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SOIL PHYSICS

Water Balance Components in a Mature Citrus Orchard

^a Natural Resour. & Environ. Management Dep., Univ. of Hawaii-Manoa, 1910 East-West Rd., Honolulu, HI 96822
^b Civil Engineering Dep., Suleyman Demirel Univ., Isparta, Turkey
^c Citrus Research and Education Center, Univ. of Florida, Lake Alfred, FL 33850
^d Soil and Water Science Dep., Univ. of Florida, Gainesville, FL 32611
^e Southwest Florida Res. and Education Center, Univ. of Florida, Immokalee, FL 34142

^* Corresponding author (AFares{at}hawaii.edu).

The low water-holding capacity of sandy soils, together with spatial and temporal variations of rainfall, require Florida citrus trees to be irrigated for optimal production. Citrus tree root systems are exposed to various hydrologic conditions because of soil temperature and water gradients due to tree canopy shading and under-tree microirrigation. The main goal of this study was to evaluate water balance components in a mature citrus orchard grown on central Florida ridge soils with special interest in quantifying rainfall interception by a citrus canopy and its effect on effective rainfall estimation. Soil water content was monitored every 30 min at 10-, 20-, 40-, and 80-cm depths in the root zone both under and outside of citrus tree canopies. Microirrigation, rainfall, and weather data were used to calculate effective rainfall, plant water uptake, and deep drainage. We found that the tree canopy intercepted 35 and 50% of the incoming high (5-mm) and low (<5-mm) intensity rainfalls, respectively. Effective rainfall calculated without accounting for the canopy interception effect was overestimated by about 30 and 5% for the dry and wet periods, respectively. Citrus crop evapotranspiration was higher under the tree canopy (irrigated area) than outside the tree canopy (unirrigated area) during the dry season because of supplemental irrigation.

Abbreviations: CitWatBal, citrus water balance model • ER, effective rainfall • ET_c, crop evapotranspiration • ET_o, reference evapotranspiration • IRR, irrigation requirement • TR-21, USDA Technical Release 21