Development of a real time measurement system for tracing water and solute movement in an unsaturated soil column

为实时测量土壤中的含水率和电解液浓度，研制了一种由PC机控制的阻抗测量系统。纵队。在恒温条件下对该系统的效率进行了研究。采用接触式电极和非接触式电极，得到了如下结论：土壤电导率与土壤含水率呈线性关系，土壤电导率与土壤水分电导率和含水率呈线性关系，并给出了理论评价函数，实验证明其有效性是正确的；结论在土柱外表面布置的非接触式电极在100 kHz~1 MHz的频率范围内测量到典型的介电色散现象，本研究采用的阻抗测量系统由于存在漂浮成分而不能很好地测量几MHz以上的频率，介电常数随含水率的增加呈增大趋势，介电常数的增加率随土壤水电解液浓度的增加而减小，介电常数随土壤含水率的增大而增大。利用介电常数和电导建立了估算土壤水分含量和电解质浓度的评价函数，并用该评价函数跟踪了氯化钠溶液在土柱中的非饱和运动，从而说明了用阻抗计实时测量土壤中溶液在土柱中非饱和运动的有效性。

An impedance measurement system controlled by personal computer was developed for a real time measurement of water content and the concentration of electrolyte in a soil. column. The efficiency of this system is studied under a constant temperature condition. Contact-type electrodes and non-contact-type electrodes were used and the following conclusions were obtained.Conclusions obtained by using contact-type electrodes were : suseptance of soil had a linear relationship with water content; conductance of soil had linear relationships with electric conductivity of soil water and water content respectively; the theoretical evaluation function was shown and its efficiency was proved to be right by some experiments; the value of suseptance divided by an angular frequency was determined by water content with no relation to the size of soil particles.Conclusions obtained by using non-contact-type electrodes arranged on an outer surface of a soil column were : typical dielectric dispersion phenomenon was measured at frequencies between 100kHz and 1MHz;the measurement system of this study using impedance meters were not good enough for the measurement over the frequencies of several MHz due to some floating components; dielectric constants showed an increasing tendency with relation to the increase of water content; increasing rate of dielectric constants decreased when the concentration of electrolyte of soil water increased; an evaluation function for estimating water content and the concentration of electrolyte of soil water was developed using dielectric constants and electric conductance and it showed its efficiency for tracing unsaturated movement of NaCl solution through a soil column.Consequently, the efficiency of the real time measurement system using impedance meters for measuring the unsaturated movement of solution through a soil column was shown.