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

Transcription

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

2 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.

3 Soil water repellence is a large limitation on crop production in Australia. Annual profit forfeit in WA ~$5 million. Arable land effected in WA ~5-1 M ha. Much of the research has been either in the field scale or the micro scale. Western Australian Department of Agriculture and Food. (1) Subedi et al. (1) Western Australian Department of Agriculture and Food. (8)

4 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. Hydrophilic end Hydrophobic end Doerr et al. () Soil water repellency: its causes, characteristics and hydro-geomorphological significance.

5 What can we do about it? Mouldboard ploughing Surfactant application Clay spreading Stubble retention

6 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).

7 3D Electrical Resistivity Tomography (ERT) Creates electrical field with current electrodes and measures specific resistivity at potential electrodes. Stable over the course of the experiment: mineralogy, texture and temperature. Wettable soil The only thing changing is water content. Monitoring resistivity every hours. With calibration we can convert electrical resistivity to volumetric water content.

8 Treatments: Sterilised Natural Control Surfactant Microbes Microbes +Surfactant Control Surfactant Microbes Microbes +Surfactant Sterilisation by gamma irradiation. Model organisms: Bacillus subtilis. Surfactant: SACOA Irrigator. Applied to the water repellent core.

9 ERT (without disturbing) and extra cores for excavation (ground proofing). Watering cycle and excavation (underlined): Wk 1 mm mm mm Wk mm mm mm Wk 3 mm mm mm Excavated soil used for: Soil moisture content - dried at 15. Testing water repellence using the molarity of ethanol droplet test (MED) - dried at for 1 days.

10 Preliminary ERT y (cm) Control Day 1 ( mm) y (cm) Surfactant Day 1 ( mm) y (cm) Microbes Day 1 ( mm) 1 cm x (cm) x (cm) 1 cm x (cm) x (cm) 3 cm x (cm) x (cm)

11 Final ERT y (cm) Control Day 17 ( mm) y (cm) Surfactant Day 5 (8 mm) y (cm) Microbes Day 17 ( mm) 1 cm x (cm) 1 cm x (cm) 3 cm x (cm)

12 Time lapse y (cm) Day 1 ( mm) y (cm) Day 5 (8 mm) y (cm) Day 1 (16 mm) Control x (cm) Surfactant x (cm) Microbes x (cm)

13 Soil moisture (cm3/cm3) Day

14 Recurrence of soil water repellence Depth Control Repellence rating -1 cm Low Very severe 1- cm Moderate Very severe -3 cm Low Severe Surfactants Depth Repellence rating -1 cm Nil 1- cm Nil -3 cm Nil Microbes Depth Repellence rating -1 cm Low 1- cm Low -3 cm Low

15 Summary Monitors hydrological impact of biological and chemical treatments in 3D time-lapse. Surfactant increased the rate of infiltration and held more water (.15 cm 3 /cm 3 more water content). Biological and chemical treatments lower the recurrence of water repellence after drying.

16 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.

17 Measurements: Photogrammetry. Eroded sediment. Surface runoff. Eroded sediment analysis: Particle size analysis. Cation exchange capacity. Total carbon and nitrogen. Absolute macro-nutrients.

18 Preliminary results 1% 8% Control Surfactant Percentage Runoff 6% % % % Very Severely Repellent Soil

19 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.

20 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