Binnu trials explore rotary spading merits

Farme in field walks toward mechanical plough equipment.

Rotary spading on-farm trials show that even a one-off soil inversion has the potential to increase wheat yields on water-repellent sand by at least half a tonne per hectare in the first year.

The trials, on Damian and Clara Harris’s 1750-hectare farm east of Binnu in Western Australia’s northern agricultural zone, were initiated in 2009.

Damian estimates that a third of his topsoil was at that time water repellent, meaning it did not ‘wet-up’ evenly after rain. Persistent dry patches reduced crop establishment, grain production and returns.

When the first-generation grain grower was unable to buy the farm next door as a way to lift production, he started investigating spading as a strategy to improve returns from his existing soils.

Commercially available rotary spaders mix soil to a depth of 400 millimetres. They help crop establishment by burying and diluting non-wetting soil, and bringing naturally occurring loamy subsoil to the surface. Damian decided to put spading to the test.

On-farm trials

Working with Badgingarra grain growers David Hayes and Dennis Martin, Damian established a small replicated plot trial on his farm in 2009 using Dennis Martin’s rotary spader.

The trial, set up by GRDC-supported researcher Dr Stephen Davies from the Department of Agriculture and Food, WA (DAFWA), was spaded and sown immediately after spading on 11 June.

TABLE 1 Soil pH, organic carbon, clay content, penetration resistance in a deep yellow sand at Binnu in 2009. 
 Treatment  Soil pH calcium chloride  Mass of organic carbon (t/ha)  Clay (%)  Penetration resistance (MPa)

 0 to 10  10 to 20  20 to 30  0 to 10  10 to 20  20 to 30  Total 0 to 30  0–10cm  At 20cm  At 30cm
 Control  5.1  4.9  5.0  7.6  4.0  1.6  13.1  3.5  1.8  2.7
 Rotary spader  5.2  4.9  4.8  4.0  3.3  3.4  10.7  4.2  0.6  1.5
 Source: Stephen Davies, Department of Agriculture and Food, Western Australia

Spading was done to a depth of 300 to 400mm at 6 to 6.5 kilometres per hour. Wheat was sown into the spaded soil with knife points set at 100 to 200mm fitted to a 12.1-metre Ausplow DBS (deep blade system) bar on 254mm row spacings.

In 2009, 40mm of rain fell at the trial site before sowing and 9mm on the day of sowing.

The untreated topsoil was mildly acidic (pH 5.1) and was rated as mildly water repellent. A laboratory test indicated the soil had a water droplet penetration time (WDPT) of seven seconds, but poor canola establishment in 2008 indicated that water repellence was worse than what the tests suggested.

At the end of the year, the trial results showed the spaded treatment had more clay in the topsoil (0 to 10 centimetres); less compaction (penetration resistance) (Table 1); more plants; and a higher head count (Table 2) than the non-spaded control.

TABLE 2 Plant density, shoot, head and grain dry weight, head number of hand harvest index cuts and machine harvest grain yields for EGA Bonnie RockPBR logo wheat grown at Binnu in 2009.
Treatment Plant numbers per square metre Hand harvested plant cuts Machine harvest grain yield (t/ha)
Shoot dry weight (t/ha) Head dry weight (t/ha) Grain dry weight (t/ha) Head numbers per square metre
 Control  134  3.4  2.2  1.6  243  1.4
 Rotary spader  145  4.3  2.8  2.1  290  1.9
 LSD (P<0.10)  Not significant  1.1  0.7  0.5  43  0.3
 Source: Stephen Davies, Department of Agriculture and Food, Western Australia

Harvested grain yields in the spaded treatment were 0.5t/ha higher than the non-spaded control. This was achieved on the back of 270mm of growing-season (May to October) rainfall.

On the strength of this, Damian decided to buy his own spader – a four-metre-wide Farmax – with the aim of ameliorating a portion of the farm each year.

In 2010, he hosted another spading demonstration trial on a different part of the farm; again on yellow deep sandy soil.

This time laboratory tests confirmed the soil selected for trial was severely water-repellent with a WDPT of more than 600 seconds (10 minutes).

