Comparison of tillage methods for lime incorporation, Tardun 2016 trial report

Background

Until recently the most common rate of agricultural lime application is one tonne per hectare as a blanket application across the surface of the whole paddock (Taking soil acidity seriously - results of grower surveys 2012, page 118).

This amount is often insufficient to recover and maintain soils above recommended targets of pH 5.5 and 4.8 in topsoil and subsoil, respectively.

As a result of Caring for Country project SP11-01226, growers in Western Australia are increasingly testing pH of soils below 10cm.

Growers understand the importance of lime in restoring soil pH, as seen by the increase in sales of lime in the northern wheatbelt (Liebe group technical audit results 2012).

However, according to Gazey and Andrew, lime sales of 1.1 million tonnes in 2012 (Effective management of soil acidity requires knowledge at the farm, state and national scale) are still less than half that of the 2.5 million tonnes required per year, indicating low adoption of the recommended practice.

Preliminary work by Davies, 2012 (Developing and assessing agronomic strategies for water repellent soils, page 71) has shown the applicability of a number of innovative techniques, including mouldboard ploughing and rotary spading, for incorporation of lime to depth.

Lime on the topsoil can be incorporated to a depth of 30cm enabling management of pH at this depth.

This trial is one of six similar trials throughout the northern wheatbelt. It will help establish best practice methods and promote the effectiveness of these techniques throughout the rainfall zones of the northern agricultural region.

Aim

To showcase to growers different innovative practices for deep incorporation of lime to ameliorate sub surface acidity and improve soil health.

Trial details

Results and discussion

Note; pH discussed as pH (1:5 CaCl₂)

This trial covers three distinct soil types throughout the paddock. The northern section of the paddock is a shallow acid gravel, the middle section a brown sand over gravel of varying depths, the southern section red sandy loam. The results are reported from each of these soil types as each differ in their response to lime and incorporation (Figure 1).

Figure 1 Yield results of lime incorporation trial, Tardun 2016

The inclusion of lime, irrespective of incorporation treatment, has given a significant benefit to yield (Figure 2).

Figure 2 Yield response to lime application (2016)

The addition of lime, 2t/ha or 4t/ha, has increased the surface pH, of the gravel soil in the north of the paddock, from below the target of pH 5.5 to above. Once machine incorporation has been carried out it is shown that 4t/ha lime is required to maintain a higher soil surface pH and increase the mid soil (10-20 cm) pH to a suitable level (Figure 3). The TopDown plough shows a higher subsoil pH below 20cm because one of the three reps has constantly given a high subsoil pH reading each year from the same location. However, this machine would have achieved the deepest lime incorporation and so, even after taking this particular plot result out, it still has the highest subsoil pH after 4t/ha of lime was applied.

Figure 3 Soil pH of north section (acid gravel soil) after harvest 2016, four seasons after lime application and incorporation in 2013

The soil in the centre of the paddock is a loamy sand over gravel. The lime application has increased the topsoil pH but, even after machine incorporation, it has not significantly increased any of the subsoil pH (Figure 4).

Figure 4 Soil pH of mid section (brown loamy sand over gravel soil) after harvest 2016, four seasons after lime application and incorporation in 2013

The incorporation story on the red loamy sand is not as clear because of the inherently high pH. This is because of limestone being present in this area of the paddock which makes it very difficult to draw conclusions from the results (Figure 5).

Figure 5 Soil pH of south section (red loamy sand) after harvest 2016, four seasons after lime application and incorporation in 2013

All sub-surface soils are well above the target of pH 4.8 in the southern area of the paddock. Only two of the topsoil results, involving no lime being applied in the nil and TopDown incorporation treatments, are below the target of pH 5.5 (Figure 5). This shows that it is still worthwhile spreading lime on the surface when required as lime has increased yield in this area (Figure 1).

Comments

Incorporation, irrespective of machine, has sped the increase in sub-surface pH in some soils.

It is necessary to consider the speed of the operation and hectares covered, (ha/hr), along with implementation cost ($/ha) when incorporating lime.

A comparison of the TopDown with the small offset disc on area per day and the impact this has on the whole business, in terms of lime incorporation only, shows:

• TopDown 6m wide x 6km/hr = 3.6ha/hr. After 100hr, 360ha have been covered at a cost of $45 000, assuming $125/ha cost for the implement and process.
• Small offset 12m wide x 8km/hr = 9.75ha/hr. After 100hr, 975ha have been covered at a cost of $39 000, assuming $45/ha cost for the implement and process.

More than twice as much area is covered by the small offset, at a lower cost.

It may be that the cheaper option has smaller yield benefit though greater return given the larger area incorporated. This would allow for increased investment in lime for years following.

Acknowledgements

Thanks to Mark and John Flannagan for managing the trial; also to DAFWA technical services staff for their assistance and SoilTech for soil sampling.

This project is supported by the Northern Agricultural Catchments Council, through funding from the Australian Government’s National Landcare Programme.