土壤有机物质对土壤介电常数的影响

Effect of soil organic substance on soil dielectric constant

土壤介电常数是开展微波土壤水分和冻融状态的监测的基础,也是植被和积雪的下垫面边界条件,然而目前已有的介电常数研究都没有对高有机质含量的土壤开展系统观测。本文将土壤中的自然有机物质分为腐殖质和植物性残留物两类。采用控制变量实验方法,通过测量5种不同有机质含量的东北黑土和加入不同比例毛白杨碎屑的扁都口草甸土,研究了腐殖质和植物性残留物的对土壤介电常数的影响。结果表明,腐殖质会降低干燥土壤的容重,从而发挥间接作用,使介电常数降低;而对于相同容重下观测的潮湿土壤,腐殖质含量较多的土壤介电常数更大。与Dobson模型的比较显示,在29℃室温下,腐殖质对25%重量含水量潮湿土壤实部的影响在±2左右,虚部能达到1。与腐殖质相比,植物性残留物对风干土壤和潮湿土壤的影响都十分明显。植物性残留物能有效地疏松土壤并代入植物组分的介电特征。当重量含水量为30%时,含毛白杨含量为20%的混合土壤比纯扁都口土壤在实部平均减小3—7左右,虚部减小1—3左右。因此,根据实验观测以及和模型的比较,土壤中的有机物质会改变土壤介电性质,对微波遥感造成影响。

Soil dielectric constant is basic for soil water content and soil froze-thaw status monitoring by microwave remote sensing,and also provides underlying boundary condition for plant and snow.However,present research on soil dielectric constant is lack of systematically measurement on high organic matter soils.This research classified soil natural organic matter substance into two types：humus and plant residue.With rigorous controlled-condition experiment,five black soils in the Northeast China with varied organic matter content and the meadow soil in Biandukou mixed with different content of poplar sawdust were measured to study the dielectric effect of humus and plant residue respectively.Results show that humus can decrease the bulk density of dry soil and decrease soil dielectric constant acting as an indirect mechanism.For wet soil under the same bulk density,the dielectric constant of soil with higher humus content is inclined to be larger.Comparison with Dobson model simulation shows that the impact of humus is around ±2 for real part and can reach 1 for imaginary part for wet soil with 25% gravimetric water content under a room temperature of 29℃.Compared with humus,plant residue influences both dry soil and wet soil significantly.Plant residue can effectively loose soil structure and bring in the dielectric property of a plant component.With gravimetric water content of 30%,the dielectric constant of Biandukou soil mixed with 20% poplar content is 4—7 lower for real part and 1—3 lower for imaginary part than pure Biandukou soil in average.Therefore,the natural organic substance in soil can change soil dielectric constant,and show its impact on microwave remote sensing.