Time Domain Reflectometry In Soils Research Articles

Spatial Variability Analysis of Within-Field Winter Wheat Nitrogen and Grain Quality Using Canopy Fluorescence Sensor Measurements

Wheat grain protein content (GPC) is a key component when evaluating wheat nutrition. It is also important to determine wheat GPC before harvest for agricultural and food process enterprises in order to optimize the wheat grading process. Wheat GPC across a field is spatially variable due to the inherent variability of soil properties and position in the landscape. The objectives of this field study were: (i) to assess the spatial and temporal variability of wheat nitrogen (N) attributes related to the grain quality of winter wheat production through canopy fluorescence sensor measurements; and (ii) to examine the influence of spatial variability of soil N and moisture across different growth stages on the wheat grain quality. A geostatistical approach was used to analyze data collected from 110 georeferenced locations. In particular, Ordinary Kriging Analysis (OKA) was used to produce maps of wheat GPC, GPC yield, and wheat canopy fluorescence parameters, including simple florescence ratio and Nitrogen Balance Indices (NBI). Soil Nitrate-Nitrogen (NO3-N) content and soil Time Domain Reflectometry (TDR) value in the study field were also interpolated through the OKA method. The fluorescence parameter maps, soil NO3-N and soil TDR maps obtained from the OKA output were compared with the wheat GPC and GPC yield maps in order to assess their relationships. The results of this study indicate that the NBI spatial variability map in the late stage of wheat growth can be used to distinguish areas that produce higher GPC.

Directly Coupled vs. Conventional Time Domain Reflectometry in Soils

Directly Coupled vs. Conventional Time Domain Reflectometry in Soils

Application of dispersion theory to time domain reflectometry in soils : Van Loon, W K P; Perfect, E; Groenevelt, P H; Kay, B D Transport Porous MediaV6, N4, Aug 1991, P391–406

Application of dispersion theory to time domain reflectometry in soils : Van Loon, W K P; Perfect, E; Groenevelt, P H; Kay, B D Transport Porous MediaV6, N4, Aug 1991, P391–406

Application of dispersion theory to time domain reflectometry in soils

With time domain reflectometry (TDR) two dispersive parameters, the dielectric constant, ɛ, and the electrical conductivity, σ can be measured. Both parameters are nonlinear functions of the volume fractions in soil. Because the volume function of water (θw) can change widely in the same soil, empirical equations have been derived to describe these relations. In this paper, a theoretical model is proposed based upon the theory of dispersive behaviour. This is compared with the empirical equations. The agreement between the empirical and theoretical aproaches was highly significant: the ɛ(θw) relation of Topp et al. had a coefficient of determination r2 = 0.996 and the ɛ(θu) relation of Smith and Tice, for the unfrozen water content, θu, at temperatures below 0°C, had an r2 = 0.997. To obtain ɛ(θw) relations, calibration measurements were performed on two soils: Caledon sand and Guelph silt loam. For both soils, an r2 = 0.983 was obtained between the theoretical model and the measured values. The correct relations are especially important at low water contents, where the interaction between water molecules and soil particles is strong.