EXPERIENCE WITH CALIBRATING AN INSTRUMENT FOR ASCERTAINING THE IN SITU WATER CONTENT OF SOIL BY MEASURING THE SOIL ELECTRICAL CAPACITANCE
Instruments for estimating the in situ water content of soils by measuring the soils electrical capacitance, which varies with water content, have recently become commercially available. They are designed for controlling irrigation of crops and are very easy and convenient to use: A sensor is passed from top to bottom of a preformed hole, lined with a plastic tube, and the instrument automatically measures and records the soil electrical capacitance at pre-chosen depths. The measurements are translated into in situ water contents via a calibration established and supplied by the manufacturer. The writer found that the calibration was accurate, provided it was used for measurements in homogeneous sand. However,measurements in fissured clay were very erratic, and water contents established by direct sampling gave results very different to the manufactures calibration. In the end, 70 calibration points were required before a reasonably reliable calibration was established. Unfortunately, the calibration did not remain constant, but changed progressively with time. The manufacturer rightly warns that the built-in calibration should be checked. In fact, it appears that each type of soil should really have its own calibration established,if absolute, rather than relative water content measurements are required. Also, the calibration must be checked regularly to see if it changes with time.
Geoffrey E.Blight
University of the Witwatersrand, Johannesburg, South Africa
国际会议
南京
英文
451-456
2007-04-21（万方平台首次上网日期，不代表论文的发表时间）