Best practice liming demonstration to address subsoil acidity in northeast Victoria
Best practice liming demonstration to address subsoil acidity in northeast Victoria
Author: Jane McInnes (Riverine Plains Inc), Cassandra Schefe (AgriSci Pty Ltd) | Date: 31 Jul 2024
Take home messages
- Growers in the Riverine Plains should assume that their farm has some degree of subsurface acidification, unless soil test results prove otherwise.
- Lime incorporation is essential in broadacre cropping soils to optimise benefits.
- Growers should only incorporate lime to the depth that is suitable for that soil, as cultivating soil with other soil constraints (for example, sodicity, slaking) may result in poor seedbed preparation, emergence and trafficability.
Background
This GRDC project investment is designed to demonstrate different lime incorporation methods, evaluate the impact of different lime types and sources, as well as extend findings including comparisons of the economic and agronomic returns using the Acid Soils SA calculator tools. As part of the project, a replicated field trial was established to demonstrate best practice liming strategies, with unreplicated demonstration strips to monitor the impact of lime quality, over three years. Trials were established in the Rutherglen district and monitored for three years from 2022–2024. Treatments were initially established in 2022, however, yield data was not captured in that year due to waterlogging and slug damage as confounding variables.
Extension efforts continue to focus on raising grower awareness on the rate of acidification and pH stratification of soils in this region, including providing resources and tools available to assist management decisions. Soil analysis over time has been used to illustrate the impact of lime incorporation methods and the impact of lime source and quality on addressing stratified subsoil acidity. This is in addition to assessing the economic benefits of each treatment, and potential losses of production and decline in pH. A nil control — with no lime applied — was used to highlight the cost of complacency when addressing pH issues in both the short and long term. The data generated through this project is supporting growers to evaluate the most practical and economical methods to manage soil pH and paddock variability.
The objective of the project is for growers and advisers in northeast Victoria to have improved understanding of the state of topsoil and subsoil acidity, the limitations to crop profitability it causes, and finally, an improved knowledge of the agronomic and economic benefits of different lime sources, lime quality and incorporation methods.
Method
Treatments for the project were developed after consultation with a steering committee, made up of growers and researchers. These treatments are shown in Table 1.
Table 1: Best practice liming trial treatments.
Treatment # | Details |
---|---|
1 | Control – nil lime: nil incorporation |
2 | Nil lime, with shallow incorporation |
3 | Lime to target pH 5.2, incorporated by sowing |
4 | High rate of lime (to pH 5.8 [0-10cm]), incorporated by sowing |
5 | High rate of lime (to pH 5.8 [0-10cm]), incorporation by shallow discs to 10 cm depth |
6 | High rate of lime (to pH 5.8 [0-10cm]), deep incorporation (HORSCHE TIGER) to 20 cm depth, follow up with speed-tiller |
7 | High rate of lime (to pH 5.8 [0-20cm]), deep incorporation (HORSCHE TIGER) to 20 cm depth, follow up with speed-tiller DELUXE option |
An intense soil sampling regime was completed in February 2022 across each replicate. This provided baseline information to characterise the whole site (Table 2), as well as an understanding of current pH levels to ensure that the proposed incorporation methods were appropriate. Using this information, it was calculated that the rates of lime used in that year would be:
- lime required to achieve a target pH of 5.2: 1.2t/ha
- lime required to achieve a target pH of 5.8 (high rate): 5.0t/ha
- lime required to achieve a target pH of 5.8 to depth (high rate to depth): 8.5t/ha.
Table 2: Starting pH, Al and CEC values as measured from a transect sampling plan across the site.
Sample depth from (cm) | Sample depth to (cm) | pH (1:5 CaCl2) | CEC (cmol(+)/kg) | Aluminium saturation (%) |
---|---|---|---|---|
0 | 5 | 5.0 | 6.0 | <1.0 |
5 | 10 | 4.5 | 4.4 | 8.7 |
10 | 15 | 4.3 | 3.6 | 28.0 |
15 | 20 | 4.2 | 3.1 | 35.0 |
The application of lime to these levels was done using a range of surface and incorporation techniques, including a shallow incorporation by sowing, incorporation by discs to a depth of 10cm, and a deeper incorporation by a Horsch Tiger to 20cm depth. Fine lime was sourced from a manufacturer in Galong and coarser lime was sourced from a manufacturer in Mt Gambier.
