A drought management research project funded by the Almond Board is being conducted at the Nickels Soil Lab in Arbuckle. Lead researcher is Ken Shackel, UC Davis, who gave a first-season update on the project at the Almond Industry Conference in December. Long-term tree responses to different irrigation levels, various canopy reduction scenarios and actual almond water requirements for survival are being investigated in a 20-year-old orchard where the soil is gravelly and shallow. Treatments were imposed for 2009 only, and the carryover effects on tree growth, tree survival, bloom, and yield will be determined for an additional period of two to four years.
Current findings are:
Almond trees need about 7–8 inches of water to survive, based on one treatment where no water was applied. Water for this treatment came only from rain (2.1 inches) and the soil profile (5.5 inches).
Trees where no water was applied yielded less than one-half than that of conventional irrigated trees (1030 vs. 2224 kernel pounds). These trees produced fewer, smaller and shriveled kernels, and there appears to be some fruitwood dieback.
Treatments also included varying levels of applied water. The deficit treatments were 35 percent and 42 percent of the total water requirements of 40 inches. These treatments affirmed it is best to stretch water use over the season and in proportion to almond evapotranspiration (ETc). There was partial preharvest defoliation with all deficit treatments.
Applications of kaolin (Surround) to improve tree water status and reduce stress are being investigated. There was no reduction in stress when kaolin was applied in the deficit treatments receiving some water.