What was it all about?

The economic future of the Australian almond industry depends on effective and efficient use of irrigation water including strategies of deficit irrigation.

This project set up a field experiment in a commercial orchard to compare the effects of eight irrigation treatments on production. Researchers set out to determine minimum levels of irrigation that still maintain productivity as well as irrigation strategies that make production resilient in the face of an increasingly variable water supply.

The irrigation set ups were: 

• Fully irrigated control with 11-14 megalitres per hectare (meeting 100 per cent of plant water needs)
• Three levels of deficit irrigation (55, 70 and 85 per cent of needs)
• High irrigation level (120 per cent).

Initially the project focused on the impact of deficit irrigation on annual production but after three seasons the scope was widened to include yield components like pollination effectiveness, fruit set and spur growth.

Overall, the experiment showed that irrigating at 85 per cent of full irrigation or more, which represents a moderate deficit, has good potential to alleviate water shortages without loss of production.

Specific findings included:  

• Irrigating at 85 per cent or more of full irrigation had no negative impact on kernel size and yield but irrigating at 70 per cent or less decreased kernel yield. 
  
  
• Trees with deficits applied throughout the irrigation cycle adapted more readily to reduced water than those receiving deficits just before harvest.
  
  
• Deficit irrigation had a stimulating effect on fruit set and there was a positive correlation between set and the level of deficit. However, the higher set was possibly compensation for a lower flower number in water deficient relative to control trees. 
  
  
• Water deficits had no impact on the timing of flowering or fruit set but tended to accelerate hull split in line with the level of deficit. 
  
  
• Annual increase in stem circumference was the most accurate indicator of the cumulative effect of irrigation deficit on tree growth.