Measuring soil moisture dynamics in an irrigated orchard by time domain reflectometry method

Knowledge of the dynamic behavior of soil water content is essential for an understanding of the soil-plant-atmosphere system. The continuous and precise measurement of soil water content, is often a key for the interpretation of results measured in field, laboratory and greenhouse experiments. This is especially true for studies on water consumption by plants and its role in the scheduling of irrigation. The direct measurement of soil moisture content is advantageous over the other commonly used method, where the measured matrix potential is transformed into moisture content by the soil's retention curve. The purpose of this study was to monitor soil moisture dynamics during and between irrigation by the Time Domain Reflectometry (TDR) method. The experiment was conducted at the experimental farm at the Faculty of Agriculture in Rehovot, Israel. The TDR system used consists of a Tektronix 1502B cable tester interfaced to a Campbell Scientific CR10 data logger and a Campbell Scientific SDMX50 multiplexer. The TDR measurements of changes in the volumetric water content with time, θ(t), provide an excellent picture of soil-moisture dynamics caused by free drainage and water uptake by roots during and between the irrigation events. There is a sharp decrease in moisture content at the end of the irrigation due to the deep percolation, followed by a moderate decrease mainly due to root uptake. The effect of non-uniform irrigation on deep percolation and root uptake can also be observed by the measurements. The TDR can be further used to study the dynamics of soil moisture in the root zone, as related to other processes, and with further research, for on-line irrigation control.