Citrus irrigation recommendations in Western Australia

Page last updated: Friday, 6 September 2019 - 3:13pm

Please note: This content may be out of date and is currently under review.

Daily water requirements

There is good correlation between plant water requirements and evaporation. Citrus trees use about 70% of evaporation. If evaporation is 10mm, the trees will use 7mm of water from the soil root zone volume.

Daily water use (mm) = Evaporation (mm) x 0.7

If you use sprinkler systems which irrigate the under-canopy area evenly with a known application rate, use this formula to calculate daily water requirements.

Drip irrigation systems only water a portion of the under-canopy area so daily water requirements should be calculated in litres.

Converting water use to litres

To convert millimetres of water use to litres, multiply daily water use in millimetres by the canopy area at ground level.

Daily water use (L) = Evaporation (mm) x 0.7 x Canopy ground area (m2)

Water use is proportional to the area of exposed leaf, which relates to the area of land covered by the canopy. Calculate canopy ground area in square metres by measuring the horizontal dimensions. If the trees are growing in a hedge and canopies are touching, multiply the tree spacing by the average canopy width along the row. If the canopies do not touch, work out the area as a circle.

Measuring canopy size

Measuring canopy size

Tables 1 and 2 show the average daily irrigation requirements of citrus trees in litres for different canopy sizes at Wokalup and the Upper Swan. Figures have been rounded. Average evaporation rates were taken from the Bureau of Meteorology website.

Table 1 Average daily water requirements in litres per day at Wokalup
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Average monthly evaporation (E)

9 8.6 6.8 4.4 2.7 2.1 2.3 2.5 3.2 4.4 6 7.9

Small tree 1m² canopy

(E x 0.7 x 1m²)

Average daily irrigation requirement (L/tree) 6.5 6 5 3 2 1.5 1.5 2 2.5 3 4.5 5.5

Medium tree 9m² canopy

(E x 0.7 x 9m²)

57 54 43 28 17 13 14.5 16 20 28 38 50

Large tree 16m² canopy

(E x 0.7 x 16m²)

101 96.5 76 49 30 23.5 26 28 36 49.5 67 88.5

Table 2 Average daily water requirements in litres per day at Upper Swan
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Average monthly evaporation (E)   9.9 9.1 7.3 5 3.1 2.5 2.5 2.6 3.3 4.8 6.7 8.5

Small tree  1m² canopy

(E x 0.7 x 1m²)

Average daily irrigation requirement (L/tree) 7 6.5 5 3.5 2.5 2 2 2 2.5 3.5 5 6

Medium tree 9m² canopy

(E x 0.7 x 9m²)

62.5 57.5 46 31.5 20 16 16 16.5 21 30 42 53.5

Large tree 16m² canopy

(E x 0.7 x 16m²)

111 102 82 56 35 28 28 29 37 54 75 95

Imperial mandarins

Varieties with narrow, upright growth habits, such as Imperial mandarins, will require slightly more water than that calculated according to canopy ground area. Use the calculations above as a base and fine-tune the schedule using soil moisture monitoring.

Contact information

Kevin Lacey
+61 (0)8 9368 3546