Growing avocados – annual water requirements

Page last updated: Thursday, 12 September 2019 - 8:27am

Please note: This content may be out of date and is currently under review.

Salinity and its impact on water requirements

The avocado tree is considered to be highly sensitive to salt and particularly chloride ions. There are some differences between the various races of avocado — avocados evolved in three different regions and are grouped accordingly into Mexican, Guatemalan and West Indian races. The Mexican race being the most sensitive, followed by the Guatemalan with the West Indian race being the least sensitive.

One simple method of determining water quality in terms of total salt is to carry out an electrical conductivity test (EC) usually provided in microSeimens per centimetre (µS/cm).

Preferably, irrigation water for avocados should have an EC of less than 500µS/cm, ideally less than 300µS/cm. Lower quality water of up to and above 700µS/cm can be used, but management practices must be employed to reduce the impact on tree health and therefore fruit yield and quality. Depending on the severity of the salt levels, various strategies such as the use of more tolerant rootstocks, salt leaching, pulse irrigation and the application of gypsum may be used.

Leaching to reduce salt accumulation in the root-zone

Leaching can be used to try and reduce the accumulation of salt in the root-zone. This is achieved by using extended irrigations applying sufficient water resulting in soil saturation of the root zone. The idea is that the water front will take the salts to a point beyond the roots. The frequency of leaching is dependent on water quality and the higher the TDS content (total dissolved solids- a measure of salinity) the more frequently you will need to leach salts. As an example a grower with very salty water flushes every two weeks  by irrigating until a soil tensiometer located at 60 cm depth reads zero tension; indicating that the soil has exceeded field capacity as a water front created by the irrigation has 'flushed' past the tensiometer, taking the salts with it. Avoid unnecessary leaching as this wastes water and will push required plant nutrients beyond the root-zone along with the salt.

Leaching requires additional water be added to the evaporation calculation. If you are planning leaching irrigations, you should allocate an extra 10% to your annual water requirement for every 100µS/cm above 500µS/cm. Therefore a grower in the Wanneroo region with irrigation water with an EC of 1000µS/cm (this is a realistic number for that region) would require an extra 50% on top of the 12.2 ML per hectare already required. Therefore 18.3 ML Ha-1 would be required for an orchard in that location and with that quality of water.

Evaporation effect on dam water storage

Open dam water storage (common water storage for South West WA) is subject to the same evaporation forces as the avocado tree. The volume of stored water lost to evaporation is dependent on the nature and surface area of your dam. There are complex calculators available to assist with determining dam evaporations losses. A simple estimation to account for dam evaporation loss is to double the calculated amount of water required by your orchard.

Note that evaporation from dams also increases the TDS content of the remaining stored water. This should be monitored regularly and taken into account.

Climate variability and resilience planning

While we recommend the use of averages when calculating the expected annual water requirement, climate is variable by nature. As a result, if you are relying on annual rainfall to replenish your water storage, it is recommended that you increase your water requirement calculations by a further 50%. This will allow for seasons with higher than average evaporation and provide for some carry over storage from one season to the next which reduces the impact of winters with reduced rainfall.


This article has been adapted in part from ‘Irrigation requirements of avocado’ (Farmnote 42/88) by Bob Paulin.