Citrus Water Uptake Dynamics on a Sandy Florida Entisol
2006
Morgan, K. T. | Obreza, T. A. | Scholberg, J. M. S. | Parsons, L. R. | Wheaton, T. A.
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 (ETc) from changes in soil water content (), (ii) calculate citrus crop coefficients (K c) from ETc and reference evapotranspiration (ETₒ), (iii) determine the relationship of soil water stress coefficient (K ₛ) to , and (iv) evaluate how ETc was related to root length density. In a 25-mo field study using mature Hamlin orange [Citrus sinensis (L.) Osbeck] trees, ETc averaged 1137 mm yr¹, 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 Kₛ decreased steadily from 1.0 at field capacity (= 0.072 cm³ cm³) to approximately 0.5 at 50% available soil water depletion (= 0.045 cm³ cm³). Roots were concentrated in the top 15 cm of soil under the tree canopy (0.71 to 1.16 cm roots cm³ soil), where maximum soil water uptake was about 1.3 mm³ mm root¹ d¹ 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.
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