Calibration of gypsum blocks and data loggers and their evaluation for monitoring soil water status

Abstract

The use of commercial data loggers and gypsum blocks to monitor the matric potential of water in soil was evaluated in the laboratory and at 2 field sites. A set of calibration resistors that simulated a matric potential range of —20 to —2120 kPa was developed that showed close agreement with data that was originally used to develop algorithms for the loggers. Data loggers used in experiments were calibrated against the resistors so output values could be re-scaled to that of the resistor set. Close agreement was found between the matric potential of soil, which was estimated from filter papers, and re-scaled logged matric potential values for gypsum blocks embedded in containers of soil maintained at a range of water contents in the laboratory. Re-scaled logged soil matric potential recorded at 2 field sites also compared favorably with filter paper estimates for soil sampled adjacent to where gypsum blocks were buried. It was concluded that, provided individual data loggers were standardised to the same matric potential scale using either calibrated resistors or soil of known matric potential, the gypsum block technique provided an economical and accurate measure of soil water status.