By Erica Faber – Technical Manager 

It has become really evident this season the impact a dry spring, summer, and autumn has on our crops. The high amount of small sized fruit seen in the current avocado harvest is just one of the impacts of a lack of soil moisture through our critical fruit set period – October to February.

Even though New Zealand has quite a high rainfall, it does tend to be drier over fruit set. Having a well-managed irrigation system is therefore an important consideration for those wanting to maximise their production.

Drought stress not only impacts fruit size but also production volumes due to higher fruitlet drop. It also has a negative impact on the strength of spring flush which is important for providing resources to the rapidly sizing fruit, protection from sun exposure, and is next year’s fruiting wood. Not pushing enough spring flush will therefore result in lower subsequent yields.

If you are relying heavily on a solid fertiliser programme and have low soil moisture, the tree can’t take up the nutrients it needs to support fruit set, spring flush, and the building of reserves to support the tree through winter. As your tree’s reserves become depleted through winter, leaf health suffers. By the time flowering and fruit set comes around again your tree is already under stress and flowering, fruit set and spring flush is impacted.

Once the tree’s reserves start to be impacted you are getting into a cycle which could take a few seasons to correct.

If you are thinking of installing irrigation, you should use an irrigation engineer or advisor to set up the plan based on an accurate understanding of water constraints, different irrigation zones required, what the end goal is for the size and density of your trees, as well as any plans for future plantings. It’s best to start with where you want to end in terms of your irrigation system. It can be difficult to cut and paste onto an existing system.

As a rough guide for planning water requirements; newly planted trees normally require 30 to 50 litres of water per week depending on the microclimate of your orchard. As the trees grow so will their water requirements and your system needs to be built for this growth. For high density trees where the canopy is kept small, each tree will use about 175 litres a week. For a larger canopy, bigger spacings, or more mature trees you are looking at 240 to 400 litres a week depending on canopy size and crop load.

An irrigation system is only as good as the setup, monitoring of the soil moisture levels, scheduling of adequate irrigation and of course maintenance of the system. Ensure you have a tensiometer or moisture probe correctly installed in each irrigation zone and use professionals to guide you to get the best out of your investment.

If you need help with moisture management on your orchard, please contact the Just Avocados Grower Services Team or Avoworks