UC research funded by the Almond Board of California has helped and will continue to help the industry cope with water shortages and drought. Employing regulated deficit irrigation strategies, growers facing restricted water supplies last year were able to produce a crop with no loss in yields. These strategies are summarized in the UC Drought Management Web site: ucmanagedrought.ucdavis.edu/. Specific almond information is under the links – crop irrigation strategies – almonds: ucmanagedrought.ucdavis.edu/Almonds.cfm.
Last year many growers were able to successfully employ a “moderate water stress” strategy outlined in this Web site during the period their water supplies were most restricted, which was June, July and August. This moderate deficit strategy employs deficit irrigation amounting to 50 percent of normal from mid-June to harvest, and meeting normal demand before and after this period. This strategy results in an overall water savings of about 30 percent compared to meeting full season-long evapo-transpiration (ET) demand. Furthermore, this strategy does not have an appreciable impact on current or subsequent yield. Another variation covered in the drought management Web site is simply to apply a uniform deficit rate of 70 percent of full crop water use across the growing season.
Unfortunately, this season many growers are faced with the prospect of even more severe restrictions. In answer to this, the UC Web site covers even more aggressive deficit strategies. A more severe deficit strategy will yield a 50 percent to 60 percent savings in water, but with a reduction in yield the season it is employed and two years afterward.
Lastly there is a “staying alive” strategy. Less is known about this, but research indicates trees can survive with about 12 inches of applied water, depending on stored soil moisture and on how applications are managed and timed according to tree demand during the season. This strategy does not consider tree growth and yield – just tree survival.
With respect to the survival strategy, it is important the trees have water throughout the season in proportion to ET with a primary goal to retain leaves on trees. Recently there have been questions about canopy reduction. Research being initiated at the Nickels Estate will take a look at tree survival and performance under different scenarios. This work will assess the interplay between levels of restricted water (e.g., only stored moisture, 5 inches and 10 inches applied) and levels of canopy reduction.
In this research, current-season survival and carryover effects on bloom and yield for an additional two to four years will be determined. One potential problem to canopy reduction is regrowth. An approach is to wait until the trees are experiencing mild to moderate stress, thus reducing the risk of unwanted regrowth. This research is designed to provide better guidelines for preventing regrowth.
Whichever approach is taken, good management is crucial to success. For instance, it is important to monitor tree water status using a pressure chamber as well as checking soil moisture with an auger, tensiometer, etc. and track almond ET, according to UC water management experts. All of these aspects of irrigation scheduling are included in the UC site. Lastly, a good, well-maintained irrigation system and application efficiency are crucial.
The extended drought irrigation strategies developed by UC can be accessed at the ABC Web site (www.almondboard.com) under Production Research, Drought Management. In addition to a link to the UC Drought Management Web site mentioned above, there is information on UC Cooperative Extension meetings on drought irrigation management being held this spring, and the presentations from these meetings.