Spatial variability of hydraulic parameters of a cropped soil using horizontal crosshole ground penetrating radar

• Published in: Vadose zone journal 2025-01, Vol.24 (1)
• Main Authors: Lärm, Lena, Weihermüller, Lutz, Rödder, Jan, van der Kruk, Jan, Vereecken, Harry, Klotzsche, Anja
• Format: Article
• Language: English
• ISSN: 1539-1663; 1539-1663
• DOI: 10.1002/vzj2.20389

Soil hydraulic parameters (SHP) play a crucial role controlling the spatiotemporal distribution of water in the soil–plant continuum and thus affect water availability for crops. To provide reliable information on the SHP at different scales, measurement techniques with a good spatial resolution and low labor costs are required. In this study, we used crosshole ground penetrating radar (GPR)‐derived soil water contents (SWCs) measured along horizontal rhizotubes under a controlled experimental test site cropped with winter wheat to estimate the unimodal and dual‐porosity soil hydraulic characteristics with different soil layer setups. Therefore, sequential inversion of the GPR‐derived SWCs was performed using the hydrological model HYDRUS‐1D, whereby the SWC data were either averaged prior inversion or used in a spatially distributed way. To analyze if the time‐lapse gathered GPR data contain enough information to estimate the SHP, additional synthetic studies were performed increasing the data resolution to daily GPR measurements. The results showed that the time‐lapse data contained enough information to estimate the SHP accurately. Additionally, spatially distributed soil hydraulic characteristics differed from the one estimated based on averaged SWCs derived from spatially distributed GPR data. Finally, we derived spatially resolved SHP, which can be used for 3D process rhizosphere processes and root–soil interaction modeling. 1D and semi‐3D soil hydraulic parameters from ground penetrating radar (GPR) using sequential inversion were derived. The GPR‐derived soil water contents with a hydrological model were combined. Parameters for crop growth studies and their spatial variability were obtained. This study explores the use of ground penetrating radar (GPR) to estimate soil hydraulic parameters (SHP), which are crucial for understanding water distribution in soil and its availability to crops. GPR is used to measure soil water content along horizontal tubes in a winter wheat field. They then used these data to estimate soil hydraulic characteristics using different soil layer and hydraulics setups. The key findings were: inverting time‐lapse GPR data can estimate SHP, the method allowed for the derivation of spatially resolved SHP, and spatially distributed soil hydraulic characteristics differed from those estimated using averaged soil water content. These findings suggest that GPR can be an effective tool for measuring SHP with good spatial resolutio