Volumetric Water Content in the Branches and Trunks of Satsuma Mandarin Measured by Time Domain Reflectometry

Abstract

The volumetric water content (VWC) in the branches and trunks of satsuma mandarin (Citrus unshiu Marcow.) was measured using a stainless nail a sensor probe and a portable time domain reflectometry (TDR) soil moisture meter. Two treatments were set up. In one treatment, water stress was applied between May 20 and June 24, then irrigation was conducted twice weekly until July 28. The other treatment was a reverse schedule of irrigation and water stress. Since July 28, water stress was started in both treatments. The water stress was initiated by covering the soil surface with a vapor-permeable sheet. VWC in the branches and trunks changed with the seasons regardless of which treatment had been applied. The VWC increased from the beginning to mid-July and stabilized with little variance until mid-September, when it decreased. The VWC of the branches and trunks changed in accordance with the soil moisture conditions, which were influenced by irrigation, precipitation, and mulching. Variance of measurements is smaller in the trunk than in the branches. The decrease in VWC appeared in mid-July, about three weeks later than the day when the soil was covered with a vapor-permeable sheet. Until harvesting period, the VWC in the branches and trunks in trees with water stress from June 24 to July 28 was lower than that in trees with water stress from May 20 to June 24. Changes in the Brix of the juice were attributed to seasonal differences in the VWC caused by two types of treatment.