Components of variance involved in estimating soil water content and water content change using a neutron moisture meter

Soil Research ◽  
1979 ◽  
Vol 17 (2) ◽  
pp. 237 ◽  
Author(s):  
DF Sinclair ◽  
J Williams
Keyword(s):  
Water Content ◽  
Soil Water ◽  
Total Variance ◽  
Calibration Error ◽  
Location Error ◽  
Instrument Error ◽  
Moisture Meter ◽  
Site Heterogeneity ◽  
Neutron Moisture ◽  
The Mean

In order to rationalize the allocation of resources in the estimation of soil water content using the neutron moisture meter, it is essential to have a thorough understanding of the sources and magnitudes of the variance components. An error analysis, taking into consideration current technology and methodology, identifies three components of total variance, attributable to: location error due to site heterogeneity with respect to soil water and random error associated with positioning the probe; calibration error; and instrument error. Data from three locations illustrate that the location variance is the major source of random error in the total variance of an individual estimate. For the total variance of the mean over a site containing n sample estimates, the large location component is reduced by a factor of n such that in many circumstances it will reduce to the same order as the calibration component which is independent of n. This is particularly true for field calibration. The instrument error and that error introduced by the use of count rate ratio are small and contribute in a very minor way to the total variance of the mean. The analysis reveals that the nature of the relationship between the magnitude of the location error and the calibration error is dependent on site heterogeneity, the value of n and the precision of the calibration equation.

Screening potato clones for resistance to common scab (Streptomyces scabies) in the field

1972 ◽  
Vol 79 (1) ◽  
pp. 75-81 ◽  
Author(s):  
F. A. Langton
Keyword(s):  
Water Content ◽  
Soil Water ◽  
Soil Water Content ◽  
Common Scab ◽  
Severe Infection ◽  
Field Capacity ◽  
Streptomyces Scabies ◽  
Screening Tests ◽  
Moisture Meter ◽  
Neutron Moisture

SUMMARYPotato varieties were grown in the field in soil uniformly infected with Streptomyces scabies. In 1969 tubers were severely and evenly infected but in 1971 infection was slight and not uniform. Agreement of varietal ranking with agricultural experience was good in 1969 but poor in 1971.In 1971, plots protected from rainfall after planting were dry enough at the start of tubering for severe infection; covering the plots for a further 6 weeks followed by irrigation to field capacity resulted in good yields of evenly and severely scabbed tubers. Irrigation during this period suppressed scabbing. The results were easily interpreted in relation to fluctuations in soil-water content measured by a neutron moisture-meter.The efficiency of using only one site and the need to reduce variability in scab screening tests are discussed.

Selection and use of representative sites in a large neutron moisture meter network

Soil Research ◽  
1979 ◽  
Vol 17 (2) ◽  
pp. 249 ◽  
Author(s):  
GG Johns
Keyword(s):  
Water Content ◽  
Soil Water ◽  
Root Mean Square ◽  
Mean Square ◽  
Short Term ◽  
Moisture Meter ◽  
Routine Basis ◽  
Neutron Moisture ◽  
Key Sites ◽  
The Relationship

The assessment of the representivity of individual sites in a large neutron moisture meter (NMM) network, and the errors incurred by selecting subsets of various sizes, and using different methods to estimate the full set value from the subsets, is described. Soil water data collected over 13 months from the NMM network (240 sites, divided into eight strata) were analysed to determine the relationship between individual sites and their stratum means. Relationships were assessed using the following four methods: (1) root mean square of the discrepancy; (2) linear regression; (3) quadratic regression; (4) power curve regression. Sites best related to their stratum means were then included in various size subsets, and estimates based on these subsets were compared with the respective full stratum means using 24 months' data. The best estimates of stratum means were obtained by using quadratic regressions and c. eight sites per subset. Using this method, the root mean square discrepancy between estimates of profile water content and observed full stratum means averaged 2.1 mm when the total profile was estimated directly and 2.5 mm when the profile water content was computed as the sum of individual estimates for four arbitrary horizons within the profile. Daily readings of one group of selected subsets indicated the potential of frequent NMM readings at key sites to indicate short-term changes in the soil water content of an area. The performance of the selected subsets has been monitored for a further 12 months as an independent check on their representivity. The root mean square discrepancy of estimates during that period was 2.7 mm. Subsequently only the selected eight sites in each stratum of the field study are being read on a routine basis.

