THE IMPACT ON ELECTRICAL CONDUCTIVITY MEASUREMENT DUE TO SOIL PROFILE PROPERTIES, SHALLOW HYDROLOGIC CONDITIONS, FERTILIZER APPLICATION, AGRICULTURAL TILLAGE, AND THE TYPE OF GEOPHYSICAL METHOD EMPLOYED

Precision agriculture is a growing trend, allowing the right amount of fertilizer, soil amendments, pesticides, herbicides, and tillage effort to be applied to different field areas, thereby optimizing crop yields while reducing input costs. Field crop yield variations are often strongly correlated with spatial soil fertility patterns. The intrinsic fertility of a soil is itself affected by various soil profile properties, such as salinity, organic matter content, cation exchange capacity, grain size distribution, clay mineralogy, claypan/fragipan depth, etc. Apparent soil electrical conductivity (ECa), mapped in situ with geophysical methods, can potentially be used to gauge spatial changes in soil fertility, since it is influenced by these very same properties. However, other factors related more to agricultural field operations also possibly impact ECa, and examples include shallow hydrologic conditions affected by irrigation/drainage (or rainfall), changes in soil nutrient levels from fertilizer application, and alteration of soil density near the surface due to normal tillage operations. The ECa impact of these other factors compared to soil profile properties were investigated primarily through electromagnetic induction (EMI) surveys on a test plot where a series of field condition modifications were undertaken. Here, the average EMI ECa correlated moderately well wit