Submitted to: Applied Engineering in Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 21, 2012
Publication Date: August 14, 2012
Citation: Casanova, J.J., Evett, S.R., Schwartz, R.C. 2012. Design and field tests of an access-tube soil water sensor. Applied Engineering in Agriculture. 28(4):603-610. Interpretive Summary: Measuring the amount of water in soil is important in managing crop irrigation. Current methods of soil water estimation are limited by accuracy, precision, ease of installation and cost. This paper presents the results of field tests of a new sensor design.
Technical Abstract: Accurate soil profile water content monitoring at multiple depths until now, has been possible only using the neutron probe (NP), but with great effort and at infrequent time intervals. Despite the existence of several electromagnetic sensor systems for profile water content measurements, accuracy and spatial representativeness has been precluded by fundamental problems related to soil conductivity and structure effects on the volume explored by the static electromagnetic (EM) field of these sensors, which causes nonrealistic spatial variation in profile water contents. Time domain reflectometry (TDR) methods have the distinct advantage of employing a moving EM field that must pass through and be affected by both the drier and wetter soil structures in which the TDR electrodes are embedded. This paper describes a profiling water content system based on TDR. The design, laboratory calibration, and field-testing is detailed. The sensor system provides unattended, real-time, data acquisition. It can be installed without disturbing the soil around the access tube on the outside of which the TDR electrodes are embedded. However, uncertainty in data due to unreliable mechanical electrical connections shows that improvements must be made before such a system is acceptable for widespread use.