Comparison of tillage methods for lime incorporation, West Binnu 2016 trial report

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Using tillage to incorporate lime improves the rates of reaction and increases subsurface pH sooner than spreading lime on the surface alone.

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.

A 2015 phone survey of 20 growers, conducted by this project, found the majority of growers are now using 2t/ha in order to speed the repair of soils.

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 work was to establish best practice methods and promote the effectiveness of these incorporation 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

Table 1 Trial details, West Binnu trial 2016 (third year of trial)
Property Kirra Plains, West Binnu
Soil type Yellow sandplain
Crop / variety Not cropped
Paddock rotation 2013 canola, 2014 wheat, 2015 wheat, 2016 pasture
Treatments

2014 Lime at 0, 2 and 4.5t/ha

2014 Incorporation method: nil, offset disc, one way plough, mouldboard plough, deep rip, Grizzly Deep Digger®

Replicates Two

Growing season rainfall

2016 - Third season (DAFWA Binnu station)

January – March 50mm

April – September 296mm

Results from the West Binnu trial

Lime incorporation worked well, particularly with the use of the Deep Delve and the Offset
Figure 1 Soil pH profiles (2016) from each of the treatments at West Binnu three seasons after lime application and incorporation

Comments on the West Binnu Trial

2016 (Year 3)

Unfortunately the trial area was not cropped in 2016 and so we were unable to get any plant data, in particular yield, in relation to the lime incorporation treatments.

However, soil samples were still taken at the end of the year to look at the effect lime incorporation has had after three seasons. There was significant difference in regard to lime treatment all the way down the soil profile. This can be seen to some degree in the nil treatment where the effect of lime has increased the soil pH down to the depth of the midsoil (10-20cm) as seen in Figure 1.

The soil pH samples for the deep delve treatment seem to have given the best result, where lime was successfully incorporated to the greatest depth (30-40cm). The offset and mouldboard also delivered successful incorporation down to 20-30cm (Figure 1). The one way plough improved subsoil pH, but just not to the same extent as the other machines already mentioned.

The soil pH results for the deep rip treatment didn't support the lime rates that were applied. The deep ripper tines did not displace a large amount of soil, nor were they modified to hold open the slot for topsoil burial. It is possible that this result is from unrepresentative sampling at the time of soil collection, but this is hard to say when even the topsoil samples shows lower soil pH on those areas where lime was applied. Soil samples from previous seasons have shown benefit of lime incorporation using a deep ripper so future samples from this trial will be interesting.

Acknowledgements

Thanks to Rhys Carson for managing the trials at West Binnu; 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.

The West Binnu trial is part of the 'Demonstrating principles of ameliorating subsurface pH to improve soil health project' (INNOV–292) delivered in partnership with Northern Agricultural Catchments Council WA (NACC).

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