Improving soil to optimise water use on farm

WHY THIS PROJECT WAS NEEDED

Soil quality parameters such as pH, CEC and soil organic carbon can affect how much moisture is stored in soils, with healthier soils being more likely to be able to store moisture for later use, such as during a dry spring.

Improving a soil’s ability to store moisture can be achieved by understanding the constraints present in the soil. Once a constraint, such as subsoil acidity, has been identified it can then be managed through lime application or other methods to improve crop production and profitability.

In short: This project helped Murchison region farmers enhance soil quality and maximise the amount of water stored in soils. The project helped identify constraints such as subsoil acidity and demonstrated soil amelioration techniques to improve crop production and resilience against drought.

Project focus

This project involved the establishment of a discussion group for farmers in the Murchison district of Victoria and aimed to address soil quality parameters and how these are linked to storing more rainfall for crop production.

This project increased awareness and knowledge around the identification of key local constraints, such as sub-soil acidity, and involved the demonstration of innovative methods that protect and manage the soil resource. Focus areas included;

• Mapping and ground truthing soil types in paddocks
• Soil constraints in paddocks
• How soil constraints impact crop production and water storage of soils.

To this end, a local trial was established to demonstrate stubble management as a tool to improve soil moisture retention, with the trial also acting as a focus for the discussion group through local field days and workshops.

Overall, the project aimed to provide farmers with a better understanding of their soils and knowledge of how soil can be managed to improve production and water retention and improve resilience for future droughts.

Project outcomes 

Improving soil to optimise water use on farm – trial update 2022

Key points

• An economic analysis showed there were a number of low and high-cost options for stubble retention which provide alternatives to burning.
• A high liming rate of 6.7 t/ha was applied across the demonstration to address the acidity in the 5-15cm layer of soil.
• The liming increased the 0-10cm pH across  all treatments increased to pH 5.8 or  higher, which is the target level of pH to address subsurface acidity.
• The 10-20cm pH results for the unincorporated lime treatments were not consistent with current research and require further investigation.

Riverine Plains worked with farmers in the Murchison area to identify and evaluate seven different stubble retention management strategies to improve soils and store more soil moisture.

The different management techniques were applied side by side and compared with the district practice of burning. Stubble treatments were applied at different dates between wheat harvest (20 December, 2021) and sowing of wheat (cv Scepter) on 8 May 2022.

An economic analysis showed that there were a number of low-cost stubble retention options compared to burning: Treatments 1, 5 and 6 (Table 1). Higher cost stubble retention options included combinations that involved cutting the wheat lower at harvest and incorporating the stubble into the soil (Treatments 2, 3, 4, and 7). Costs associated with burning included nutrient loss and labour.

Table 1 Treatments in the Murchison stubble management trial

^{^}Cost of stubble treatments in addition to farmer ’s normal harvest costs (cost does not include liming. ^#Harvest cut high: stubble is cut at 40cm, harvest rate is 2.2ha/hr; harvest cut low 15-20cm, harvest rate is 4.89ha/hr. ^*Deep incorporation was done using a Performer, which cuts, chops and incorporates stubble to a depth of about 15cm. All cultivated treatments required an additional pre-sowing weed spray compared to uncultivated and burned. ^{^}Header contract rate $400/hr, header fuel rate 60L/hr, fuel cost $1.50/l. ^**Shallow incorporation was done using a multidisc, which chops and incorporates stubble just below the surface. All cultivated treatments required an additional pre-sowing weed spray compared to uncultivated and burned. ^{^}In addition to standard farmer practice of harvesting high.

An example of a higher cost stubble retention option is when there is a need to incorporate a large amount of lime to depth (more than 5cm) below the surface. Although cutting low and incorporating lime is the highest cost option, current thinking is that lime incorporation to depth is a generational activity (>25years). The key is then to maintain pH(CaCl) >5.8 by regular maintenance applications of lime. The crop was cut low was to ensure a better incorporation of the lime, but this also added to the cost. To ascertain the benefit of cutting low, more comprehensive soil testing is required in both Treatments 3 and 4.

Soil moisture was highest after Treatment 2, compared to Treatment 8 and Treatment 3. Higher moisture levels at sowing did not flow through to yield, as water was not limiting in 2022. In a drier year, it would be expected that the stubble-retained treatments would yield more than the burnt treatment due to higher moisture retention.

Yields were extremely variable due to the wet conditions. Treatments 8 and 7 yielded the highest due to their location on better drained soil (i.e this was not a treatment effect). Recent testing of 2022 crop residues by NSW DPI (Tamworth) confirmed that the deep wheat stubble incorporation (Treatment 3) increased Fusarium crown rot infection levels in the following wheat crop, when compared to other stubble management treatments like burning (Treatment 8).

Soil testing at the site showed an acidity issue in the 5-15cm soil layer. To address this, a high liming rate of 6.7t/ha was applied across the demonstration area. Soil testing also indicated that the wet conditions had caused the lime to move to a greater depth in the soil than would normally occur in an average season. In most years, the lime would need to be mechanically incorporated using heavy tillage equipment to mix the lime to the required depth.

The project has given farmers in the Murchison community an opportunity to trial and understand the costs of a number of different stubble management strategies. This gives farmers more options to retain their stubble under different climatic scenarios.

Acknowledgements

This project is jointly funded through the Australian Government’s Future Drought Fund and Riverine Plains. Thanks to our farmer hosts, the Brown family and Lee Menhenett (Incitec Pivot) for contributions of soil and grain testing. Machinery and labour contributions were also made by Graeme Donaldson, Scott Perry and the Brown family. Thank you also to NSW DPI for crown rot testing.

The full results from this trial were reported in Research for the Riverine Plains, 2023 in the article Improving soil to optimise water use on-farm.