Estimation of Water Stress by Simple Tensiometer using Satsuma Mandarin and Medium-late Maturing Citrus ‘Harehime’

Abstract

A simple tensiometer is a device for measuring the degree of dryness of soil above pF 2.8, thereby lowering the water level within it. We studied the method to estimate water stress in citrus trees using the simple tensiometer. The results showed that the water level reduction per day using the simple tensiometer provided an indication of water stress in citrus trees. Citrus trees were under no stress, whereas the water potential of soil was above pF 2.8 when the water level of the simple tensiometer began to decrease. Citrus trees were under appropriate water stress associated with an increase in Brix of the fruit if the water level of the simple tensiometer was decreased to about 5 cm a day, at which the leaf water potential (LWP) should be -0.8 MPa or more. If the water level decreased to above 9 cm a day, with LWP being below -1.5 MPa, irrigation was required for citrus trees under high water stress. Brix of the fruit was higher as the integrated value of the water level reduction until harvest time became larger. The simple tensiometer is a useful device for estimating water stress in citrus trees.