Delayed Irrigation in Walnuts Improves Tree Health

Research continues to show improved root and tree health in walnut trees when the first irrigation of the season is delayed (photo by C. Parsons)

Research into delayed initiation of irrigation in walnut orchards continues to show benefits for tree health. Similar research in almond production, meanwhile, is producing mixed results.

In a MyAgLife podcast with Taylor Chalstrom, UCCE orchard systems advisor Luke Milliron stressed that use of a pressure chamber and waiting until trees are two to four bars drier than a fully watered baseline before irrigating is showing tremendous potential for tree health and has no effect on production.

“Compared to when growers historically started water, this shows waiting weeks or even a month before starting the first irrigation leads to less water stress later in the year. Growers who are adopting this say that the trees look better,” Milliron said.

In years with adequate winter rainfall, delaying irrigation can be done later than you would think, he added. That is not the case with almond trees. Even though they are a drought-tolerant tree, they can move into severe stress at a much faster rate than walnuts.

Milliron explained that the concept of delaying irrigation in walnuts began with UC researchers and UCCE farm advisors noting poor root health in trees later in the season. There was skepticism at first about the delay concept due to the longstanding belief that trees should start the year with a ‘full tank of water.’ That has proved to be the problem because coming out of dormancy is a time of root growth. Saturating the soil with irrigation at that time affects root growth and leads to stress later in the season due to compromised root health.

Orchard soils also play a part in irrigation decisions. As orchards are planted on more marginal ground, use of a pressure chamber to initiate irrigation integrates soil types with water needs.

Applying the same concept in almond production is not showing the same results. Milliron said waiting to irrigate at the same pressure chamber readings as walnuts has the potential to cause production loss in almonds. The threshold studies will continue, he said, and with the use of newer sensing technologies, including direct measurement of stem water potential, a better trigger can be discovered.

Milliron said the research team would be surveying almond growers to see how and when they decide on the timing of the first irrigation and continue to look for a potential for irrigation delay.

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Cecilia Parsons has spent the past 30 years covering agriculture in California for a variety of newspapers, magazines and organizations. During that time she has been fortunate to witness some of the important events that have shaped this diverse industry and worked hard to examine and explain these events for readers.
When Cecilia first moved to the San Joaquin Valley in 1976, her first journalism job was at a small daily newspaper where she covered “farm news.” From there she branched out to writing for a dairy magazine and a regional weekly agriculture publication.
Cecilia is part of a farming family from the rural community of Ducor where she also raises purebred sheep and is attempting to master versatility ranch horse riding.