Calibrating the neutron moisture meter: Precision and economy

Established laboratory and field calibration procedures for the neutron moisture meter are demonstrated on a uniform soil and alternative, low cost procedures on a duplex, less uniform soil. The effect of field variability on the calibration methodology is discussed with the aim of optimising calibration reliability at minimal cost. The difference between calibration for a soil material, or for a field (a range of soil materials) is considered. In particular, calibration for the estimation of water content change is shown to be a different problem from calibration for the estimation of water content in a variable field. Techniques aimed at detecting field variability problems during calibration are suggested, and methods for optimising the results for the intended use of the instrument are outlined. Pairing of calibration tubes, alternative methods of analysis of calibration data, and use of other information from the field to measure its variability, can improve the precision of calibration procedures to the point where minimal calibration effort, with careful analysis, can provide reliable results. (author)