Crop choice and irrigation strategies have large effects on deep drainage in the Lockyer Valley

Brett RobinsonKevin KodurTim Ellis

supplies 35% of Qld vegetables over 40 000 ha of deep soilsgroundwater withdrawal ~ 47 GL/yearcurrent production = 20 to 30% of potential due to water supplyprice of water = $30 /ML willingness to pay = $200-500 /ML

Courtesy of Leif Wolf

The Lockyer Valley

The Lockyer Valley aquifer and a potential supply route for purified recycled water

Courtesy of Leif Wolf

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).

Surface water storages are relatively small

Lucerne

Use: estimating irrigation water requirements in unmetered areas & deep drainage

Classification algorithm trained with 130 image samples across 51 field sites

Land management has been mapped

Water levels fall after drought years

Our question:How much rainfall and irrigation passes the root zone and, after a time lag, becomes recharge?

Groundwater yield ~ 27 GL/year

Groundwater use ~ 47 GL/year

Volume of PRW available ~ 25 GL/year

IF RECHARGE = 0 GL/year*Net deficit ~ 20 GL/year

IF RECHARGE = 10 GL/yearNet deficit ~10 GL/year

* this is the assumed rate in previous studies

QDPI and DERM estimates

Size matters ! (for recharge)

Washed away….evidence that deep drainage exists

1998 = 24 t/ha2010 = 4 t/ha

Source:

T. Gunawardena, this conference

Purified Recycled Water

Courtesy of Leif Wolf

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

Methods used to estimate deep drainage

Irrigation scenario

Irrigation

(mm/year)

T

(mm/year)

Deep drainage (mm/year)

Fill 50% of drainable porosity

751a 667 265

Fill 25% “ 552b 653

94

Fill deficit only (0%) 516b 653 55

Allow deficit (irrigate small amounts)

543b 628 26

a trigger = 25 mm soil water deficit for high value vegetables and 50 mm for other cropsb trigger = 50 mm soil water deficit for high value vegetables and 60-75 mm for other crops

1998

1999

2000

2001

2002

2003

2004

2005

2006

2007

2008

2009

Year

Regular cropping sequence

Lucerne incorporated

Lucerne + Sorghum incorporated

0

100

200

300

400

500

Dee

p d

rain

age

(mm

)

1998

1999

2000

2001

2002

2003

2004

2005

2006

2007

2008

2009

Year

Regular cropping sequence

Lucerne incorporated

Lucerne + Sorghum incorporated

0

100

200

300

400

500

Dee

p d

rain

age

(mm

)Crops such as lucerne and dryland sorghum can be used to reduce deep drainage

a trigger = 25 mm soil water deficit for high value vegetables and 50 mm for other crops

Cropping sequence

Irrigation(mm/year)

Transpiration(mm/year)

Deep drainage

(mm/year)

Farmer’s sequence

751a 667 265

+ Lucerne 808 826 185

+ Lucerne + Sorghum

721 762 169

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