Figure 1 shows the layout of the field-scale replicated trial, which includes a buffer sown to wheat, in 2023. The plots are 40m x 13m, with a 20m buffer in between. At one end of the replicated trial, strip trials were established to assess the impacts of two types of lime quality, granular (Mt Gambier lime) and fine (Galong lime), applied at 3t/ha and incorporated with sowing. The lime from Galong was very fine (neutralising value [NV] 97.6), with bulk density of 1.4, while the Mt Gambier lime (NV 99.6) was much coarser with a bulk density of 1.1.
Figure 1. Liming incorporation trial layout.
Lime was applied on 16 February 2022, with the incorporation completed on 17 February 2022. A Horsch Tiger was used for the deep incorporation, with calibration to ensure that the depth of the lime incorporation was kept above 20cm. The speed tiller was run over both incorporated treatments to ensure a smooth surface for ease of sowing. Once the treatments were completed, the host grower sowed and managed the trial site in line with the management practices used for the remainder of the paddock.
Soil sampling was conducted in January 2022, before the treatments were established, and resampled in January 2023 and 2024 to enable a direct comparison of liming treatments and their effect on soil properties over time. Soil samples were collected in increments of 0–5cm, 5–10cm, 10–15cm and 15–20cm, from 20 sampling locations across each plot using a hand corer, while the 20–30cm, 30–40cm and 40–50cm depth increments were collected from four GPS-located sampling locations in each plot using a hydraulic trailer-mounted corer.
Results and discussion
Soil pH
Results from the trial to date show that, when lime is applied without incorporation, it impacts pH levels at the surface and does not change the pH down through the soil profile due to its poor soil mobility. Figure 2a highlights that if no lime is applied further acidification through crop production will occur. Figure 3a indicates that if no lime is applied, there could be mixing of the current soil through the shallow incorporation to give an initial benefit but the acidification continues in year 2. Figures 4a and 5a show that incorporating lime by sowing can result in lime influencing pH in the top 5cm, with the rate of change depending on the quantity of lime applied. Incorporation of lime using shallow discs (Figure 6a), or deeper incorporation with the Horsch Tiger (Figures 7a and 8a) enables the lime to move further down the profile, to the depth of incorporation. By enabling the lime to move down the profile it is able to increase the soil pH. Shallow discs resulted in lime movement to 10cm, while the Horsch Tiger moved lime to 20cm.
Per cent aluminium
Aluminium is present in all soils as a key component of clay minerals. While aluminium is generally present in solid or complexed forms that do not influence plant growth, aluminium solubility increases as soil pH values decrease, resulting in higher concentrations of phytotoxic species of aluminium in the soil solution, which can impede root growth.
Figures 7b and 8b show that the deep incorporation of both rates of lime results in significant reductions in exchangeable aluminium down to 30cm.
Figure 2. Treatment 1 – nil lime, nil incorporation (a) pH, (b) per cent aluminium.
Figure 3. Treatment 2 – nil lime, shallow incorporation (a) pH, (b) per cent aluminium.
Figure 4. Treatment 3 – lime to target pH 5.2 (1.2t/ha), incorporated by sowing (a) pH, (b) per cent aluminium.
Figure 5. Treatment 4 – high rate of lime to pH 5.8 (5t/ha), incorporated by sowing (a) pH, (b) per cent aluminium.
Figure 6. Treatment 5 – high rate of lime to pH 5.8 (5t/ha), incorporated by shallow discs sowing (a) pH, (b) per cent aluminium.
Figure 7. Treatment 6 – high rate of lime to pH 5.8 (5 t/ha), deep incorporation sowing (a) pH, (b) per cent aluminium.
Figure 8. Treatment 7 – Deluxe option: high rate of lime to pH 5.8 at depth (8.5 t/ha), deep incorporation sowing (a) pH, (b) per cent aluminium.
While deep incorporation has shown positive results, it is important that growers only incorporate lime to the depth that is suitable for that soil, as cultivating soil with other soil constraints (for example, sodicity, slaking) may result in poor seedbed preparation, emergence and trafficability.
For example, if you can only cultivate to a depth of 10cm, load up that zone with adequate lime for full amelioration of the target depth, so that there is sufficient lime to continue moving to depth over time.
Acknowledgements
The research undertaken as part of this project is made possible by the significant contributions of growers through both trial cooperation and the support of the GRDC, and the authors would like to thank them for their continued support. The authors would like to thank the Spence family for hosting the site and AgriSci for their continued support, data collection and maintenance of the site.
Contact details
Jane McInnes
9/95–103 Melbourne Street, Mulwala NSW 2647
0418 563 015
jane@riverineplains.org.au
@riverine_plains
GRDC Project Code: RPI2104-001SAX,