Amelioration options for water repellent sandplain soils 2011-2014 trial report

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One-off amelioration treatments of water repellent sand are compared in a large scale on-farm demonstration. Treatments resulted in increased grain yields over four seasons, except for one-way ploughing in 2011 and offset discs in 2013. In 2014, lupin yield was increased by 210-430kg/ha for mouldboard ploughing, offset discs and claying treatments; 150kg/ha for rotary spading; with no yield benefit from one-way ploughing. One-off spading was the most profitable option until 2013 after which the benefit was reduced. Claying has maintained its benefit over four seasons.

Background

A range of options exist for managing water repellence in sandplain soils.

Mitigation options include furrow sowing and banded soil wetting agents that assist water entry into repellent soils.

They are relatively cheap to implement each season but need to be repeated every year.

Soil amelioration options include one-off mouldboard ploughing, rotary spading and claying that either physically remove or overcome the topsoil water repellence.

These options can give longer term benefits but are slow and expensive to implement so they need to provide significant long-lasting productivity benefits in order to provide a good return on investment.

Aim

To compare the grain yield responses to a range of soil amelioration treatments applied to water repellent pale deep sand and assess the time required to achieve a return on investment.

Trial details

Table 1 Trial details
Property Sandown, Badgingarra
Soil type Pale deep sand
Crop/variety 2014 - lupin
Paddock rotation Wheat-lupin
Treatments

Control (untreated)

Clay spreading

Mouldboard ploughing

Rotary spading

Offset discs

One-way ploughing

Replicates Repeated controls

Growing season rainfall

(April-October)

2011 - 485mm

2012 - 331mm

2013 - 446mm

2014 - 407mm

This large-scale on-farm soil amelioration trial was established in 2011 on highly repellent pale deep sand and included the following soil amelioration treatments:

  1. Mouldboard ploughing – fully inverts the soil, burying the repellent topsoil and associated nutrients and weed seeds under a layer of wettable subsoil.
  2. Rotary spading – partially buries and mixes the topsoil into the subsoil, importantly spades lift seams of subsoil to the soil surface which act as preferred pathways for water entry.
  3. Offset discs – cultivates the topsoil to a depth of 10-12cm, relatively little engagement with the subsoil, reasonably thorough mixing.
  4. One-way ploughing – cultivates the topsoil to a depth of approximately 15cm, some engagement with the subsurface soil.
  5. Clay-spreading – clay-rich subsoil applied with a multi-spreader and incorporated into the topsoil, clay increases soil surface area and overcomes the water repellence.

Untreated control plots were replicated throughout the trial so that site variation could still be assessed despite not having replicated treatments. The plots are 9m x 190m.

Results

In 2014, the site was sown to lupins.  A shortage of seed meant that the seeding rate was low and reduced the potential yield of the crop, with the untreated plots yielding from 0.76t/ha to 1.35t/ha (Figure 1).

The site had repeated control strips to account for site variation and there was a trend towards increasing yield from the eastern (mouldboard ploughing) to the western (one-way plough) end (Figure 1).

Bar graph showing that lupin yields for the 2014 control and treatment plots range from 0.8-1.46 t/ha. Yield increases for each treatment are shown in table 2.
Figure 1. Lupin grain yield (t/ha) in 2014 for a range of soil amelioration treatments and untreated control strips for severely repellent pale deep sand at Badgingarra.  Trial strips run from east (mouldboard plough) to west (one-way plough) across the site.

Lupin grain yield increased for all treatment plots except one-way ploughing in 2014 (Table 2).

The largest yield increases were achieved by mouldboard ploughing and claying.

The impact of rotary spading seems to be declining although it was one of the better performers in previous years.

Similarly, the impact of the offset discs has been variable over the years and its impact may dissipate quicker than the deeper cultivation methods.

Table 2 Soil amelioration treatment impact on grain yield, net four year benefit and four year return on investment (ROI) for Mace wheat (grain value $280/t for 2011 and $300/t for 2013) and Tanjil lupin ($300/t for 2012 and $320/ha for 2014) grown on pale deep water repellent sand at Badgingarra. Estimated treatment costs were: $120/ha for mouldboard ploughing; $400/ha for clay speading; $150/ha for rotary spading; $30/ha for offset discs and one-way ploughing.
Treatment Change in grain yield (t/ha)

Change in grain yield (t/ha)

Change in grain yield (t/ha)

Change in grain yield (t/ha)

Net four year benefit ($/ha) Four year ROI
- 2011 2012 2013 2014 - -

Mouldboard ploughing

0.09 1.03 0.27 0.35 $410 4.4
Claying (100t/ha) 0.37 1.12 0.40 0.43 $303 1.8
Rotary spading 0.46 1.17 0.41 0.15 $500

4.3

Offset discs 0.10 0.32 -0.01

0.21

$162 6.4
One-way ploughing -0.23 0.38 0.18 0.06 $96 4.2

The net four year benefit and return on investment (ROI) has been determined for the first four years of the trial (Table 2).

Estimated costs for the amelioration treatments are based on owner-operated and contract rates. Benefits associated with some of the treatments, such as weed control for the mouldboard ploughing and reduced wind erosion for the clay spreading treatment, have not been included.

Because of the lupin yield response in 2014 and the relatively low cost, the offset disc treatment has the best return on investment while spading, mouldboard ploughing and one-way ploughing are all similar at this stage.

Overall, the net benefit is highest for spading, mouldboard ploughing and claying.  The high cost of claying has resulted in it having the lowest return on investment so far.

Clay spreading also had impressive yield gains and substantial increases in income (Table 2) but the high cost of this treatment reduced the four year net benefit and return on investment relative to the deep cultivation treatments.

Given that clay spreading can show benefits for decades, net benefit and ROI for this treatment should continue to improve over time and it still only took two years to cover the cost of the treatment.

Comments

Although claying is the costliest of the amelioration options it has shown the most consistent establishment and the soil surface is firm and stable reducing the risk of wind erosion. This may allow greater feed utilisation in a mixed enterprise system.

Monitoring will continue to see if claying treatment starts to out-perform the cultivation treatments.

Acknowledgements

This trial is part of the Department of Agriculture and Food, Western Australia and Grains Research and Development Corporation funded project DAW00204 Delivering agronomic strategies for water repellent soils in Western Australia.

Contact information

Page last updated: Thursday, 10 November 2016 - 2:39pm