1. How Much Water Will I Need
12 October 2016
James Dee

2. Daily Plant Water Requirements
Driven by
Type of plant – sensitivity to water stress
Canopy size – Leaf area
Environmental conditions – Solar Radiation, Wind, Relative Humidity and Temperature

3. Daily Plant Water Requirements
On a high water use day – High solar radiation, high wind speed, high temperature and low relative humidity (January)
On a low water use day – Low solar radiation, low wind speed, low temperature and high relative humidity (June)

4. Seasonal Water Demand Requirements
Change in canopy through the growing season
Annual crops - Length of growing season
Perennial Crops – Deciduous or Evergreen

5. Irrigation Scheduling
What is the Readily Available Water in the rootzone of the crop?
Root Depth = 0.3m RAW = 71mm/m
Rootzone RAW = 0.3 X 71 = 21mm
Daily Water use = ETo X Kc
Maize – Kc of Average ETo in January = 9mm
Average daily crop water use = 1.0 X 9 = 9mm/day
Rootzone Readily Available Water (RRAW) will last 21 ÷ 9 days
= 2.3 days

6. Perennial Pasture Water Requirement
Seasonal Water Demand – 7.5 ML per hectare
Plant type – Perennial, Evergreen
Moderate tolerance to water stress
Stable canopy
Crop water use = ETo X 0.85 = mm/day transpired

7. Millet Water Requirement
Seasonal Water Demand – 4.5 ML per hectare
Plant type – Annual
Moderate tolerance to water stress
Water requirement varies with planting time
Crop stage Kc Root Depth
Initial 20 days m
Development 30 days m
Middle 40 days m
Late 30 days m

8. Maize Water Requirement
Seasonal Water Demand – 5.5 ML per hectare
Plant type – Annual
Moderate tolerance to water stress
Water requirement varies with planting time
Crop stage Kc Root Depth
Initial 30 days m
Development 30 days m
Middle 60 days m
Late 20 days m

9. Forage Sorghum Hybrid Water Requirements
Seasonal Water Demand – 5.5 ML per hectare
Plant type – Annual
Moderate tolerance to water stress
Water requirement varies with planting time
Crop stage Kc Root Depth
Initial 30 days m
Development 30 days m
Middle 60 days m
Late 30 days m

10. DAFWA Websites to help with irrigation management
Calculating seasonal water demand
Irrigation scheduling apps

11. Contact Details James Dee Development Officer
Department of Agriculture and Food, Western Australia
PO Box 1231  Bunbury WA 6230
t +61 (0)   m  +61 (0)
w  agric.wa.gov.au