A Robust Soil Water Potential Sensor with High Sensitivity and Broad Measuring Range

Agriculture is by far the largest consumer of water worldwide. Soil moisture sensors contribute to the sustainable use of this scarce resource. So far, these devices only measure how much water is present in the soil. The decisive factor, however, is how much water the plants can draw from the soil with their roots, which depends heavily on the composition of the soil. This is the reason why we developed a novel sensor for soil water potential (SWP) measurement. The sensor consists of a highly porous ceramic disc and a new circuit board system for detecting the change in dielectric response of the ceramic discs with changing water uptake. The ceramic was tailored using a novel processing route [1], based on so-called capillary suspensions as precursors, allowing the production of highly open-porous ceramics with characteristic pore size distribution and high mechanical strength. Two different kieselguhr powders were used as ceramic sintering material because they allowed the reproducible fabrication of defect-free sensor discs with high shape accuracy at low sintering temperatures. Ceramic discs with open porosities ranging from 58 to 69 % and broad pore size distributions with pore sizes ranging from 0.5 to 200 µm were manufactured for this new sensor. Drying experiments were carried out in air, in a model soil and in field experiments demonstrating the feasibility and improved sensitivity of the setup.