Application of Ground-Penetrating Radar and a Combined Penetrometer–Moisture Probe for Evaluating Spatial Distribution of Soil Moisture and Soil Hardness in Coastal and Inland Windbreaks

Kenta Iwasaki,Kazuhiko Masaka,Makoto Tamura,Daisuke Oka,Hirokazu Sato,Ken’Ichirou Kosugi,Yosuke Yamakawa

doi:10.3390/geosciences10060238

Kenta Iwasaki, Kazuhiko Masaka + Show 5 more

Open Access

https://doi.org/10.3390/geosciences10060238

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Abstract

The development of a method to easily investigate the spatial distribution of soil moisture and soil hardness in tree windbreaks is necessary because these windbreaks often decline due to inappropriate soil moisture condition and soil compaction. This research examined the applicability of ground-penetrating radar (GPR) and a combined penetrometer–moisture probe (CPMP) for evaluating the spatial distribution of soil moisture and soil hardness in four windbreaks with different soil characteristics. A GPR-reflecting interface was observed at a less permeable layer in a coastal windbreak and at a depth affected by soil compaction in an inland windbreak with andosol. The spatial distribution of the groundwater table could also be evaluated by examining the attenuation of GPR reflection in a coastal windbreak. In contrast, GPR was not applicable in an inland windbreak with peat because of high soil water content near the soil surface. The CPMP could detect vertical distributions of soil hardness and soil water content regardless of soil type. The CPMP was useful for interpreting GPR profiles, and GPR was useful for interpolating the information about the horizontal distribution of soil moisture and soil hardness between survey points made with the CPMP. Thus, the combination of GPR and a CPMP is ideal for examining the two-dimensional spatial distribution of soil moisture and soil hardness at windbreaks with soils for which both methods are applicable.

Highlights

There are many cases where tree windbreaks have declined due to inappropriate soil moisture condition and soil compaction because they are planted on land without forest soil
Our results suggest that the attenuation depth of ground-penetrating radar (GPR) reflection is a useful indicator of the soil moisture condition in coastal windbreaks with shallow groundwater
Our results show that the combined penetrometer–moisture probe (CPMP) was useful for detecting the groundwater table, less permeable layers, and soil compaction (Figures 4–7)

Summary

Introduction

There are many cases where tree windbreaks have declined due to inappropriate soil moisture condition and soil compaction because they are planted on land without forest soil. Due to deep groundwater levels, cause the dieback of trees at inland windbreaks under dry climates [6], whereas windbreaks can decline in vigor due to shallow groundwater at coastal sand dunes [7,8] and near paddy fields [9] in humid regions. The soil compaction of man-made growth bases in areas where coastal windbreaks were planted after a tsunami in the Tohoku Region, Japan, caused water stagnation in the soil and showed reduced tree growth [12,13]. The development of a method to investigate the spatial distribution of soil moisture and soil hardness at windbreak sites is necessary

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