Electrical Properties of Soils - Electro-Horticulture - page 38

Electrical resistivity is the most variable of all geophysical properties of rocks because of
theenormousrangeofvaluesthatarepossible,rangingasmuchas10ordersofmagnitude.
The next chart illustrates in a general way how the resistivities of rock groups compare to
each other.
Resistivities of Various Rock Groups
Source: University of British Columbia
As shown in the chart, note how each vertical bar is a 10 times increase or decrease
in conductivity or resistivity. Considering that the growth of plants is affected by
electrochemical soil interactions (See Chapter 6 ) , the natural occurrence of different types
of rocks and their presence in the soil may have a huge influence on soil fertility.
Composed mostly of silicate minerals, soils and rocks are essentially insulators with the
followingexceptions: magnetite, specularhematite, carbon,graphite,pyriteandpyrrhotite.
Since most rocks are resistive in nature, the electrical conductivity of soils is primarily due
to the presence of electrolytes 1 and carbon itself. As stated before, the conductivity of soil
depends on a number of factors:
• Porosity
• Hydraulic permeabilit y 2
• Moisture content