Comparison of neutron moisture gauges with non-nuclear methods to measure field soil water status
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Joint FAO/IAEA Division of Nuclear Techniques in Food and Agriculture IAEA P.O. Box 100, Vienna, Austria
Center for Nuclear Energy in Agriculture (CENA), University of Sao Paulo 13.400 Piracicaba (SP), Brazil
Publication date: 2020-09-23
Int. Agrophys. 1992, 6(1-2): 77–87
The neutron moisture gauge was compared with the gravimetric-core soil sampling technique, tensiometers and resistance blocks in relation to temporal stability, field variability, spatial dependence and number of samples needed for a given level of accuracy. The variance .of field water content measurements with neutron moisture gauges was lower than that of the gravimetric sampling, which therefore required 2 to 6 times as many samples as the number of measuring sites of the gauges to attain the• same level of accuracy. The space dependence of the measurements made with the subsurface gauge varied depending on average field soil water content. No space dependence was evident then the water content was lower than 0.2 cm3 cm–3 (50% saturation). Measurements with the tensiometers and resistance blocks manifested, however no spatial dependence and therefore randomly selected measuring sites can be adapted to field research work where these methods are to be utilized. Soil water content measurements estimated with neutron moisture gauges showed well defined temporal stability which implies that soil water status of an entire field can be assessed with measurements limited to a few sites. The measurements with both tensiometers and the resistance blocks are time variant owing to their relatively smaller measuring domains as com •pared to neutron gauges. Therefore, it is not possible to calibrate the measuring sites of the tensiometers and resistance blocks as to assess soil water status of the entire field as it could be done with the neutron gauge.