California is in its third year of drought, with 2013 the driest year on record. Late winter rainfall contributed little to seasonal totals, and there is not enough time left in the rainy season to make up for shortages. Under these conditions, growers with reduced levels of water should use all the technology available to optimize irrigations.

How best to manage irrigation in a short water year is a complex question for almond growers. A workshop at The Almond Conference last December looked at irrigation strategies for drought management to help provide almond growers with some answers for season-long water management under different availability scenarios.

Season-long Planning

Applications of available water should be spread out as much as possible over the season, typically mid-March to mid-November, in proportion to almond evapotranspiration (ETc). For season-long planning purposes, historical values can be found on UC’s drought management website at http://bit.ly/almondET. Current Almond Board–funded research is updating these ETc values; therefore, the values5 for the date periods given in the table should be used as the relative proportional ETc over the course of the season, and should be converted to the percent of total season-long ETc, which is the sum of the inches in each column (location).

In scheduling irrigation, the pressure chamber should be used to determine the stem water potential of the trees. Orchard irrigations should not be initiated until the trees reach about -4 bars off their baseline, or about -12 to -13 bars, say Ken Shackel (UC Davis Plant Sciences) and Merced County farm advisor David Doll. Irrigations should be at the percentage of almond evapotranspiration (ETc) that can be afforded — for example, if 15% of water is available for the season, typically mid-March to mid-November, apply 15% ET at each irrigation.

Growers interested in obtaining a pressure chamber can contact their UC farm advisor for options. Information on how to use the chamber is provided on the UC Fruit and Nut Research and Information Center website at http://bit.ly/PressureChamber. Reference baseline values of mid-day stem water potential for your area can be obtained at http://bit.ly/stemwaterpotential.

Almond Board–funded research by Shackel demonstrates that almond trees can survive through the year on as little as 6–8 inches of water (5–10% ET). This included the 2–4 inches of water that were available within the soil profile.