Sources of bias in the field calibration of a neutron meter

Greacen, EL; Hignett, C.

doi:10.1071/sr9790405

Cited by 26 publications

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“…Several algebraic expressions (Fox, 1964; Bronswijk, 1990) are available to describe the changes in bulk density as a function of gravimetric water content. A number of empirical relationships have similarly been proposed (Greacen and Hignett, 1979) and tested in the field (Jayawardane et al, 1983) to correct neutron ratios for bulk density effects.…”

Section: Resultsmentioning

confidence: 99%

Dual Field Calibration of Capacitance and Neutron Soil Water Sensors in a Shrinking–Swelling Clay Soil

Fares

Buss²,

Dalton³

et al. 2004

Vadose Zone Journal

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Section: Resultsmentioning

confidence: 99%

Dual Field Calibration of Capacitance and Neutron Soil Water Sensors in a Shrinking–Swelling Clay Soil

Fares

Buss²,

Dalton³

et al. 2004

Vadose Zone Journal

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“…Two separate calibrations were necessary because of the duplex nature of the soil. For the A horizon, the relationship between the volumetric water content (O) and the corrected fractional count rate is given by Greacen & Hignett (1979).…”

Section: Soil Water Measurements By Neutron Probementioning

confidence: 99%

“…In addition, the cracking pattern of the clay drying around the access tubes appeared different from the pattern in the surrounding soil (Greacen & Hignett 1979). The calibration data were fitted by a quadratic function, assuming that the volumetric water content was known without error and that the calibration line passed through the point (1, 1).…”

Section: Soil Water Measurements By Neutron Probementioning

confidence: 99%

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The soil water regime in a young radiata pine plantation in southeastern Australia

Mitchell

Correll

1987

New Forest

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Application. High initial growth rates in plantations may not be sustained beyond canopy closure, when rainfall is insufficient to recharge the soil profile, or restore groundwater to accessible levels. A judicious balance of fertilization, and crop density modified by early thinning, may be necessary to achieve optimum crop productivity and health. A two-year fallow period may be required following felling a mature crop, to allow full recharge of soil water reserves.Abstract. The soil water regime from planting to age seven years beneath plantations of Pinus radiata D. Don on first and second rotation sites has been studied by measuring changes in watertable depth and soil water content. Both plantations received intensive management, which produced very high growth rates.Magnitude and, to a lesser extent duration, of groundwater peaks decreased from planting, and by the time plantations were 5 years old the winter rise was negligible. Within 2 years of planting, soil water in the uppermost 1 m was largely depleted during summer periods, and by the fifth summer available water to 3 m depth was exhausted. A model relating change in water content to time from planting, and cumulative rainfall explained over 95°70 of the variation in water content. Daily changes in water content, which varied from 1.7 to 5.3 mm from winter to summer, related strongly to rainfall but weakly to pan evaporation. No relationship between evapotranspiration and soil water content was found.A rapid early depletion of soil water through vigorous plantation growth resulting from intensive silviculture was observed. This could cause problems in sustaining rapid growth rates beyond canopy closure, where access to groundwater is not possible. A judicious balance of fertilization and crop density, related to site characteristics, would be necessary to achieve optimum productivity.

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“…However, traditional non-nuclear methods such as gravimetric sampling, tensiometers and resistance blocks are still being used, for the same purpose, in field research work. Since the pioneering works of GARDNER and KIRKHAM (1952) and VAN BAVEL (1958, 1963, a wide range of research has been carried out for the evaluation and improvement of the neutron scattering method (see for example IAEA, 1967;1974;1983;VACHAUD et al, 1977;GREACEN and HIGNETT, 1979;SINCLAIR and WILLIAMS, 1979;KASI, 1982;NAKAYAMA and REGINATO, 1982;HODGSON and CHAN, 1987;AMOOZEGAR et al, 1989). Similar attention has been given to the development of tensiometers (e.g., MILLER, 1951;MARSHALL, 1959;RICHARDS, 1960;KLUTE and GARDNER, 1962;VILLA NOVA et al, 1989) and of resistance blocks (e.g., BOUYOUCOS and MICK, 1940;BOUYOUCOS, 1949;TANNER et al, 1949;KIRKHAN and TAYLOR, 1950;PERRIER and MARSH, 1958).…”

Section: Introductionmentioning

confidence: 99%

Comparison of neutron moisture gauges with nonnuclear methods to measure field soil water status

Ki̇rda

Reichardt

1992

Sci. agric. (Piracicaba, Braz.)

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SUMMARY:The neutron moisture gauge is compared with the gravimetric-core soil sampling technique, tensiometers and resistance blocks in relation to stability, Held variability, spatial dependence and number of samples needed at a given level of significance. The variance of field water content measurements with neutron moisture gauges is lower than that of the gravimetric sampling, which therefore requires 2 to 6 times as many samples as the number of measuring sites of the gauges to attain the same level of significance. The space dependence of the measurements made with the subsurface gauge varied depending on the average field soil water content. No space dependence was evident when the water content was lower than 0.2 cm 3 .cnr -3 (50% saturation). Measurements with the tensiometers and resistance blocks manifested no spatial dependence and therefore randomly selected measuring sites can be adapted to Held research work where these methods are to be utilized. Soil water content measurements estimated with neutron moisture gauges showed well defined temporal stability (i.e., the lowest, average and the highest soil water content measurements occur at the same field site) which implies that soil water status of an entire field can be assessed with measurements limited to few locations. Measurements with both tensiometers and the resistance blocks are time variant (i.e., the site giving field average water content changes spatially in time) owing to their relatively smaller measuring domains (i.e., scale of the area which can be represented by a single measurement) as compared to neutron gauges. Therefore it is not possible to define 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. Key Words: neutron gauges, tensiometers, resistance blocks, spatial variability, soil water. COMPARAÇÃO DE SONDAS DE NEUTRONS COM MÉTODOS NÃO NUCLEARESNA ESTIMATIVA DA ÁGUA NO SOLO EM CONDIÇÕES DE CAMPO RESUMO: A sonda de neutrons é comparada com a amostragem gravimétrica, com a tensiometria e com o uso de blocos de resistência, em relação à estabilidade, variabilidade do campo, dependência espacial e múmero de amostras necessárias levando em conta determinado nível de significância. A variância das medidas de umidade do solo obtidas por sonda de neutrons é menor do que para a amostragem gravimétrica, que requer um número de amostras 2 a 6 vezes maior em relação à sonda de neutrons dentro de um mesmo nível de significância. A dependência espacial das medidas feitas com sondas de profundidade variou de acordo com os níveis de umidade do solo. Nenhuma dependência espacial ficou evidente para umidades menores que 0,2 cm 3 .cm 3 (50% da saturação). Medidas com tensiômetros e blocos de resistência não manifestaram dependência espacial e, por isso, a escolha das parcelas para medida facilmente se adaptam a esquemas experimentais nos quais estes métodos podem ser utilizados. Medidas de umidade de solo obtidas por sondas de neutrons m...

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Sources of bias in the field calibration of a neutron meter

Cited by 26 publications

References 0 publications

Dual Field Calibration of Capacitance and Neutron Soil Water Sensors in a Shrinking–Swelling Clay Soil

Dual Field Calibration of Capacitance and Neutron Soil Water Sensors in a Shrinking–Swelling Clay Soil

The soil water regime in a young radiata pine plantation in southeastern Australia

Comparison of neutron moisture gauges with nonnuclear methods to measure field soil water status

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