A two-dimensional model of root water uptake for single apple trees and its verification with sap flow and soil water content measurements

Root water uptake is an important process of water circle and a component of water balance in the field, and it should be understood better and effectively. A quantitative means of describing root water uptake should be established for efficient water use. The objectives of this research are to develop a two-dimensional (2D) model of root water uptake for single apple trees and to validate the model with sap flow and soil water content measurements in an orchard. Tube-time domain reflectometry (TDR) was used to measure soil volumetric water content, and sap flow sensors based on heat-pulse technology were used to monitor locally the rates of sap flow in the trunk of the apple tree. Also leaf area index (LAI) was measured using the Hemiview system, root density distribution was determined and soil hydraulic characteristics parameters were fitted from measurements. A 2D model of root water uptake was established, which includes root density distribution function, potential transpiration and soil water stress-modified factor. The measured data were compared against the outputs of transpiration rate and soil water contents from the numerical simulation of the soil water dynamics that uses Richards' equation for 2D water flow and the established root uptake model. The results showed an excellent agreement between the measured data and the simulated outputs, which indicate that the developed root water uptake model is effective and feasible. (c) 2005 Elsevier B.V. All rights reserved.