On-farm trial snapshot

Owners: Dane and Natalie Sommerville
Location: Spalding, South Australia
Soil types: sand, loam and clay over clay
Soil pH: 4.4 CaCl₂ (sampling depth zero to 10 centimetres) 
Extractable aluminium: 4.7 milligrams per kilogram (sampling depth zero to 10cm)
Crops: Spartacus barley in 2020; Timok vetch in 2021
Trial treatments:
Control – untreated
Sulfur – applied at one tonne per hectare
Tillage 
Penrice Quarry and Mineral lime – broadcast (3t/ha)
Penrice Quarry and Mineral lime – incorporated with rotary hoe (3t/ha)
Clare Quarry lime – broadcast (4.2t/ha) 
Clare Quarry lime – incorporated with rotary hoe (4.2t/ha)
Penrice Quarry and Mineral lime – broadcast (6t/ha)
Penrice Quarry and Mineral lime – incorporated with rotary hoe (6t/ha)
Clare Quarry lime – broadcast (8.4t/ha)
Clare Quarry lime – incorporated with rotary hoe (8.4t/ha)
Composted cow manure – incorporated with rotary hoe (5t/ha)
Clare Quarry lime and cow manure – incorporated with rotary hoe (8.4t/ha and 5t/ha respectively)
Trial replicates: Four
Evaluation approaches: GreenSeeker™ normalised difference vegetation index (NDVI), plant tissue analysis, soil analysis 
Key result: incorporated lime appears most effective for rapidly improving soil pH which, in turn, increases crop biomass and pulse nodulation rates, and reduces aluminium toxicity.

South Australian growers Dane and Natalie Sommerville were mindful that soil acidification was an issue in the area where they farm near Spalding in the state’s mid-north region.

But the farming couple wanted to find out more about the different soil amendment products and application methods they could use to address the problem.

As a result, they were keen to host a liming trial on their property as part of GRDC-invested research targeting acid soils in South Australia, entitled ‘New knowledge and practices to address topsoil and subsurface acidity under minimum-tillage cropping systems of SA’.

Dane and Natalie were aware that agricultural production would continue to lower the soil pH on their soil types (a mix of sand, clay and loam over clay) and that the problem needed to be addressed sooner or later.

“There is nothing like a trial site on your own property to see how different products work,” Dane says.

“Having representative trial results from your own paddock provides invaluable insights into measures to raise crop productivity.

“We want to be proactive in our approach to acid soil management and were very interested to see the trial results to continue to evolve and adapt our operations to manage soil acidity.”

Tackling acid soils

The couple began by commissioning a soil pH map from Marrabel grower Kym l’Anson, using Veris® mapping technology. This showed that the soil pH was as low as 4.0 CaCl₂ in some parts of the mapped paddock.

Following the paddock mapping, the liming trial was established on the Somervilles’ Spalding farm in May 2020.

Research leader Andrew Harding, a senior consultant on soil and land management with the South Australian Department of Primary Industries and Regions (PIRSA), helped design the on-farm trial, comprising 13 different soil treatments.

“We established a trial with four replicates, each including an untreated control plot and a plot where elemental sulfur was incorporated at a rate of one tonne per hectare to determine the effects of increased acidification,” Mr Harding says.

Since oxidation of the elemental sulfur produces acidity in the soil, the applied sulfur treatment provides an indication of how crop production might be affected in the future if declining soil pH is not addressed.

“The remaining trial plots were designed to test the efficacy of various applications of lime from local sources, as these are what Dane and Natalie would usually use,” he says.

We have included higher rates in the trial to explore whether increased rates of lime would cause any adverse effects.

Lime treatments included Penlime™ from Penrice Quarry and Mineral applied at 3t/ha and 6t/ha, and lime from a local source applied at 4.2t/ha and 8.4t/ha. Two different approaches to application – broadcasting and incorporation – were tested for each of the lime types and rates examined in the trials. The soil amendments were incorporated using a rotary hoe.

“The rate of applied lime generally recommended for this soil type is about 3t/ha using good-quality lime, but we know that in some cases this rate is insufficient to raise the soil pH to 5.5 or above,” Mr Harding says.

“So we have included higher rates in the trial to explore whether increased rates of lime would cause any adverse effects.”

The trial design also included plots in which composted cow manure was incorporated at 5t/ha, as well as plots in which both local quarry lime and cow manure were incorporated at rates of 8.4t/ha and 5t/ha, respectively, because research has shown that compost could help improve the effectiveness of lime applications.

