Apparent steady state conditions in high resolution weighing-drainage lysimeters containing date palms grown under different salinities

This study presents a novel investigation of long-term apparent steady state conditions under a prescribed leaching fraction criterion. The research was carried out during a 7-year investigation of date palm (Phoenix dactylifera L., cv. Medjool) trees exposed to elevated levels of irrigation water salinity. High resolution weighing lysimeters were designed and constructed to generate an accuracy of ±0.0075 mm. The lysimeters were equipped with precision flux data acquisition that measured the oscillations of their daily water storage difference (ΔW) and evapotranspiration. The leaching fraction was kept constant throughout the study.The results generally confirmed that the assumption of apparent steady state conditions under the preprogrammed irrigation procedure was correct, even though inter- and intra-seasonal climate variations were observed. Measured ΔW oscillated slightly around zero even under high evapotranspiration demands. Drainage water electrical conductivity and leaching fraction were also found to stay fairly constant. The evapotranspiration of the date trees was found to be a function of the potential evapotranspiration, and rather insensitive to changes in the soil water storage (ΔW). Our analysis also indicates that for most practical purposes of monitoring and sustaining apparent steady state conditions, simple low-cost lysimeters, without weighing capability, can serve to monitor and sustain apparent steady state conditions, as long as there is water outflow from the lysimeters.However, the high resolution (high cost) weighing lysimeters proved to be an efficient system for accurate data acquisition, which is necessary for accurate modeling. An annual numerical crop yield model, modified for a date palm field study, was successfully calibrated using data from a 2 month period, and subsequently validated against measured data from the following 8 months. The modified model closely predicted the daily oscillations of drainage water salinity and actual leaching fraction throughout the eight-month period.

► A novel investigation of long-term apparent steady state conditions.
► Utilization of high resolution weighing lysimeters and annual numerical model.
► Apparent steady state conditions were found under prescribed irrigation regimes.
► Leaching fraction, drainage water EC and ΔW remained fairly constant.
► Actual ET of date trees was found to be principally a function of potential ET.