Soil Water Use and Apparent Root Efficiencies of Citrus Trees on Four Rootstocks1

The pattern of soil water extraction by ‘Orlando’ tangelo (Citrus paradisi Macf. × C. reticulata Blanco) trees on rough lemon (C. jambhiri Lush.), sour orange (C. aurantium L.), sweet orange (C. sinensis (L.) Osbeck), and ‘Rusk’ citrange (Poncirus trifoliata Raf. × C. sinensis) rootstocks was studied using the neutron moderation method. Root distribution data from a previous study of the same trees were used to compare to water extraction data and to calculate “apparent root efficiencies.” Soil water loss was significantly correlated to feeder root dry weight. The general pattern of moisture extraction showed that the largest water losses initially occurred at the surface with increasing contributions from deeper roots as water from the surface layers was depleted. Roots at each depth and from each rootstock were not equally efficient. The adaptability of trees on the 4 rootstocks to the soil of the experiment site appeared to be related to their respective root distributions and efficiencies.