容重及含水率对土壤电导率的影响研究

Influence of bulk density and water content on soil electrical conductivity

土壤电导率能够间接反映田间养分或盐分含量,通过监测土壤电导率可以掌握土壤养分或盐分运移和利用情况。本文通过2种土壤容重、5种含水率条件下土柱入渗试验,利用5TE传感器对土壤体积含水率、体积电导率、温度等参数进行连续监测,分析容重及含水率对土壤电导率的影响。结果表明:在入渗过程中,含水率和电导率均先增大后逐渐减小,最后趋于平缓;电导率开始减小的时间较含水率开始减小的时间略有提前;当体积含水率一定时,孔隙水电导率随体积电导率的增加基本呈线性增加;随含水率的增大,孔隙水电导率随体积水电导率增大的速率变慢;当体积电导率一定时,随着含水率的增加,孔隙水电导率逐渐减小,容重为1.35 g·cm^(-3)时减幅为9.52%~55.51%,容重为1.3 g·cm^(-3)时减幅为9.72%~54.62%;孔隙水电导率一定时,体积电导率随含水率的增加而增大,容重为1.35 g·cm^(-3)时增幅为10.51%~124.75%,容重为1.3 g·cm^(-3)时增幅为10.76%~120.35%。对于2种容重情况,相同含水率下孔隙水电导率与体积电导率呈线性关系;在孔隙水电导率相同时,体积电导率随着容重的减小而略呈上升趋势,与容重1.35 g·cm^(-3)处理相比,容重1.3 g·cm^(-3)处理中含水率24%、25%、26%情况下的体积电导率分别提高1.95%、2.47%、1.44%。在入渗总水量有限时,土壤水含盐量随体积含水率的变化经历4个阶段,入渗过程中随着体积含水率持续增加,分为无盐溶出、含盐量快速增加和含盐量减小3个阶段,以及水分再分布过程中的体积含水率与含盐量均减小阶段;在第2个阶段末各工况溶出的盐量达到最大值,容重1.35 g·cm^(-3)处理中,平均体积含水率为20%、22.5%、25%、28%、31%的工况达到盐量最大值,分别为3.54、4.95、7.17、31.73、11.85 mS·cm^(-1);第4个阶段末达到设计的平均体积含水率。孔隙水电导率与体积电导率呈线性关系,其斜率随着含水率的增加而减小,是含水率的二次函数;可采用含水率和孔隙水电导率的乘积反映土壤溶液盐分含量。

Soil electrical conductivity can indirectly reflect the nutrient or salt content in the field.Monitoring the soil electrical conductivity can help understand the transport and utilization of soil nutrients and salt.In this study,through the soil column infiltration test under the conditions of 2 soil bulk densities and 5 water contents,the 5TE sensor was used to continuously monitor soil volumetric water content,volume conductivity,temperature,and other parameters,and analyze the influence of bulk density and water content on soil conductivity.The results showed that both water content and conductivity first increased,then gradually decreased,and finally tended to be flat during the infiltration process.The time when the conductivity began to decrease was slightly earlier than the time when the water content began to decrease.When the volumetric water content was constant,the conductivity of pore water increases linearly with the increase of volumetric conductivity.With the increase of water content,the increase rate of pore water conductivity with volume water conductivity was slower.When the volume conductivity was constant,the conductivity of pore water decreased gradually with the increase of water content,and the decrease range was 9.52%~55.51%when the bulk density was 1.35 g·cm^(-3),and the decrease range was 9.72%~54.62%when the bulk density was 1.3 g·cm^(-3).When the conductivity of pore water was constant,the volume conductivity increased with the increase of water content,the increase was 10.51%~124.75%when the bulk density was 1.35 g·cm^(-3),and the increase was 10.76%~120.35%when the bulk density was 1.3 g·cm^(-3).Under the same water content,for the two bulk density cases,the measured pore water conductivity had a linear relationship with the volume conductivity.When the pore water conductivity was the same,the volume conductivity increased slightly with the decrease of the bulk density.When the water content was 24%,25%,and 26%,compared with the volume conductivity when the bulk density was 1.35 g·cm^(-3),the bulk conductivity increased by 1.95%,2.47%,and 1.44%when the bulk density was 1.3 g·cm^(-3),respectively.When the total infiltration water was limited,the change of soil water salinity with volumetric water content experienced four stages.With the continuous increase of volumetric water content during infiltration,the soil water salinity could be divided into three stages:salt-free dissolution,rapid increase of salt content and decrease of salt content,and the stage of decrease of both volumetric water content and salt content during water redistribution.At the end of the second stage,the amount of dissolved salt in each working condition reached the maximum value.When the bulk density was 1.35 g·cm^(-3) and the average volumetric water were 20%,22.5%,25%,28%and 31%,the maximum salt content were 3.54,4.95,7.17,31.73 and 11.85 mS·cm^(-1),respectively.At the end of the fourth stage,the designed average volumetric moisture content was achieved.The pore water conductivity had a linear relationship with the volume conductivity,and its slope decreased with the increase of water content,which was a quadratic function of water content.The product of water content and pore water conductivity could be used to reflect the salt content of soil solution.