Irrigators in the Central Queensland avocado growing region are facing tough decisions due to changes in water availability.

When water is in short supply a range of decisions may need to be made including:

• the purchase of additional water from a low availability market
• prioritise water onto preferred patches
• giving other patches reduced volumes with consequent reductions in production
• abandoning poorly performing patches, and
• possibly removing plantings of lowest priority and bringing forward redevelopment plans.

The success of a reduced irrigation strategy must consider the impacts in both the current season(s) and subsequent seasons. This is particularly the case with avocados, as the effects of inadequate moisture are not temporary. A survival mechanism exists where moisture stress leads to blockages in the tree’s water conducting tissues until new conductive tissue is grown (often termed ‘drought memory’). Water movement can be reduced for up to two years after the stress period has occurred.

Avocados have relatively high water requirements compared to other horticultural crops, and correct irrigation is the most important cultural practice in their production.

Avocado trees have a relatively shallow root system. Water uptake can be inefficient, with trees unable to search for and extract water that is tightly held to soil particles. Therefore, this crop is less forgiving of poor irrigation practices. About 90% of the roots typically occur in the top 15cm, and little water can be extracted from soil that is drier than -20kPa.

There are some things that growers can adopt relatively quickly which may result in some water savings depending on current irrigation management. These savings are generally minor, the main benefit is ensuring a higher certainty of the water that is available reaching the crop. Some of these include:

• calculating block by block water budgets
• checking and conducting maintenance on the irrigation system to reduce leaks or remove blockages
• installing irrigation scheduling and recording devices such as soil moisture monitoring and irrigation controllers
• reducing canopy size
• mulching the wetted strip
• reducing the wetted area by changing sprinkler heads
• irrigating at night to reduce evaporation
• conducting full weed cover
• managing orchard variability due to soil type and irrigation system performance.

For irrigators who are already highly efficient, there may be very little that can be done to save significant amounts of water. Water budgeting and purchasing additional water to deliver full production potential to selected blocks, canopy reduction, patch prioritisation and possibly bringing forward redevelopment plans are the most effective strategies to be considered when managing low water availability.

Avocado growers in the Mallee experienced significant reductions to water allocations in 2006-2008. Various water saving methods were adopted, including ‘staghorning’ (Figure 1). These practices had mixed outcomes, with irrigators expressing alternative actions if subjected to the same conditions in the future.

More information

For a detailed account of “Managing Avocados with less water” visit the Agriculture Victoria’s facts sheet – https://agriculture.vic.gov.au/farm-management/water/irrigation/managing-with-less-water/avocado-in-the-mallee.

Read more about irrigation in the Growing module of the BPR.

This article was prepared for the Autumn 2021 edition of Talking Avocados.