Neutron moisture meter : the dependence of their response on soil parameters

Soil Research ◽  
1986 ◽  
Vol 24 (1) ◽  
pp. 11 ◽  
Author(s):  
DJ Wilson ◽  
AIM Ritchie
Keyword(s):  
Water Content ◽  
Soil Water ◽  
Soil Water Content ◽  
Nuclear Reactor ◽  
Diffusion Theory ◽  
Soil Parameters ◽  
Moisture Meter ◽  
Neutron Moisture ◽  
Theory Calculation ◽  
Neutron Absorption Cross Section

A multigroup diffusion theory calculation based on a nuclear reactor neutronics code is used to determine the response of a neutron moisture meter to changes in soil parameters such as dry soil density, soil water content, thermal neutron absorption cross-section and neutron scattering crosssection. Empirical equations which fit the results can be used to estimate the response at values of the soil parameters other than those used in the calculations. These equations can also be used to estimate the accuracy with which the parameters must be known to achieve a required accuracy in the derived soil water content.

Comparison studies of unsaturated flow below annual and perennial plants

2012 ◽  
Vol 65 (12) ◽  
pp. 2162-2168
Author(s):  
Bill Scott ◽  
Ross Lantzke ◽  
Dave Nicholson ◽  
Paul Findlater
Keyword(s):  
Plant Growth ◽  
Water Content ◽  
Soil Water ◽  
Vertical Profile ◽  
Unsaturated Flow ◽  
Water Movement ◽  
Sandy Soils ◽  
Lambert W Function ◽  
Neutron Moisture ◽  
Soil Water Movement

Values of unsaturated water content determined with neutron moisture measurements (NMM) reveal different water profiles below different plantings. In the extremes, calibration requires a linear and logarithmic response (using the Lambert-W function) along with the normal submersion in a drum of water. Nevertheless a post-calibration with a hydraulic push sampler was used for confirmation. Data were collected at six pastures near the Western Australia coast near Geraldton, with four replicates through the profile. The sites have mostly sandy soils and receive 300–500 mm of rainfall annually. Findings generally showed that, if there was sufficient water, as in 2006, the perennials were able to use the water evenly throughout the vertical profile. Otherwise, with low rainfall, as in 2009, perennials struggle to survive and use less water than the annuals. Modelling of the soil water movement, plant growth and calibration/recalibration is and will be used to get a maximum likehood fit. Clearly, in desert conditions and little or no vegetation, rainfall tends to build up deep in the profile, increase salinity in groundwater, and create waterlogging. Any vegetation is helpful; perennials more so; provided they have sufficient water and are not significantly harvested.

scholarly journals Interaction of soil water and groundwater during the freezing–thawing cycle: field observations and numerical modeling

2021 ◽  
Vol 25 (8) ◽  
pp. 4243-4257
Author(s):  
Hong-Yu Xie ◽  
Xiao-Wei Jiang ◽  
Shu-Cong Tan ◽  
Li Wan ◽  
Xu-Sheng Wang ◽  
...  
Keyword(s):  
Numerical Modeling ◽  
Water Content ◽  
Soil Water ◽  
Water Table ◽  
Groundwater Level ◽  
Water Table Depth ◽  
Field Observations ◽  
Initial Water ◽  
Groundwater Inflow ◽  
The Mean

