DETERMINING ALMOND ROOT-ZONE FROM SURFACE CARBON-DIOXIDE FLUXES

Size and distribution of roots in the soil is affected by irrigation method and water quantity and quality. The number of replications required to characterize it at a significant level is so large that it cannot 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 chamber quantifying the spatial distribution Of CO2 fluxes at the soil surface was used to predict root distribution as affected by experimental treatment in an almond orchard. The treatments were two rates of water application by trickle irrigation and two salinity levels. Roots were sampled in a trench 3-m width by 2-m depth that exposed soil profiles. Soil-surface CO2 flux was described by a descending function of the distance from the trunk of the tree. This function was combined to another 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.