Effects of Partial Rootzone Drying on Sap Flow and Water Balance of Pear Trees Under a Shallow Ground Water Table Condition

The experiments were conducted to test sap flow and water balance of pear trees response to partial rootzone drying under a shallow water table condition. Three treatments, i.e. conventional flood irrigation (CFI), fixed 1/2 partial rootzone drying and the other 1/2 part irrigated (PRD), and alternate 1/2 partial rootzone drying and irrigating (ARDI), were designed. The EnviroSCAN probes and heat pulse sensors were used to monitor soil water dynamics and sap flow respectively. The results shown that the root sap flow of wet side was much larger than that of dry side in PRD and ARDI, also larger than that of the same side in CFI. The root sap flow of dry side in ARDI was restored and improved more quickly than in PRD after rewetting. The trunk sap flow in PRD was smaller than in CFI when one side was drying, and it was larger than in CFI after the dry side rewetting. The trunk sap flow in ARDI was smaller than in CFI, but larger than in PRD during one side drying. The daily water consumption in ARDI and PRD was smaller than that in CFI during the period of only one side irrigated. The compensatory effect for water uptake existed in the roots of wet side for ARDI and PRD, and the ability of root water uptake was enhanced when the dry side rewetting, and it related the duration of root drying. Daily root sap flow was significantly related to reference evapotranspiration, but these relations were markedly different for different surface wetting patterns and different sides. The daily trunk sap flow was also related to reference evapotranspiration, and the ratio of trunk sap flow and reference evapotranspiration was not same for the same soil water content under different surface wetting patterns. Irrigation water use was approximately reduced 1/2 in ARDI and in the drying periods of PRD compared with CFI, but water consumption of trees and trunk sap flow were not reduced the same percentage. The effects of partial rootzone drying on water balance and sap flow were significantly influenced by the shallow ground water table. The capillary contribution from ground water table was significantly increased in ARDI and PRD compared with CFI.