VERY LOW MEDIUM MOISTURE TENSION - A FEASIBLE CRITERION FOR IRRIGATION CONTROL OF CONTAINER-GROWN PLANTS
Hp increases from 0 to 3 cb, as a result of a sharp decline in the medium's hydraulic conductivity (Wallach et al., 1992). At present, determination of hydraulic conductivity in situ is not possible. Alternatively, Φp can serve as a good predictor for leaf water potential. Recently a novel tensiometer, sensitive in the milibar range, was developed. When used in conjunction with an adjustable contactor, it enabled the study of plant response to small changes in Φp. Greenhouse rose was chosen as a model crop.
When tension-controlled- was compared with timer-controlled-irrigation, net photosynthesis rates (Pn) were consistently higher during the warmer hours of the day when irrigation intervals were determined according to a preset Φp, provided that its value was low enough. When compared to timer-controlled irrigation, based on Advisory Service recommendations for rose irrigation, the number of watering pulses was higher. When irrigation is controlled by timer alone, as is the case in most commercial operations in Israel, one can expect either periods of Pn, lower than the potential for the prevailing conditions or inefficient water use. Possible effects on yield and water use efficiency will be discussed.