Take home messages

• After 3 seasons, a positive economic response is yet to be measured from applying lime and incorporating it effectively
• Limed treatments however are starting to show increased yield compared to the control, which is slowly recovering the cost of lime application and incorporation
• Cultivation of this long term CTF/no tilled paddock has increased both grain yield and economic performance compared to the control
• The addition of lime at 3t/ha has resulted in target soil pH levels to be achieved, but only with sufficient cultivation to the target depth. There was no advantage of fully mixing the soil and lime with a rotary hoe compared to chisel ploughing and offset discing.
• The addition of lime and cultivation has increased soil Colwell P at the surface, and increased the soils CEC to the depth of the cultivation
• The addition of micronutrients (Zn, Cu and Mo) is showing small positive biomass and yield benefits, but only in the limed treatments. Yield was reduced when micronutrients were applied without lime.

Background

A trial was established in May 2022 at the Ag Grow Agronomy research farm ‘Ridge Top’ near Beelbangera, 16km NE of Griffith in southern New South Wales. The site chosen was based on prior knowledge of historical soil tests, as well as the soil type being locally relevant in the region.

The trial was set up to measure:

1. The efficacy of applied lime on grain yield and profitability
2. Differences between incorporation methods
3. Differences between incorporation depths
4. Impact on phosphorous (P) and micronutrient uptake efficiency following lime application.

Comprehensive soil tests, including soil organic carbon, NO3, NH4, Colwell P, pH, EC, ESP, and trace elements, were undertaken at the trial site in April 2022.

The pH (CaCl₂) of the site was:

• 0–5cm          5.4
• 5–10cm        4.4
• 10–15cm      4.5
• 15–20cm      5.2

The trial was statistically designed and consisted of 4 replications with treatments including:

• 3 lime rates
  • 0 t/ha lime
  • 3 t/ha lime
  • 6 t/ha lime
• 5 cultivation treatments
  • nil cultivation (sowing only) (except the 6 t/ha lime)
  • 10 cm chisel + offset
  • 20 cm chisel + offset
  • 20 cm chisel + offset twice
  • rotary hoe
• 4 phosphorus treatments
  • Plus P
  • Nil P
  • Plus P + Micro
  • Nil P + Micro

Crop rotation has been wheat (2022), followed by canola (2023), then wheat in 2024. Lentils are planned for 2025.

All appropriate agronomic management and economic analysis was performed the same as the commercial paddock.

Impact of treatments on soil tests performed 12 months afterwards

There were no significant differences in the soil pH of treatments that received no lime, regardless of cultivation treatments (red lines and symbols, Figure 1).

The 6 t/ha lime treatments increased soil pH relative to the control to 20cm. Incorporation method had no significant effect on pH profile when lime was applied at 6 t/ha. Note there was no nil cultivation in the 6 t/ha lime treatments.

Cultivation increased the depth of pH change when lime was applied at 3 t/ha. The 10 cm chisel followed by offset disc significantly increased pH in the 5–10 cm layer relative to the control and lime at 3 t/ha that was incorporated by sowing.

Figure 1. Impact of treatments on soil pH (CaCl2) sampled in 2023. Horizontal bars indicate least significant difference (p=0.05), *** indicates significant main effect for lime addition where no individual treatment differences occurred, ns denotes no significant difference.

There were no significant differences in the cation exchange capacity (CEC) of treatments that received no lime, regardless of cultivation treatments (red lines and symbols Figure 2).

The 6t lime/ha treatments increased CEC to a depth of 15cm relative to the un-limed treatments receiving the same cultivation.

Cultivation increased the depth of CEC change when lime was applied at 3 t/ha. The 10 cm chisel followed by offset disc significantly increased CEC in the 5–10 cm layer relative to the No lime control and 3 t/ha lime that was incorporated by sowing.

The increases in CEC match the increases in soil pH due to treatment.

Figure 2. Impact of treatments on soil cation exchange capacity (CEC) sampled in 2023. Horizontal bars indicate least significant difference (p=0.05), ns denotes no significant difference.

The main effect of lime addition resulted in a significant increase in Colwell P in the surface layer only. The difference being approximately 7 mg/kg more Colwell P in limed plots.

Figure 3. Impact of treatments on soil Colwell P (mg/kg). Horizontal bar indicates least significant difference (p=0.05), ns denotes no significant difference.

Economic analysis

After 3 years, there is yet to be a positive cumulative response in profit to any limed treatments compared to the control (Table 1). This is obviously because of the upfront costs of liming, spreading and incorporation followed by the lack of increase in grain yield. However, cultivation has increased profits of some treatments in this paddock. There are many reasons why this may occur, this paddock being a long-term controlled traffic no till system it could be assumed that the cultivation has increased nutrition by mixing stratified layers and enhanced mineralisation as well as softened up any hard layers that could have been impacting plant root growth.

The trial will be sown to lentils in 2025. It is at this phase of the rotation where any benefits from lime would be expected to start to show larger differences in grain yield.

Table 1. Three-year economic analysis of the lime, cultivation and phosphorus treatments in the trial in 2022, 2023.

Discussion

This research highlights the perceived short-term lack of financial gain recorded when applying lime on some soils in SW NSW.

However, it will be interesting to observe any benefits recorded during and after the pulse phase of the rotation, which will be in 2025.

What is clear is that the soil has dropped to a pH level that has started to tie up phosphorous and cause issues with micronutrient availability to the crop, which will no doubt continue to worsen as the pH reduces over time.

The soil data from soil sampled 12 months after lime application indicated that for lime to work effectively on this light textured soil it needs to be incorporated to the desired depth. This was achieved successfully with commercial equipment of a chisel plough and offset disc. It was interesting that the full incorporation from the rotary hoe showed no extra benefits, in fact it resulted in yield reductions in the first year – and this was not due to reduced crop establishment.

This research will continue in 2025 and will provide a fantastic platform for discussion of the economic risks associated with applying costly soil amelioration strategies like lime in low rainfall environments.

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, the author would like to thank them for their continued support.

Contact details

Rachael Whitworth – Research Manager
Ag Grow Agronomy and Research
Email: rachael@aggrowagronomy.com.au

Date published
February 2025