Key messages
- Riverine Plains and GRDC trials at Lilliput showed that applying lime, followed by incorporation, increased subsurface pH and reduced aluminium availability
- Incremental soil testing helps identify where and how severe acidity is, allowing the right rate of lime to be calculated
- While deep incorporation has shown positive results, it’s important to only incorporate lime to a suitable depth for that soil
- Good seasons can mask the effects of soil acidity
Soil acidity is a widespread production constraint in the Riverine Plains, robbing paddocks of productivity and making life tough for sensitive crops like pulses.
But just applying lime on the surface doesn’t always fix the problem, especially when acidity is sitting deeper down the profile. Soil also re-acidifies over time, which means that lime needs to be reapplied at intervals, raising questions about lime quality, rate and how to get the most bang for your liming buck.
That’s why Riverine Plains, through an investment of the Grains Research and Development Corporation (GRDC), ran a three-year best practice liming trial at Lilliput, near Rutherglen. The idea was to put some hard numbers around different rates, types, and ways of incorporating lime, to see what really works in our soils.
With liming season now upon us, we are sharing a snapshot of this research, to help inform your decisions this year and beyond.
Our replicated liming and incorporation trial was established in 2022. After three years of soil testing and harvest data, the trials gave us some clear learnings.
Testing in 10 cm increments shows where acidity sits in the profile, so you can match lime rates and incorporation strategy to the problem. It can also show the presence of other constraints at depth. For example, our trial site had a sodic later below 20 cm, so a maximum incorporation depth of 15 cm was set, to avoid bringing up sodic soil into the surface layer.
Lime moves very slowly down the soil profile, so just spreading lime on top — without incorporation — often only changes the pH value on the surface. In this trial, incorporating lime by sowing increased pH in the top five cm, with the rate of increase depending on the amount of lime applied.
A target soil pH of 5.8 is now recommended to optimise growth across all varieties and provide enough alkali to move down into the subsurface.
For this soil, we calculated that 5 t/ha lime was required to increase pH to 5.8 across the 0–10cm depth. When this rate of lime was applied and then incorporated with shallow discs, it improved pH and reduced aluminium availability through the 0–10 cm zone, to the depth of incorporation.
Incorporating with discs or deeper cultivation with a Horsch Tiger aimed to move 5 t/ha lime to a depth of 15–20 cm, while avoiding bringing up soil from the sodic layer beneath 20 cm. The results showed that the Horsch Tiger was successful in moving the lime to the depth of incorporation (15cm) and in reducing aluminium saturation to that depth.
When we targeted an overall increase in pH to 5.8 to a depth of 0–20cm, we calculated that 8.5 t/ha lime was required in this soil, incorporated to a depth of 15cm. This “Deluxe” option, combining high rates of lime and deep incorporation, was able to completely ameliorate soil acidity and decrease aluminium below the toxicity threshold.
A side-by-side demonstration of coarse lime and fine lime showed both raised pH at an application rate of 3 t/ha, compared to a nil application rate. The real driver was how much was put on, not the fineness of the product.
Interestingly, yields didn’t change much in 2023 and 2024 across treatments, including the nil lime control. Both were good seasons for growing wheat, with ample stored soil moisture, which reduced plant stress and likely masked the effects of acidic layers.
Yields are often poorer on acidic soils in drier years, due to impaired root growth as a result aluminium toxicity, with pulses being more sensitive than cereals.
In 2024, higher lime rates and deep incorporation also lifted grain protein, likely from better nitrogen use efficiency.
Lime is expensive, especially once spreading and incorporation are added in. In this trial, costs ranged from about $380/ha (5 t/ha incorporated at sowing) up to nearly $800/ha (8.5 t/ha with deep incorporation).
Because of this, it helps to think of lime as an investment, with the upfront spend in year offset by the payback over many years. Break-even depends on yield response, but the bigger issue is the cost of doing nothing: worsening acidity, limiting root systems, and declining yields.
Soil test in layers: Incremental testing is the only way to identify the location and severity of soil acidity, and other constraints
Target pH 5.8: Work out lime rates that can help reach that level
Incorporate to the right depth: If you can only safely work 10 cm, put enough lime in that zone so it can move down over time
Don’t overthink lime quality: Both fine and coarse limes work, as long as the rate is right
Think long term. Lime may be expensive in year one, but it supports long-term productivity
The Riverine Plains Best practice liming to address sub-soil acidity project has shown how lime incorporation can ameliorate acid soils to a greater depth. It’s also highlighted how incremental soil tests can identify the location and severity of acid layers, which can then be used to calculate an effective application rate for your soil.
While yield results didn’t differ dramatically over the course of the trial, the soil chemistry results tell the real story. And in tougher seasons, or with sensitive crops, those changes could be the difference between breaking even and going backwards.
This article is based on a feature from our 2025 Trial Book and you can explore the full article and insights here: Best practice liming in north east Victoria - final trial results
To learn more, please contact Riverine Plains Head of Farming Systems, Jane McInnes at jane@riverineplains.org.au.
This project is an investment by the GRDC, led by Riverine Plains. A special thanks to the Spence family for hosting the trial site and to Dr. Cassandra Schefe, AgriSci.