A field comparison of three neutron moisture meters
1993
O'Leary, G.J. (Victorian Dept. of Agriculture, Horsham (Australia). Victorian Inst. for Dryland Agriculture) | Incerti, M. (Victorian Dept. of Agriculture, Walpeup (Australia). Victorian Inst. for Dryland Agriculture, Mallee Research Station)
A study was undertaken to compare 3 neutron moisture meters (NMMs) over a range of counting times on 2 soil types in north-western Victoria. The meters were a Pitman Wallingford 225 (WAL225), a Campbell Pacific Nuclear 503 (CPN503), and a Campbell Pacific Nuclear 501DR (CPN501). The soil types were a grey self-mulching clay and a solonised brown soil (sandy loam). Over the 15-month experiment, standard counts remained relatively constant for WAL225 and CPN501, but CPN503 showed pronounced variation. In field calibrations, the inclusion of depth made significant improvement to the regression of all NMMs irrespective of counting time. No improvements in the calibration were achieved using density corrections from core samples for individual layers. On both soil types, WAL225 and CPN503 performed similarly to each other, and explained 77-76 and 88-74 percent of the variation in soil water content respectively. CPN501 performed poorly, even with a 64 s counting time, and explained only 52-65 percent of the variation when depth was included. Examples of poor calibrations or none at all in water use studies are discussed and typical errors are demonstrated.
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