Repeated geophysical measurements in dry and wet soil conditions to describe soil water content variability

ABSTRACT: There is an increasing interest in the application of geophysical surveys to assess the soil water content (SWC) variation in both spatial and temporal scales. In this work, a geophysical survey was carried out at an experimental farm in dry and wet conditions. We determined the SWC data measured with the gravimetric method, apparent electrical conductivity by electromagnetic induction (EMI) and amplitude of Ground Penetrating Radar (GPR) data at different frequencies. Geophysical sensors are an efficient tool for soil mapping at high resolution; however; there is a need to improve the knowledge on their capabilities and limitations under field conditions, especially for GPR. The geophysical survey provides an example of the application of these techniques to evaluate the spatial variability of SWC in two different water conditions. The contribution of geophysical data in understanding the spatial variability of SWC was investigated applying both the traditional analysis and spatial techniques. The results indicated that the geophysical data captured the spatial variation of SWC in non-invasively way especially in dry condition. However, they also showed the complex interplay between factors controlling SWC and geophysical responses and the drawbacks of geophysical sensors under inhomogeneous water conditions. Our findings also highlighted that EMI survey provides the potential to map the SWC variability within a relatively short time. The results obtained in this research are important from the agronomical viewpoint, since they allow increasing efficiency of irrigation practices, which is important in times characterized by climate change.

摘要：近年来，利用地球物理勘探技术评估土壤含水量（soil water content, SWC）的时空变化愈发受到关注。本研究在某试验农场的干旱与湿润工况下开展了地球物理勘探工作。我们获取了通过重量法测得的土壤含水量数据、基于电磁感应（electromagnetic induction, EMI）得到的视电导率数据，以及不同频率下探地雷达（Ground Penetrating Radar, GPR）的振幅数据。地球物理传感器是实现高分辨率土壤制图的高效工具；然而，当前仍需深化对其在野外实地条件下的性能与局限性的认知，针对探地雷达的相关研究尤为不足。本次地球物理勘探展示了上述技术在两种不同水分工况下评估土壤含水量空间变异的应用案例。本研究结合传统分析方法与空间分析技术，探究了地球物理数据在解析土壤含水量空间变异中的作用。研究结果表明，地球物理数据可通过非侵入式方式捕捉土壤含水量的空间变化，在干旱工况下效果尤为显著。但同时也揭示了控制土壤含水量的因素与地球物理响应之间的复杂相互作用，以及非均匀水分条件下地球物理传感器存在的缺陷。本研究结果还凸显出电磁感应勘探具备在相对较短时间内绘制土壤含水量空间分布的潜力。从农艺学视角来看，本研究所得成果具有重要价值，因其可提升灌溉作业的效率，而在当前以气候变化为特征的时代背景下，这一点尤为关键。