Citrus Water Uptake Dynamics on a Sandy Florida Entisol

Florida citrus trees must be irrigated to reach maximum production due to low soil water‐holding capacity. In a highly urbanizing state with limited water resources, improved understanding of soil water uptake dynamics is needed to optimize irrigation volume and timing. The objectives of this study were: (i) estimate mature citrus daily evapotranspiration (ET c ) from changes in soil water content (), (ii) calculate citrus crop coefficients ( K c ) from ET c and reference evapotranspiration (ET o ), (iii) determine the relationship of soil water stress coefficient ( K s ) to , and (iv) evaluate how ET c was related to root length density. In a 25‐mo field study using mature Hamlin orange [ Citrus sinensis (L.) Osbeck] trees, ET c averaged 1137 mm yr 1 , and estimated K c ranged between 0.7 and 1.1. Day of year explained more than 88% of the variation in K c when was near field capacity. The value of K s decreased steadily from 1.0 at field capacity ( = 0.072 cm 3 cm 3 ) to approximately 0.5 at 50% available soil water depletion ( = 0.045 cm 3 cm 3 ). Roots were concentrated in the top 15 cm of soil under the tree canopy (0.71 to 1.16 cm roots cm 3 soil), where maximum soil water uptake was about 1.3 mm 3 mm root 1 d 1 at field capacity, decreasing quadratically as decreased. Estimating daily plant water uptake and resulting soil water depletion based on root length density distribution would provide a reasonable basis for a citrus soil water balance model.