Abstract
The technique of Time Domain Reflectometry (TDR) is important in the evaluation of soil moisture due to being an instantaneous method, which is non-destructive, precise and little dependent on environmental factors. However, researchers have emphasised the need for continuous specific calibration for each soil-management situation. The aim of this work therefore, was to evaluate the response of a portable TDR sensor to soil moisture in a Dystroferric Red Latosol in the Cerrado, under three different systems of soil management and at three different depths in the soil profile. To do this, TDR equipment consisting of two rods, each 0.12 m in length, was used for instantaneous measurement of the volumetric water content of the soil. The depths of 0-0.12, 0.12-0.24 and 0.24-0.36 m were evaluated under three different systems: no-tillage (NT), crop-livestock integration (CLI) and conventional planting (CONV). The response of the TDR sensor varied for both the type of management and for depth. After statistical regression analysis of the data, the values for moisture as a function of the response period of the sensor, and the correlation between moisture by TDR and moisture by the gravimetric method, were highly representative. This demonstrated that the apparatus under evaluation proved to be effective in measuring soil moisture at each depth and under each management system in the specific Latosol under analysis, displaying statistical differences between the treatments.
Highlights
Because of the difficulties involved in determining soil moisture by direct methods, indirect methods are generally used, where moisture is estimated by measuring a related soil attribute (MIRANDA et al, 2007).Among the indirect methods of determining soil moisture, Time Domain Reflectometry (TDR), which relates moisture to the dielectric properties of the soilwater-air environment, has become prominent in recent years, and has been used by several researchers for evaluating humidity and other soil attributes (BROCCA et al, 2009, COPPOLA et al, 2011, PENNA et al, 2013, TOPP; DAVIS; ANNAN, 2003).The TDR sensor quickly and accurately uses the indirect method to determine soil moisture
Based on the hypothesis that moisture transducers are capable of detecting the presence of water in any type of soil, irrespective of the management system, the aim of this study was to evaluate the response of the TDR sensor to moisture in a dystroferric Red Latosol, typical of the Cerrado, under three different management systems, and at three different depths
A trend towards greater compaction can be seen from the values for density throughout the soil profile under the conventional management system, since the three layers of this system remained similar, whereas under the other systems, only the top layers displayed these characteristics
Summary
Because of the difficulties involved in determining soil moisture by direct methods (e.g. gravimetric), indirect methods are generally used, where moisture is estimated by measuring a related soil attribute (MIRANDA et al, 2007).Among the indirect methods of determining soil moisture, Time Domain Reflectometry (TDR), which relates moisture to the dielectric properties of the soilwater-air environment, has become prominent in recent years, and has been used by several researchers for evaluating humidity and other soil attributes (BROCCA et al, 2009, COPPOLA et al, 2011, PENNA et al, 2013, TOPP; DAVIS; ANNAN, 2003).The TDR sensor quickly and accurately uses the indirect method to determine soil moisture. According to Silva and Gervásio (1999), TDR establishes the dielectric constant (ε) of the soil by measuring the return time (t), i.e. the time that an electromagnetic pulse emitted by parallel conductive rods of length L driven into the ground returns to the point of emission. This dielectric permittivity of the soil, which explains the principle of sensor operation, is mainly related to the amount of water present in the substrate, given the range of ε (dimensionless) in the constituent fractions of the soil. Gonçalves et al (2011) demonstrated that these dielectric sensors provide a high correlation with residual soil moisture (θ), indicating a potential for quantitative measurements when well calibrated
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