Quantitative evaluation of soil ion content using an imaginary part model of soil dielectric constant

ABSTRACT: An imaginary part model of soil dielectric constant for predicting the soil salinity status was developed based on a series of relations between dielectric imaginary part and soil bulk conductivity, soil bulk conductivity and soil solution electrical conductivity, and soil solution electrical conductivity and ion contents in soil using pot trials with different soil salinity levels in the 2008 growing season. This model was calibrated and tested with data from the 2009 growing season. The results showed that the inverted values of the total concentration of salt (Sc), Cl−, and Ca2+ at low frequencies (P-band of microwave observations) from the imaginary part model fitted well with the observed values, since root mean square errors (RMSEs) were 0.34 g kg−1, 0.09 g kg−1 and 0.13 g kg−1, respectively, but the inversion effect of Na+ was relatively poor. Moreover, the Sc, Cl−, and Na+ could be well inverted at high frequencies (C-band of microwave observations), since RMSEs were minor, with values of 0.25 g kg−1, 0.02 g kg−1, and 0.15 g kg−1, respectively. The close fit between the observed and inverted values indicated that the present models could be used to estimate soil ion content quickly and reliably under different saline conditions, which, when suitable measures are taken, can be used to reduce the effects of soil salinity on crop growth.

摘要：本研究依托2008年生长季（growing season）不同盐分水平盆栽试验（pot trials），基于土壤介电常数（soil dielectric constant）虚部（imaginary part）与土壤体积电导率（soil bulk conductivity）、土壤体积电导率与土壤溶液电导率（soil solution electrical conductivity）、以及土壤溶液电导率与土壤离子含量间的一系列关联关系，构建了可用于预测土壤盐分状况的土壤介电常数虚部模型。该模型利用2009年生长季的试验数据完成校准与验证。结果显示，在低频微波观测（microwave observations）波段（P-band）下，通过该虚部模型反演得到的盐分总浓度（Sc）、氯离子（Cl⁻）与钙离子（Ca²⁺）的总量与实测值拟合效果优异，对应的均方根误差（root mean square errors, RMSEs）分别为0.34 g kg⁻¹、0.09 g kg⁻¹与0.13 g kg⁻¹，但钠离子（Na⁺）的反演效果相对欠佳。此外，在高频微波观测波段（C-band）下，盐分总浓度、氯离子与钠离子均可实现良好反演，对应的均方根误差分别为0.25 g kg⁻¹、0.02 g kg⁻¹与0.15 g kg⁻¹，误差值均处于较低水平。实测值与反演值间的高度拟合性表明，本模型可在不同盐碱条件下快速且可靠地估算土壤离子含量，若采取适宜调控措施，即可用于减轻土壤盐渍化对作物生长（crop growth）的不利影响。