The response of the shallow portion of the ground (vadose zone) and of earth structures is affected by the interaction with the atmosphere. Very frequently, the ground surface is covered by vegetation and, as a result, transpiration plays a major role in ground–atmosphere​ interaction. The soil and the plant form a continuous hydraulic system that needs to be characterised to model the ‘boundary condition’ of the geotechnical water flow problem. Water flow in soil and plant takes place because of gradients in hydraulic head triggered by the water tension (negative water pressure) generated in the leaf stomata. To study the response of the soil–plant continuum, water tension needs to be measured not only in the soil but also in the plant (in addition to the water content in the soil). This paper first evaluates three instruments that can be used to measure xylem water tension, i.e. the High-Capacity Tensiometer (HCT) and the Thermocouple Psychrometer (TP) for continuous non-destructive measurement on the stem, and the Pressure Chamber (PC) for discontinuous destructive measurement on the leaves. Experimental procedures are presented and critically discussed, including data quality control and instrument calibration, accuracy, and precision. The performance of these three instruments is evaluated in terms of measurement precision and measurement accuracy via cross-validation. The paper then addresses the problem of monitoring soil suction (pore-water tension) and water content using a second generation profile probe (fully encapsulated) and the use of Electrical Resistivity Tomography (ERT) for coarse characterisation of water content spatial distribution to support the design of spatial configuration of suction and water content sensors.

地面浅部（渗流带）和地球结构的响应受到与大气相互作用的影响。地表经常被植被覆盖，因此蒸腾作用在地气相互作用中起着重要作用。土壤和植物形成一个连续的水力系统，需要对其进行表征以模拟岩土水流问题的“边界条件”。由于叶气孔中产生的水张力（负水压）引发的水头梯度，土壤和植物中的水流发生。为了研究土壤-植物连续体的响应，不仅需要测量土壤中的水分张力，还需要测量植物中的水分张力（除了土壤中的水分含量）。本文首先评估了三种可用于测量木质部水分张力的仪器，即用于对茎杆进行连续无损测量的高容量张力计 (HCT) 和热电偶湿度计 (TP)，以及用于测量木质部水分张力的压力室 (PC)。对叶子进行不连续破坏性测量。介绍并批判性地讨论了实验程序，包括数据质量控制和仪器校准、准确性和精密度。通过交叉验证从测量精度和测量准确度方面评估这三种仪器的性能。