The neutralising value of each lime product was analysed before application and the rates were adjusted depending on the lime quality from different sources to achieve a neutralising value of 100 per cent. For example, the Penrice lime has better quality than the locally sourced lime. So where the Penrice lime was applied at 3t/ha, it had the same neutralising value as the locally sourced lime applied at 4.2t/ha.

Broadcast-only lime treatments aimed to gauge the effectiveness of this approach used by many South Australian growers practicing no-till farming.

Trial findings

The trial site was planted with Spartacus barley following the different treatments in 2020.

As the season progressed, significant visual differences between some treatments were noted. In particular, treatments where lime and compost were incorporated appeared distinctly more vigorous than those where only lime was incorporated. However, at harvest, no corresponding yield benefit was observed, due to a severe frost in October of the 2020 season. Yields were about average from all treatments.

In the 2021 season, the trial site was sown with Timok vetch. The seed was inoculated before sowing and 60 kilograms/ha of diammonium phosphate (DAP) fertiliser was applied.

With 12 months having elapsed since the lime applications, and pulses being generally more sensitive to acid soils, testing and observations during 2021 highlighted some differences between the trial treatments.

“Visual assessments have indicated a significant growth response to the lime treatments, compared to the control, tillage and sulfur treatments,” Mr Harding says.

Normalised difference vegetation index (NDVI) testing was conducted using GreenSeeker™ sensor technology on 24 August 2021 to estimate plant growth (biomass), with two test runs per plot.

‘Acid Soils SA’ project team members (from left) Stephen Loss from GRDC, Brian Hughes from PIRSA, Ruby Hume from the University of Adelaide, Bonnie Armour from PIRSA and Andrew Harding from PIRSA. Photo: Belinda Cay.

Mr Harding says the GreenSeeker™ values, calibrated with biomass cuts, showed the leading lime treatments were nearly twice as productive as the control.

“The best result came from the local quarry lime applied at 8.4t/ha with compost, which produced 1.49t/ha of dry matter compared to 0.75t/ha from the control,” he says.

“Comparison of whole plants showed those grown in the sulfur treatment only produced between 10 and 17 root nodules per plant, while those from the plot treated with incorporated Penrice lime at 6t/ha produced 30 to 37 nodules per plant.”

Plant tissue samples of whole tops were also taken about a week before flowering on 24 August 2021. These tests showed that molybdenum uptake had increased to usual levels on the incorporated lime treatments. Molybdenum is an essential element that is important for legume nodulation and the way legumes process nitrates.

Finally, soil sampling from zero to 10 centimetres was carried out for selected incorporated lime treatments on 26 August 2021, using 10 samples per plot across all four replicated trial plots.

Where lime had been incorporated, topsoil pH had increased to more than 5.5 CaCl₂ in the 15 months since the treatments were applied. The control plot still showed pH 4.4 CaCl_2.

The improved pH in areas corresponded with significantly decreased levels of toxic aluminium and manganese. Higher levels of exchangeable calcium were also noted. There was also an overall increase in total cation exchange capacity.

Future directions

Further soil testing occurred late last year to monitor the ongoing changes in soil pH in terms of soil depth, trace elements and exchangeable cations.

Based on both visual assessments and the GreenSeeker™ NDVI measurements, it would appear that the incorporated lime treatments have delivered better growth responses than broadcast lime. It also appears that all the lime treatments have delivered better results than the untreated control plot and the sulfur treatment.

Dane and Natalie have observed the trial results with interest. Natalie says they had already done a lot of work with pH mapping and created a liming program, and the trials confirmed the value of this approach.

“This has been a great project for us to be part of and it has given us a good insight into how the different products perform,” she says.

“We have gained faith in the effectiveness of the local quarry lime, for example, and found it to be a good product to spread and to handle.”

She adds that the trials have also allowed other growers in the district to observe firsthand how liming can affect yields. However, she cautions against waiting for the trial to be completed before implementing a liming program.

“If you think you might have a soil pH problem you need to take action, as it is not a quick process to fix it,” she says.

“Once soil becomes acidic it can be hard to reverse and deeper soil layers will start to be impacted as well. Liming is a big investment, but you are investing in your land for the long term.”

The lime trial on the Sommervilles’ property will be monitored for several more years to assess the effectiveness and rate of lime movement from the different treatments. The vetch planted last year will be followed by either wheat or barley this year.

More information: Andrew Harding, 08 8842 6231, andrew.harding@sa.gov.au