In dry years, it is important to spread irrigations throughout
the season as much as possible and in proportion to almond
How to best manage irrigation in a potentially short water year is a complex question for almond growers. A workshop at The Almond Conference in early 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. These recommendations will be covered in this newsletter in more detail as the season progresses.
Almond growers anticipating reduced levels of available water should spread out applications over the season, typically mid-March to mid-November, as much as possible in proportion to almond evapotranspiration (ETc). For initial season-long planning,
historical values can be found on the UC’s drought management website. Current Almond Board-funded research is updating these ETc values; therefore, the values 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).
An important consideration in planning is addressing the period of bud differentiation for next year’s crop, which starts about mid-August and continues through the month of September. Moderate stress during this period will have little effect on subsequent years’ nut numbers, but severe stress during bud differentiation has dramatically reduced fruit set the following season, according to research.
Once the season commences, starting at bloom, real-time estimates of ETc (=Kc*ETo) are available using the CIMIS (California Irrigation Management Information System). Starting at bloom, keep a running total, and also account for any meaningful rain and irrigation/fertigation. More information on what to do with these totals will be provided later.
Ideally, for salt management, growers should aim to fill the soil profile prior to bloom. If excess salinity is a concern for your field, fill the soil profile before bloom to at least 4 to 5 feet. However, if salt is not an issue, it is better to save limited water for the growing season, and therefore, it is sufficient for only the top 2 feet of soil to be recharged just prior to bloom. So wait to irrigate as long as possible before bloom to see what winter rains will bring. This strategy will allow for a non-stressed spring push.
Another important first step is to control weeds that compete for water.
When water supplies are severely restricted, impacts to almond trees and crops are unavoidable. Recently completed Almond Board–funded research on drought survival of almond trees led by Ken Shackel (UC Davis), confirms almond trees can survive on very low levels of water — 7.6 inches total from rain plus soil-stored, in his trial. Yields are reduced in the drought year as well as the subsequent year, with reduction proportional to the degree of stress. Fortunately, production recovers by the second season after drought with sufficient water supplies. Severe pruning aimed at compensating for drought stress and other treatments, like kaolin sprays to reduce heat, had no benefit for yield or tree health.