Direct-push Electrical Conductivity Profiling for Soil Lithology in a Thick Vadose Zone

ZHANG Li~(1,2),LEI Yu-ping~1,ZHENG Li~1,FU Yu-qin~1,Marcia K.SCHULMEISTER~3(1.Center for Agricultural Resources Research,IGDB,Chinese Academy of Sciences,Shijiazhuang 050021,China;2.Graduate School of the Chinese Academy of Sciences,Beijing 100049,China; 3.Earth Science Department,Emporia State University,Emporia,Kansas,USA 66801)

Thick vadose zone;Soil electrical conductivity;Soil lithology

In this paper,we explored the direct-push electrical conductivity measurement for mapping the distribution of soil lithology in a thick vadose zone.The study area is located in the piedmont of the Taihang mountains.The rapid decline of the water table in the piedmont of the Taihang mountains over past several decades has resulted in a thick vadose zone.We employ Geoprobe direct-push technology and a Wenner Array EC probe to collect a series of EC logs and corresponding soil core samples.The core sample analyses indicate that soil moisture of the deep lager is controlled by the corresponding soil lithology. The study site is not saline so that soil lithology is the dominant control on the soil EC.The spatial variation of soil EC measurements reflect the change of soil lithology over space.By performing grain size analyses on the core samples and comparing with the EC logs,we found that EC signals decreased from 100 mS m~(-1) to 30 mS m~(-1) when the sand content of the core samples increased from 12% to 100 %.On the other hand,corresponding to an increase of clay content from 3% to 26%,the corresponding EC could increase from 30 mS m~(-1) to 100 mS m~(-1).The soil EC and sand content are negatively correlated while the soil EC and clay content are positively correlated to each other.This suggests that the direct-push EC logging can be used to infer the soil lithology of a thick vadose zone in this area.