Sap Flow Response Under Different Soil Moisture Conditions and Irrigation Regimes in Citrus Groves in Southwest Florida.

During the last decade, worldwide water demand for irrigated crops have significantly increased, however, climatologists indicated that water scarcity will be a dilemma in many places around the world. In Florida, citrus is one of the most important perennial crops with an estimated planted area to be 191,131 ha. The objective of this study was to estimate the impact of different irrigation schedule recommendations on citrus sap flow and other crop characteristics and soil moisture contents under the southwest Florida conditions. The study was initiated in May, 2014 on five-year-old sweet orange (Citrus x sinensis (L.) Osbeck) trees located in three commercial groves at Arcadia, Avon Park, and Pacific (Immokalee) in Southwest Florida. Each grove has three irrigation regimes including IFAS (Institute of Food and Agricultural Sciences) recommendation, daily and intermediate irrigation schedules. All groves had received the same volume of water per week based on ET reported by the Florida Automated Weather Station (FAWN). Sap flow measurements were taken for two trees per treatment instrumented with three sensors per tree. Sap flow was measured by the heat balance method using an automated Flow32-1K  flow system (Dynamax Inc., Houston, TX, USA) for 10 days at each site. During sap flow measurements, leaf area, leaf area index, and leaf water potentials were determined. Also, volumetric soil water content (VWC) was measured during the sap flow measurements using data logger EM 50 (Decagon Devices, Pullman, WA, USA) at incremental soil depths of 0-15, 15-30, and 30-45 cm. Results showed significant difference in average daily sap flow, leaf area index, leaf water potentials, and soil moisture measurements among treatments. For example, , during 2015, diurnal sap flow value increased by 91%, 51%, and/or 105% when IFAS irrigation regime was replaced by daily irrigation in Arcadia, Avon Park and Immokalee, respectively.  Average soil volumetric water content (VWC) measured in daily schedule was estimated to be 0.08 cm³ cm^-3, 17% and 41% higher than that measured under intermediate or IFAS, respectively.