GROWTH AND YIELD RESPONSES OF ALMOND (PRUNUS-AMYGDALUS) TO TRICKLE IRRIGATION

Growth and yield responses of developing almond trees (Prunus amygdalu s, Ruby cultivar) to a range of trickle irrigation amounts were determ ined in 1985 through 1987 (the fifth through seventh year after planti ng) at the University of California's West Side Field Station in the s emi-arid San Joaquin Valley. The treatments consisted of six levels of irrigation, ranging from 50 through 175% of the estimated crop evapot ranspiration (ET(c)), applied to a clean-cultivated orchard using a li ne source trickle irrigation system with 6 emitters per tree. ET(c) wa s estimated as grass reference evapotranspiration (ET0) times a crop c oefficient with adjustments based upon shaded area of trees and period during the growing season. Differential irrigation experiments prior to 1984 on the trees used in this study significantly influenced the i nitial trunk cross-section area and canopy size in the 50% ET(c) treat ment and 125% ET(c) treatment. In these cases, treatment effects must be identified as relative effects rather than absolute. The soil of th e experimental field was a Panoche clay loam (nonacid, thermic, Typic Torriorthents). The mean increase in trunk cross-sectional area for th e 3-year period was a positive linear function (r2 = 0.98) of total am ounts of applied water. With increases in water application above the 50% ET(c) treatment, nut retention with respect to flower and fertile nut counts after flowering, was increased approximately 10%. In 1985 a nd 1987, the nut meat yields and mean kernel weights increased signifi cantly with increasing water application from 50% to 150% ET(c). Parti cularly in the higher water application treatments, crop consumptive u se was difficult to quantify due to uncertainty in estimates of deep p ercolation and soil water uptake. Maintenance of leaf water potentials higher than -2.3 MPa during early nut development (March through May) and greater than -2.5 MPa the remainder of the irrigation season (thr ough August) were positively correlated with sustained higher vegetati ve growth rates and higher nut yields.