Clay spreading on water repellent sandy gravel


Research organisatons
Funding source

Trial details

Researcher(s) Giacomo (Jack) Betti and Steve Davies (DAFWA)
Year(s) 2016
Contributor West Midlands Group
Trial location(s) Site 2, Moora, WA
Clay spreading on water repellent sandy gravel locations

To compare different clay spreading and tillage methods for the amelioration of water repellent gravel soils.

Key messages

A summary of the main results from the first season at the Moora trial are presented in Figures 1 and 2.  Due to technical issues, the trial was not seeded at the same time as the rest of the paddock, which was supposed to be used as an untreated control. For this reason, a comparison of the treatments to a control treatment without tillage and clay spreading is not available.  A statistically significant effect of tillage on early plant establishment was found when analysing the plant counts measured about four weeks after sowing (Figure 1, left). All the treatments with the off-set disc (in combination or not with clay spreading) had more plants per linear meter in comparison to the one-way plough treatments. This is likely due to uneven seeding depth following tillage with the one-way plough (deep tillage) compared to the shallower tillage with the off-set disc. Surprisingly, incorporation of subsoil clay at any given rate did not show any significant effect on early plant establishment although this result could be explained by the wetter than usual weather in April-May reducing the severity of soil water repellence.

Again, when looking at the tiller counts recorded 8 weeks after sowing (Figure 1, right) the addition of clay at different rates did not affect the number of tillers. However, the wheat growing in the one-way plough treatments overcame the initial delay in germination giving higher tiller number than those recorded in the treatments with the off-set disc (except for the treatment with 250 t/ha of clay). This trend continued at harvest, with the one-way plough treatments producing higher yields (4.5-4.6 t/ha on average) than the off-set disc treatments (4.1-4.3 t/ha on average) at any given rate of subsoil clay.

Due to the low rates of clay spreading and the low cost of the incorporation methods, all treatments provided a positive return of investments in the first year (ROI= ($/ha gain – $/ha total direct costs) / $/ha total direct costs), based on mean values in Table 1. Not surprisingly, the best ROI in the first year was obtained by the one-way plough treatment without clay spreading (1.42 $/ha), followed by the off-set disc without clay spreading (1.22 $/ha) and the treatments clay spread at 50 t/ha incorporated with one-way plough (1.17 $/ha). These estimates are indicative only, as indirect costs and interests on the initial capital investment are not included in the calculations. For more accurate estimates of ROI, yield results from multiple seasons and crops will be collected in the next 3 years.

Lead research organisation Department of Agriculture and Food WA
Host research organisation West Midlands Group
Trial funding source GRDC DAW00244
Related program N/A

This research is funded by DAFWA and GRDC through DAW00244 soil water repellency, part of GRDC’s Soil Constraints West portfolio of projects. Thanks to Graham White and Erin Cahill for clay spreading, undertaking tillage treatments and provision of trial sites. Thanks also to Joanne Walker, Chad Reynolds and Larry Prosser (DAFWA) for technical support.

Other trial partners Not specified
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Crop type Wheat
Treatment type(s)
  • Soil amelioration
Trial type Experimental
Trial design Randomised,Replicated,Blocked

Moora 2016

Sowing machinery

Nufab multi-spreader, one-way disc plough, off-set disc, digger (clay pit excavation and clay spreader loading).    

Sow date 1 June 2016
Harvest date Not specified
Plot size 17m x 18.3m
Plot replication 3
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Trial source data and summary not available
Check the trial report PDF for trial results.
Observed trial site soil information
Trial site soil testing
Not specified
Soil conditions
Trial site Soil texture
Site 2, Moora, WA Gravelly sand
Derived trial site soil information
Australian Soil Classification Source
Trial site Soil order
Site 2, Moora, WA Tenosol
National soil grid Source
NOTE: National Soil Grid data is aggregated information for background information on the wider area
Actual soil values can vary significantly in a small area and the trial soil tests are the most relevant data where available

Soil properties



Derived climate information

No observed climate data available for this trial.
Derived climate data is determined from trial site location and national weather sources.

Site 2, Moora WA


Some data on this site is sourced from the Bureau of Meteorology

SILO weather estimates sourced from
Jeffrey, S.J., Carter, J.O., Moodie, K.B. and Beswick, A.R. (2001). Using spatial interpolation to construct a comprehensive archive of Australian climate data , Environmental Modelling and Software, Vol 16/4, pp 309-330. DOI: 10.1016/S1364-8152(01)00008-1.

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Trial last modified: 23-07-2019 14:29pm AEST