Mary-Anne Lowe, PhD Candidate.UWA School of Agriculture and Environment.

Acknowledgements

Special thanks to my supervisors.Matthias Leopold - UWA School of Agriculture and Environment.

Gavan McGrath - Ishka Solutions.

Falko Mathes - Bioscience WA.

Meng Heng Loke - Geotomo Software.

and Daniel Murphy - UWA School of Agriculture and Environment.

CRC for Polymers postgraduate scholarship.

UWA Postgraduate Award and top-up scholarship.

Soil water repellence is a large limitation on crop production in Australia.

Annual profit forfeit in WA ~$250 million.

Arable land effected in WA ~5-10 M ha.

Much of the research has been either in the field scale or the micro scale.

Western Australian Department of Agriculture and Food. (2008)

Western Australian Department of Agriculture and Food. (2012)

Subedi et al. (2012)

Doerr et al. (2000) Soil water repellency: its causes, characteristics and hydro-geomorphological significance.

Limits infiltration of water.

Causes unstable wetting fronts.

Variable both spatially and temporally.

Caused by organic molecules coating the surface that have a hydrophobic and a hydrophilic end.

Hydrophobic endHydrophilic end

What can we do about it?

Stubble retention

Surfactant applicationMouldboard ploughing

Clay spreading

The physical effect of biological and chemical treatments on water repellent soils.

Research Aim:To understand the hydrological effects of, and mechanisms responsible for, the breakdown of water repellence in soils.

Method:Monitoring the spatial changes in soil moisture over time, using non-destructive, 3D electrical resistivity tomography (ERT).

Creates electrical field with 2 current electrodes and measures specific resistivity at 2 potential electrodes.

Stable over the course of the experiment: mineralogy, texture and temperature.

The only thing changing is water content.

Monitoring resistivity every 2 hours.

With calibration we can convert electrical resistivity to volumetric water content.

3D Electrical Resistivity Tomography (ERT)

Wettable soil

Treatments:

Sterilisation by gamma irradiation.

Model organisms: Bacillus subtilis.

Surfactant: SACOA Irrigator.

Applied to the water repellent core.

Sterilised

Control Surfactant Microbes Microbes +Surfactant

Natural

Control Surfactant Microbes Microbes +Surfactant

ERT (without disturbing) and extra cores for excavation (ground proofing). Watering cycle and excavation (underlined):

Excavated soil used for:

Soil moisture content - dried at 105 .

Testing water repellence using the molarity of ethanol droplet test (MED) - dried at 40 for 14 days.

Wk 1 2 mm 2 mm 4 mm

Wk 2 2 mm 2 mm 4 mm

Wk 3 2 mm 2 mm 4 mm

x (cm)

x (cm)

x (cm)

4

2

00 2 4

y (cm)

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0 0 2 4

Day 1 (0 mm)

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2

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0 2 4

Control

0 – 1 cm

1 – 2 cm

2 – 3 cm

Microbes

y (cm)

4

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0 0 2 4 x (cm)

Day 1 (0 mm)

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00 2 4 x (cm)

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00 2 4 x (cm)

y (cm)

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0 0 2 4

Day 1 (0 mm)

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00 2 4

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0 2 4

SurfactantPreliminary ERT

0 – 1 cm

1 – 2 cm

2 – 3 cm

y (cm)

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2

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0 2 4

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0 2 4

0 2 4

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Day 17 (20 mm)

Control

0 2 4 x (cm)

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0

0 2 4 x (cm)

y (cm)

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0

0 2 4 x (cm)

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0

Day 17 (20 mm)

Microbes

0 2 4

4

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0

0 2 4

y (cm)

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2

0

0 2 4

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Day 5 (8 mm)

SurfactantFinal ERT

Time lapse

Control

0 2 4

y (cm) 4

2

0

Day 1 (2 mm)

0 2 4

y (cm) 4

2

0

Day 5 (8 mm)

0 2 4 x (cm)

y (cm) 4

2

0

Day 12 (16 mm)

0 2 4

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Microbes

0 2 4

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00 2 4 x (cm)

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0 2 4

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Surfactant

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0

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0.05

0.1

0.15

0.2

0.25

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Soil moisture (cm3/cm3)

Day

2 2 4 2 2 4 2 2 4

Recurrence of soil water repellence

ControlDepth Repellence rating

0-1 cm Low – Very severe

1-2 cm Moderate – Very severe

2-3 cm Low – Severe

SurfactantsDepth Repellence rating0-1 cm Nil1-2 cm Nil 2-3 cm Nil

MicrobesDepth Repellence rating0-1 cm Low1-2 cm Low2-3 cm Low

Monitors hydrological impact of biological and chemical treatments in 3D time-lapse.

Surfactant increased the rate of infiltration and held more water (0.15 cm3/cm3 more water content).

Biological and chemical treatments lower the recurrence of water repellence after drying.

Summary

Erosion evolution on water repellent soils.

Research Aim:To be able to measure the erosion and runoff on a water repellent soil, noting the type of loss we are incurring and the position on the slope where it is originating.

Method:Using photogrammetry to monitor the spatial changes of the soil surface over time and collecting water and sediments for loss analysis.

Measurements:

Photogrammetry.

Eroded sediment.

Surface runoff.

Eroded sediment analysis:

Particle size analysis. Total carbon and nitrogen.

Cation exchange capacity. Absolute macro-nutrients.

2˚ 2˚

4˚ 4˚

Preliminary results

0%

20%

40%

60%

80%

100%

Very Severely Repellent Soil

Percentage Runoff

Control

Surfactant

Summary - Expectations

Water repellent soils do not produce runoff in the same way as wetting soils.

Erosion pathways more dynamic.

Increased overland flow increases erosion.

Measures associated with a healthier soil will be negatively impacted with erosion.

Conclusions

Soil water repellence impacts:

soil moisture content.

soil moisture distribution.

erosion (contributing to losses of soil and organic matter).

The use of chemical treatments (surfactants) increases infiltration, decreasing runoff, decreasing erosion.

Increasing productivity without increasing environmental degradation.

We need to weigh up our options