Damian spaded the test site in April and sowed MagentaA wheat on 23 May. After spading, the soil’s WDPT decreased to 470 seconds.

Dr Davies says even after spading, a WDPT this high would still rank the soil as being severely repellent. However, research has shown that lifting seams of subsoil to the surface through the action of the spader provides more pathways for water entry and allows these soils to ‘wet-up’ more quickly and completely.

The spaded treatment went on to produce 2t/ha more mature shoot biomass and 0.5t/ha more grain than the control, confirming the previous year’s results, despite just 165mm of growing-season rainfall.

Paddock observations


Owners: Damian and Clara Harris

Location: Binnu and Geraldton, WA

Farm size: 1750 hectares

Rainfall (long-term annual average):
300mm; (2011) 451mm

Soil types: 50 per cent yellow deep
sandy earth; 50 per cent red sand and
sandy loam

Soil pH: 5.2 to 7.0 (calcium chloride)

Enterprises: 100 per cent cropping

Typical crop sequence: wheat/wheat/
canola/lupins/wheat or wheat/wheat/

Sowing equipment: 12.1m Ausplow
DBS bar with a 9000L airseeder tank;
254mm row spacings

Last year, Damian spaded a further 200ha of his poorest soils. 

He says that at harvest, after recording 451mm of rain for the year, the spaded areas yielded up to 4.5t/ha – equal to high-production areas that did not need spading, and up to 1t/ha better than non-spaded non-wetting soils.

“To pull into the next paddock and record those results again and again was just phenomenal,” he says.

For 2012, Damian decided not to spade because the season start was too dry.

To those considering spading as a strategy for non-wetting soils, Damian suggests seeking the best available advice. “Also if you are thinking, ‘I will do 200ha’, halve it,” he says. “Do 100ha and apply 2t/ha of lime at the same time.”

He also encourages people to wait for rain before spading as a safeguard against wind erosion.

While trials on poorer sands in other parts of WA have shown that crops may hay off after spading, Damian has not experienced this problem.

Going forward, he estimates he now has only 300ha of soil left to spade on his farm. After that, he may consider spading his better soils to incorporate lime.

Top tips for spading

Dr Stephen Davies from the Department of Agriculture and Food, Western Australia, suggests the following management tips and considerations before spading.

Ensure soil is wet before spading and sow a cereal crop soon after.

Avoid grazing stubbles in the first summer after spading.

Be aware that fine sand containing little clay and few coarse particles is vulnerable to wind erosion.

Consider spading a green manure crop or pasture in spring when the soil is wet and winds are reduced, and then sow a cereal or summer crop.

For pale deep sands or sandy duplex soils, clay-spreading followed by incorporation with a rotary spader or other implement may give a better result than straight spading, particularly in medium to high-rainfall areas.

It is essential that growers use test strips to assess rotary spading on their own farm for several years before undertaking wide-scale adoption. Yield results have been variable across different soil types, properties and seasons. The longevity of the benefits has also varied. As the mixing action of a spader leaves some water-repellent soil near the surface, it is unlikely that the benefits will last beyond five years. In the trial on Damian Harris’s farm the yield benefits have declined over time. In the third year after spading (2011) the yield response was not significant.

Consider other options for managing water repellence. Knife points can concentrate dry repellent soil in the furrow so modifying the sowing equipment and using a banded wetting agent can improve crop emergence in water-repellent soil. In the trial at Damian’s farm mouldboard plough and claying treatments have resulted in longer-lasting benefits.

Spading has the advantage of being easier to use than mouldboard ploughing or claying, which may require more technical skill. Spading leaves some organic matter in the topsoil, which tends to prevent surface crusting that can occur in fully inverted soils and may affect crop establishment in seasons with a drier start. Spading can be useful for incorporating lime, nutrients or clay into subsurface soil.

GRDC Research Codes DAW00204

More information:

Damian Harris, 0428 471 470,;

Dr Stephen Davies, 08 9956 8515,

GRDC Project Code DAW00204

Region West