Abstract. Freezing-induced groundwater-level decline is widely observed in regions with a shallow water table, but many existing studies on freezing-induced groundwater migration do not account for freezing-induced water-level fluctuations. Here, by combining detailed field observations of liquid soil water content and groundwater-level fluctuations at a site in the Ordos Plateau, China, and numerical modeling, we showed that the interaction of soil water and groundwater dynamics was controlled by wintertime atmospheric conditions and topographically driven lateral groundwater inflow. With an initial water table depth of 120 cm and a lateral groundwater inflow rate of 1.03 mm d−1, the observed freezing and thawing-induced fluctuations of soil water content and groundwater level are well reproduced. By calculating the budget of groundwater, the mean upward flux of freezing-induced groundwater loss is 1.46 mm d−1 for 93 d, while the mean flux of thawing-induced groundwater recharge is as high as 3.94 mm d−1 for 32 d. These results could be useful for local water resources management when encountering seasonally frozen soils and for future studies on two- or three-dimensional transient groundwater flow in semi-arid and seasonally frozen regions. By comparing models under a series of conditions, we found the magnitude of freezing-induced groundwater loss decreases with initial water table depth and increases with the rate of groundwater inflow. We also found a fixed-head lower boundary condition would overestimate freezing-induced groundwater migration when the water table depth is shallow. Therefore, an accurate characterization of freezing-induced water table decline is critical to quantifying the contribution of groundwater to hydrological and ecological processes in cold regions.

A field comparison of three neutron moisture meters

1993 ◽  
Vol 33 (1) ◽  
pp. 59 ◽  
Author(s):  
GJ O'Leary ◽  
M Incerti
Keyword(s):  
Water Content ◽  
Soil Water ◽  
Soil Water Content ◽  
Sandy Loam ◽  
Soil Types ◽  
Separate Variable ◽  
Counting Time ◽  
Comparable Performance ◽  
Neutron Moisture ◽  
Use Studies

A study was undertaken to compare 3 neutron moisture meters (NMMs) over a range of counting times on 2 soil types in north-westem 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). The 3 NMMs exhibited different count rates in water, from 242 to 2645 counts per second. It was necessary to increase the counting time of CPN501 to 64 s to achieve a comparable performance to WAL225 at 16 s. 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 (as a separate variable to account for neutron absorbing gradients in the soil profile) 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, with very similar residual mean squares and coefficients of determination. On the grey clay, WAL225 and CPN503 explained 77 and 88% of the variation in soil water content, respectively. CPN501 performed poorly, even with a 64 s counting time, and explained only 52% of the variation when depth was included. When depth was excluded this fell to 25%. On the sandy loam, WAL225 and CPN503 explained 76 and 74%, respectively, of the variation in soil water content. CPN501 again performed poorly with a 64 s counting time, accounting for 65% of the variation when depth was included and 33% with depth excluded. Examples of poor calibrations or none at all in water use studies are discussed and typical errors are demonstrated.

scholarly journals Water use pattern of Pinus tabulaeformis in the semiarid region of Loess Plateau, China

2016 ◽  
Vol 25 (3) ◽  
pp. e077 ◽  
Author(s):  
Shengqi Jian ◽  
Xueli Zhang ◽  
Zening Wu ◽  
Caihong Hu
Keyword(s):  
Water Content ◽  
Soil Water ◽  
Soil Water Content ◽  
Water Use ◽  
Loess Plateau ◽  
Sap Flow ◽  
Pinus Tabulaeformis ◽  
Flow Measurements ◽  
Stand Transpiration ◽  
The Mean

Aim of the study: We analyzed the water-use strategy of P. tabulaeformis and determine the relationships between environmental factors and transpiration rates in the P. tabulaeformis woodlands.Area of study: Loess Plateau region of Northwest China.Material and Methods: Sap flow density of the P. tabulaeformis trees was measured with Granier-type sensors. Stand transpiration was extrapolated from the sap flow measurements of individual trees using the following Granier equation.Main results: The mean sap flow rates of individual P. tabulaeformis trees ranged from 9 L day−1 to 54 L day−1. Photosynthetically active radiation and vapor pressure deficit were the dominant driving factors of transpiration when soil water content was sufficient (soil water content>16%), considering that soil water content is the primary factor of influencing transpiration at the driest month of the year. During the entire growing season, the maximum and minimum daily stand transpiration rates were 2.93 and 0.78 mm day−1, respectively. The mean stand transpiration rate was 1.9 mm day−1, and the total stand transpiration from May to September was 294.1 mm.Research highlights: This study can serve as a basis for detailed analyses of the water physiology and growth of P. tabulaeformis plantation trees for the later application of a climate-driven process model.Keywords: Sap flow; stand transpiration; environmental factor; Pinus tabulaeformis; Loess Plateau.

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