Precision ag can be based on EC measurement
In addition to EC values separating variations in soil texture, EC has been shown to relate closely to other soil properties used to determine a field’s productivity.
Water-holding capacity/drainage: Droughty areas typically have distinct textural differences from those with excess water; these can be identified using EC. Soils in the middle range of conductivity, which are both medium-textured and have medium water-holding capacity, may be the most productive. Since water holding capacity typically has the single greatest effect on crop yield, this is likely the most valuable use of EC measurements for Virginia.
Cation exchange capacity (CEC): CEC is related to percent of clay and organic matter (O.M.). As the percent of clay and organic matter increase, the CEC also increases. Research bears out the correlation between conductivity and CEC through its relationship to clay.
Depth to claypan or rock outcropping: The response of conductivity to the presence of clay has been used to accurately predict the depth of topsoil over a clay layer or rock outcropping.
Porosity: The greater the total soil porosity, the more easily it conducts electricity. Soil with a high clay content has more total pore space than sandier soils when other soil parameters remain constant.
Salinity: An excess of dissolved salts in the soil is readily detected by electrical conductivity.
Temperature: As temperature decreases to the freezing point of water, soil EC decreases slightly. Below freezing, soil pores become increasingly insulated from each other, and overall soil EC declines rapidly.
Two Sensor Types Can Measure Soil EC
There are two types of sensors commercially available to measure soil EC in the field. Sensor types are contact or non-contact. Measurements by both sensor types have given comparable results.
Contact sensor measurement uses coulters as electrodes to make contact with the soil and to measure the electrical conductivity. In this approach, two to three pairs of coulters are mounted on a toolbar; one pair provides electrical current into the soil (transmitting electrodes) while the other coulters (receiving electrodes) measure the voltage drop between them. Soil EC information is recorded in a data logger along with location information. A global positioning system (GPS) provides the location information to the data logger. The contact sensor is most popular for precision farming applications because large areas can be mapped quickly and it is least susceptible to outside electrical interference. The disadvantage of this system is that it is bulkier than non-contact sensors, and cannot be used in small experimental plots and some small fields.