Abstract

Soil properties are often non-uniformly distributed within the fields. The key soil characteristics (moisture, salinity, acidity, texture, total fertility) vary across the field and dictate variable rates of agricultural inputs. Geophysical methods of Electrical Resistivity (ER) or Conductivity (EC) have been used to map soil properties since 1930 in the USA and since 1960 in Europe, as summarized in Allred et al. [1] and Pozdnyakov [2]. Methods of Direct Current (DC) such as four-electrode probe mapping and Vertical Electrical Sounding (VES) provide actual values of ER at multiple depths but slower than methods of Electromagnetic Induction (EMI). However, the depth of penetration and ER values measured with EMI methods varies depending on soil type and field condition. Farm fields were mapped with AEMP-14 in Rostov, Russia and Montrose, IA, USA, in 2021; ER at low frequencies (15-25kHz) correlated with available water at 50-70cm depth. Electrical resistivity at higher frequencies (60kHz) correlated with pH at a 10-20 cm depth. A Methodic of Calibrating EMI (AEMP-14) measurements with DC VES (Land Mapper) at a few locations is proposed to quantify ER values at multiple depths in outlined areas.

Keywords: Vertical electrical sounding; Agronomy; Soil; AEMP-14; Land mapper