recision farming is a comprehensive approach to farm management and has the following goals and outcomes: increased profitability and sustainability, improved product quality, effective and efficient pest management, energy, water and soil conservation, and surface and ground water protection. In Precision farming, the farm field is broken into “management zones” based on soil pH, yield rates, pest infestation, and other factors that affect crop production. Management decisions are based on the requirements of each zone and precision farming tools (e.g. GPS/GIS) are used to control zone inputs. In contrast, traditional farming methods have used a “whole field” approach where the field is treated as a homogeneous area. Decisions are based on field averages and inputs are applied uniformly across a field in traditional farming. The advantage of precision farming is that management zones with a higher potential for economic return receive more inputs, if needed, than less productive areas. Therefore, the maximum economic return can be achieved for each input. Use of sensors that can sense physical and chemical properties of soil fast, accurate and with low cost is essential for precision farming. Various sensors, including mechanical, acoustic, chemical, magnetic and electrical sensors have been developed; among them sensors which measure apparent electrical conductivity of soil (Ec a ) are very popular. Because in addition to fast, accurate and low cost of measurement, Ec a has strong correlation with some soil properties (such as moisture content, cation concentration and soil texture) that are very effective on crop yield. Electrical sensors that measure soil Ec a are commonly designed based on the Wenner array. In Wenner array, four electrodes are placed into soil while they are arranged in equal intervals. An electric current is sent into the soil from the two outer electrodes and a potential difference between the two inner electrodes is measured. Ratio between the current and potential difference indicates the apparent soil strength (or apparent soil electrical conductivity). In this study, a sensor based on Wenner array for measuring soil apparent electrical conductivity in topsoil layer (0 to 30 cm) was designed and constructed. The Sensor consists of four copper electrodes that can be assembled in four specific rigid cultivator shanks equipped with a narrow blade. The sensor was evaluated under laboratory conditions. Effect of salinity, moisture and soil texture (clay percentage) variation on Ec a was investigated. The tests were conducted in a uniform soil bulk density (1354 kg m -3 ). Effect of four types of texture (clay loam, loam sand, sandy loam and sand), four salinity levels (3.2, 5.2, 7.2 and 9.2 dS m -1 ) and several levels of moisture (from 2.5% (cm 3 cm -3 ) up to the field capacity of