Calibration and application of Aquaflex TDT soil water probes to measure the soil water dynamics of agricultural topsoil in Southwest Germany

Publication Type

Journal contribution (peer reviewed)

Authors

Poltoradnev, M., Ingwersen, J., Streck, T.

Year of publication

2015

Published in

Journal of Irrigation and Drainage Engineering

Band/Volume

141/6

DOI

10.1061/(ASCE)IR.1943-4774.0000838

<p>Soil water plays a key role in crop growth and yield formation. A sustainable irrigation management depends on a reliable soil water monitoring. The present study was conducted to derive site-specific and pedotransfer calibrations for Aquaflex time domain transmission (TDT) soil water sensors and to test their performance under field conditions. In spring 2009, two soil moisture networks were installed in the Kraichgau region and in the Swabian Alb, southwest Germany. Each network consists of 21 stations, each equipped among others with an Aquaflex TDT sensor installed 15-cm-deep in the soil. At each station, soil samples were taken and analyzed for the gravimetric soil water content, bulk density, soil texture, electrical conductivity, pH, and organic nitrogen and carbon content. The factory calibration delivered highly biased soil water contents [<span style="color: inherit;"></span><span><span style="width: 8.854em; display: inline-block;"><span style="display: inline-block; position: relative; width: 7.361em; height: 0px; font-size: 120%;"><span style="position: absolute; clip: rect(1.875em, 1000em, 3.008em, -1000em); top: -2.778em; left: 0em;"><span><span><span style="font-family: MathJax_Main; padding-left: 0.333em; padding-right: 0.333em;">&sim;</span><span style="font-family: MathJax_Main;">&minus;</span><span style="font-family: MathJax_Main;">8.0</span><span style="font-family: MathJax_Main;">&thinsp;</span><span style="font-family: MathJax_Main;">&thinsp;</span><span style="font-family: MathJax_Main; padding-left: 0.167em;">Volume</span></span></span><span style="display: inline-block; width: 0px; height: 2.778em;"></span></span></span><span style="border-left: 0em solid; display: inline-block; overflow: hidden; width: 0px; height: 1.026em; vertical-align: -0.11em;"></span></span></span> (Vol.) %]. The root mean square errors (RMSEs) were high, reaching on average 8.3 and 12.6&nbsp;Vol.% in Kraichgau and Swabian Alb, respectively. The RMSEs of pedotransfer calibrations declined to 3.7&nbsp;Vol.% in Kraichgau and to 3.4&nbsp;Vol.% in Swabian Alb. In both regions, the slope of the calibration curve was affected by soil bulk density. High-leverage independent variables affecting the intercept were electrical conductivity in Kraichgau and silt fraction in Swabian Alb. Site-specific calibrations performed best. On average, the RMSE in Kraichgau was 3.0&nbsp;Vol.%, in Swabian Alb 1.9&nbsp;Vol.%. The pedotransfer-based approach proposed in the present study is a good compromise between labour effort and accuracy for soil landscapes with similar texture and properties.<span><br /></span><span></span></p>