Use of capacitive sensors with the instantaneous profile method to determine hydraulic conductivity

ABSTRACT Due to the need to monitor soil water tension continuously, the instantaneous profile method is considered laborious, requiring a lot of time, and especially manpower, to set up and maintain. The aim of this work was to evaluate the possibility of using capacitive sensors in place of tensiometers with the instantaneous profile method in an area of the Lower Acaraú Irrigated Perimeter. The experiment was carried out in a Eutrophic Red-Yellow Argisol. The sensors were installed 15, 30, 45 and 60 cm from the surface, and powered by photovoltaic panels, using a power manager to charge the battery and to supply power at night. Records from the capacitive sensors were collected every five minutes and stored on a data acquisition board. With the simultaneous measurement of soil moisture obtained by the sensors, and the total soil water potential from the soil water retention curve, it was possible to determine the hydraulic conductivity as a function of the volumetric water content for each period using the Richards equation. At the end of the experiment, the advantage of using capacitive sensors with the instantaneous profile method was confirmed as an alternative to using a tensiometer. The main advantages of using capacitive sensors were to make the method less laborious and to allow moisture readings at higher tensions in soils of a sandy texture.

摘要：由于需持续监测土壤水张力，瞬时剖面法（instantaneous profile method）被认为操作繁琐，搭建与维护过程需耗费大量时间，尤其需要投入大量人力。本研究旨在评估在下阿卡拉乌灌溉区（Lower Acaraú Irrigated Perimeter）某区域内，使用电容式传感器（capacitive sensors）替代张力计（tensiometers）配合瞬时剖面法开展监测的可行性。实验在富养红黄色黏磐始成土（Eutrophic Red-Yellow Argisol）中开展。传感器分别布置于距地表15、30、45及60 cm深度处，由光伏板供电，并通过电源管理器为蓄电池充电以保障夜间供电。电容式传感器的采集数据每5分钟记录一次，并存储于数据采集板（data acquisition board）中。结合传感器测得的土壤含水率同步数据与通过土壤水分特征曲线（soil water retention curve）得到的总土壤水势，可利用理查兹方程（Richards equation）计算得到各时段下与体积含水率相关的水力传导度。实验结束后，证实了将电容式传感器与瞬时剖面法结合作为张力计替代方案的优势。电容式传感器的核心优势在于降低了该方法的操作复杂度，且可在砂质土壤的更高水张力条件下获取含水率读数。