Crop choice and irrigation strategies have large effects on deep drainage in the Lockyer Valley. Brett Robinson
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A presentation at the WCCA 2011 event in Brisbane.
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Crop choice and irrigation strategies have large effects on deep drainage in the Lockyer Valley. Brett Robinson
- 1. Crop choice and irrigation strategies have large effects on deep drainage in the Lockyer Valley Brett Robinson Kevin Kodur Tim Ellis
- 2. The Lockyer Valley • supplies 35% of Qld vegetables • over 40 000 ha of deep soils • groundwater withdrawal ~ 47 GL/year • current production = 20 to 30% of potential due to water supply • price of water = $30 /ML • willingness to pay = $200-500 /ML Courtesy of Leif Wolf
- 3. The Lockyer Valley aquifer and a potential supply route for purified recycled water Courtesy of Leif Wolf
- 4. Surface water storages are relatively small Catchment Area of alluvium (ha) Storage (ML) ML/ha Lockyer Creek 17,090 22,540 1.31 Laidley Creek 6,500 11,600 1.78 Tenthill Creek 3,970 17,720 4.46 Flagstone Creek 2,050 9,330 4.55 Sandy Creek 1,770 1,630 0.91 Ma Ma Creek 1,240 1,780 1.43 Total 32,600 64,600 1.98 Source: Department of Natural Resources, (1994).
- 5. Land management has been mapped Use: estimating irrigation water requirements in unmetered areas & deep drainage Lucerne Classification algorithm trained with 130 image samples across 51 field sites
- 6. Water levels fall after drought years
- 7. Our question: How much rainfall and irrigation passes the root zone and, after a time lag, becomes recharge?
- 8. Size matters ! (for recharge) Groundwater yield ~ 27 GL/year Groundwater use ~ 47 GL/year Volume of PRW available ~ 25 GL/year QDPI and DERM estimates IF RECHARGE = 0 GL/year* Net deficit ~ 20 GL/year IF RECHARGE = 10 GL/year Net deficit ~10 GL/year * this is the assumed rate in previous studies
- 9. Washed away…. evidence that deep drainage exists 1998 = 24 t/ha 2010 = 4 t/ha Source: T. Gunawardena, this conference
- 10. Purified Recycled Water Courtesy of Leif Wolf
- 11. Methods used to estimate deep drainage Water balance simulations using HowLeaky? • Daily-time step • Inputs = rainfall and irrigation • Outputs = runoff, soil evap, transpiration, deep drainage • Parameters = climate, soil, veg, tillage, irrigation • The crop sequence provided by a skilled farmer (beetroot, broccoli, cotton, mung bean, sweet corn (all irrigated) and wheat (dryland)). • Soil = a Black Vertosol
- 12. Irrigation Irrigation T Deep scenario (mm/year) (mm/year) drainage (mm/year) Fill 50% of 751a 667 265 drainable porosity Fill 25% “ 552b 653 94 Fill deficit only (0%) 516b 653 55 Allow deficit 543b 628 26 (irrigate small amounts) a trigger = 25 mm soil water deficit for high value vegetables and 50 mm for other crops b trigger = 50 mm soil water deficit for high value vegetables and 60-75 mm for other crops
- 13. Crops such as lucerne and dryland sorghum can be used to reduce deep drainage 500 Regular cropping sequence Lucerne incorporated Deep drainage (mm) 400 Lucerne + Sorghum incorporated 300 200 100 0 2004 2005 2006 2007 2008 2009 1998 1999 2000 2001 2002 2003 Year
- 14. Cropping Irrigation Transpiration Deep (mm/year) (mm/year) sequence drainage (mm/year) Farmer’s 751a 667 265 sequence + Lucerne 808 826 185 + Lucerne 721 762 169 + Sorghum a trigger = 25 mm soil water deficit for high value vegetables and 50 mm for other crops
- 15. Future questions: 1. Spatial distribution of deep drainage 2. Spray vs drip, plastic vs bare 3. More chloride profiles (?) 4. Can we improve our input parameters? Cheaply? 5. Economics of veges vs lucerne vs dryland