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Determination of Soil Bulk Density with Thermo-Time Domain Reflectometry Sensors

Author:
Liu, Xiaona, Ren, Tusheng, Horton, Robert
Source:
Soil Science Society of America journal 2008 v.72 no.4 pp. 1000-1005
ISSN:
1435-0661
Subject:
bulk density, soil physical properties, time domain reflectometry, sensors, design, measurement, accuracy, equipment performance, nondestructive methods, estimation, thermal analysis, temperature, soil water content, soil water
Abstract:
Surface soil bulk density varies with time and location. In most cases, destructive soil sampling has been used to monitor soil bulk density, ρ Recently the thermo-time domain reflectometry (TDR) technique was shown in principle to be able to estimate ρ Thermo-TDR sensors can measure soil volumetric heat capacity (ρc) and soil water content (θ). Since ρc depends on θ and ρ, measurements of ρc and θ can be used to estimate ρ Previous studies indicated, however, that there were large deviations between thermo-TDR estimates and gravimetric measures of ρ Deviations were attributed mainly to the change of thermo-TDR needle-to-needle spacing during sensor insertion into the soil. The objective of this study was to improve the thermo-TDR sensor design to improve estimation of ρ The ability of three new prototype thermo-TDR sensors, along with an existing thermo-TDR sensor, to estimate ρ was investigated. Evaluation results indicated that a three-needle sensor design with 2-mm needle diameter, 40-mm needle length, and 8-mm needle-to-needle spacing provided the most accurate estimation of soil ρ For this sensor, the RMSEs of ρ estimates compared with gravimetric measures of ρ in laboratory evaluations were 0.055, 0.051, and 0.046 Mg m for a silt loam, a clay loam, and a sand soil, respectively, and was 0.095 Mg m in a field evaluation. In terms of relative error, this specific design was generally within 5% under laboratory conditions and within 10% under field conditions. The improved thermo-TDR sensor provides an opportunity for obtaining accurate, nondestructive, repeated estimates of soil ρ
Agid:
732946