Wenner direct contact method is a method of estimating apparent electrical CONDUCTIVITY (ECa) of agricultural soils in situ. This method can be affected by factors such as quality of electrodes in contact with soil, type of employed electric current, moisture content, clay content and compaction of soil. In this research, the effect of electrode type (rod and plate) and electric current type (direct and alternating) on accuracy of estimating soil ECa has been investigated to design a soil EC mapper. A prototype soil EC meter based on direct contact method has been made. The device assessed by a completely randomized experimental design with factorial layout. The independent variables were soil salinity (five levels), electrodes type (two levels) and current type (two levels).Four soil types with different clay contents from regions around Mashhad city (Khorasan Razavi, Iran) have been used with three replications. The results analyzed with SPSS17 software and validated with 1:1 soils water extract EC’s. Significant difference between electrodes types and electric current types was observed. The correlation coefficients of direct contact measured EC’s with soil water extract EC’s was between 0.94 and 0.99 for all treatments. Based on the results of this research, plate type electrodes and AC current were recommended for the design of tractor rear mounted soil EC mapper.