Co-Authors:
Klein, I., Institute of Horticulture, ARO, Volcani Center, Bet Dagan 50250, Israel
Abstract:
In the absence of a convenient and reliable plant water stress indicator which can be used for automatic irrigation, the only rational solution today for scheduling irrigation is to rely on soil matric potential (Ψso) measurements. An automation device connected to the tensiometer (CommonSensor™, patent pending) has been tested in the last two years for controlling irrigation in soilless, and soil planted culture. The CommonSensor logs the data of the soil matric potential continuously (i.e. every several minutes), schedules the irrigation automatically at a pre-set potential (0-50 kPa, i.e. -10, -20, -35 kPa), and controls depth of irrigation by closing the irrigation valve using an appropriate algorithm of time (i.e. x1.5, x2.0, x2.5) required for the tension to decline to -5 kPa. The instrument is battery operated and logs 32.000 data points which can be readily downloaded, and instantly plotted in an Excel spreadsheet. Opening and closing of the irrigation valve is recorded and marked in the data sheet. The CommonSensor improved the irrigation efficiency by reducing percolation, avoiding irrigations under shifting environmental conditions when plant demand declined temporarily, and by automatically adjusting over longer periods of time the volume of irrigated water according to plant demand. Positioning of the CommonSensor (distance and depth) in relation to the water source (dripper or micro sprinkler) needs to be adjusted to the soil mechanical properties to avoid percolation. Under optimal positioning Ψso could be kept close to the pre-set level. The CommonSensor has been used successfully to schedule automatic irrigation in potted (10-70 l) cherry (Prunus avium), peach (Prunus persica) and fig (Ficus carcia) plants bearing fruit in a screen house and in drip irrigated grape (Vitis vinifera) and olive (Olea europaea) outdoors. Load cells connected to 21X Campbell Scientific micro loggers, using potted peach and fig plants, were used to monitor the performance of the CommonSensor. In soilless culture the CommonSensor scheduled automatically the frequency (0-4 times/day), and the timing of the irrigation during the day, according to the pre-set tension, the leaf area in relation to the potted volume, and according to the environmental conditions. The CommonSensor scheduled 1-5 automatic irrigation pulses per day in grape and olive under high water consumption in mid summer. When demand changed gradually (spring, and autumn-winter) frequency and water volume application was automatically adjusted accordingly. Photosynthesis of potted fig plants maintained between 0 and -10, -20 or -35 kPa declined from morning to the afternoon hours, and it was inversely related (R2 = -0.9763 to -1.000) to Ψso, measured simultaneously. Stem water potential (?st), photosynthesis (Pn), stomatal conductance (s) and transpiration (E) of daily drip irrigated grape were highly correlated (R2 = 0.8833 - 1.000) in the morning hours to soil water tension (ca. 0 to - 27 kPa), as monitored by the CommonSensor. At noon, when ?st declined to -9.4 atm, and after irrigation in the early afternoon hours, Ψso ceased to be correlated to Pn, s and E. © ISHS.
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