1577 ISSN 1064-2293, Eurasian Soil Science, 2019, Vol. 52, No. 12, pp. 1577–1582. © Pleiades Publishing, Ltd., 2019. Estimating the Soil Water Content Using Electrical Conductivity, Oven Method and Speedy Moisture Tester C. Kurtuluş a , T. Yeken a , and D. Durdağ a, * a Department of Geophysical Engineering, Faculty of Engineering, Kocaeli University, Kocaeli, TR-41380 Turkey *e-mail: dogukan.durdag@kocaeli.edu.tr Received November 27, 2018; revised April 3, 2019; accepted May 22, 2019 Abstract—Soil samples were taken in order to investigate the spatial soil water content changes at 40 points in a field of 675 m 2 located on the old Istanbul-Izmit road in Kocaeli-Turkey. The water content values of soil samples collected were obtained using oven and Speedy Moisture Tester (SMT) in the laboratory to correlate with measured electrical conductivity of soil by electrical resistivity method with a 2-electrode system. The results showed a reasonably good correlation between electrical conductivity and water content. The deter- mination coefficient between the water content and the electrical conductivity found by the oven method (R 2 ≈ 0.8) was higher than that of the SMT (R 2 ≈ 0.6). The correlation between the water content values of oven and SMT is quite affordable with the determination coefficient (R 2 ≈ 0.7). Considering the results obtained from Oven and SMT method, it can be concluded that the resistivity method is also successful in measuring soil water content. It is foreseen that resistivity method can be preferred both because it is easy to use, and large areas are faster and economical in measuring soil water content. Keywords: electrical conductivity, Luvisol, oven method, regression, Speedy Moisture Tester, water content DOI: 10.1134/S1064229319120081 INTRODUCTION Water is the life source of all living things and a spe- cial material for living things. Soil water is necessary for the growth and development of the plant. Soil water content (SWC) defined by Rodríguez-Iturbe and Porp- orato [16] is one of the most important factors for plant growth, microbial decomposition of organic matter of soil, seed germination and plant nutrition. The SWC is also an important parameter that determines the rate of decomposition of the soil organic material, such as soil respiration and soil car- bon attachment rate. Currently, the estimation of SWC can be done in three techniques: (1) in situ mea- surements in the field, (2) remote sensing techniques and (3) soil water balance simulation [21]. In recent decades, much equipment was developed for SWC estimation in an indirect way [6, 24]. So far, many researchers have studied SWC in a variety of ways: Neutron moisture meters [23], cosmic-ray neu- tron probe [20], capacitance sensors [17], tensiome- ters [24], heat pulse sensors [6], fiber optic sensors [7] and GPS [18], Time Domain Reflectometry (TDR) [11, 13, 22] and resistivity meter [1, 5, 26]. Apart from the information on the distribution of the spatial water content of the soil in agricultural engi- neering, the vertical distribution profile of the water is also required. The above-mentioned TDR, remote sensing, cosmic-ray neutron probe: Neutron moisture meters have a depth resolution of only a few centime- ters. Gravimetric or TDR measurements of deeper soil layers are very demanding because they require excava- tion. These methods have limited use in water availabil- ity studies for deeper soil moisture storage and plant growth. With the electrical resistivity measurements of the soil, this problem can be eliminated on a vertical and spatial scale. The cheap, fast and time-saving feature of the resistivity method makes it superior to other meth- ods. The resistivity of rock or soil varies with the water they contain. Since the groundwater has a good con- ductivity, it decreases the resistivity value. In this study, it is aimed to compare the water con- tent of the soil samples determined by oven method and Speedy Moisture Tester with the water content calculated by electrical resistivity method one of the geophysical methods. DESCRIPTION OF STUDY AREA The research area is located along the old Istan- bul–Izmit road in Kocaeli (Fig. 1). The research area is underlain by the Atbasi formation aged from Paleo- cene to lower Eocene. The unit where sandstone and shale, marl and mudstones were intercalated was named as Atbasi formation by Ketin and Gumus [15]. The thickness of the unit varies between 50–500 m. Mechanical drillings in the area showed that 50–70 cm thick soft silty clay with less sand and gravel on the sur- SOIL PHYSICS