown sections were able to compensate for the poor establishment later in the season.

Due to the site experiencing extensive waterlogging there were concerns waterlogging effects would confound trial results, and that the effects from amelioration treatments may not be able to be inferred from yield and soil test results. However, preliminary analysis of the soil test results in 2023,  indicated treatment effects were present, despite waterlogging of the site.

A detailed method, results and discussion was presented in Research for the Riverine Plains, 2023. Read the full article.