DETERMINING ALMOND ROOT-ZONE FROM SURFACE CARBON-DIOXIDE FLUXES

Size and distribution of roots in the soil is affected by irrigation m ethod and water quantity and quality. The number of replications requi red to characterize it at a significant level is so large that it cann ot be included in routine sampling. Our objective was to evaluate the effects of irrigation regimes on almond (Prunus amygdalus Batsch. cv. Butte) root zones from measurements of surface CO2 flux. A dynamic cha mber quantifying the spatial distribution Of CO2 fluxes at the soil su rface was used to predict root distribution as affected by experimenta l treatment in an almond orchard. The treatments were two rates of wat er application by trickle irrigation and two salinity levels. Roots we re sampled in a trench 3-m width by 2-m depth that exposed soil profil es. Soil-surface CO2 flux was described by a descending function of th e distance from the trunk of the tree. This function was combined to a nother regression model estimating the depth of the root zone from CO2 flux measurements. The combined model was used to describe the shape and the size of the root zone. Results show that favorable treatments are characterized by a larger root volume. The depth of the roots may exceed 1.5 to 2.0 m and lateral expansion 2.5 to 4.0 m even when water is applied by drip irrigation.