Soil fertility and conductivity
The hypothesis that loam soil with fertilizer added will have the highest electrical conductivity has been proven to be true.
The measurements of soil conductivity will only provide some hints as to the amount of minerals present in the soil. It cannot identify the types of minerals that are present. There are many types of conductivity meters available in the market today that are able to measure soil conductivity.
The science fair project may be repeated by adding different types of minerals to the soil samples and subsequently comparing their electrical conductivity.
The experiment may also be modified to measure the effects of other factors on electrical conductivity, eg. by varying the amount of water added, the temperature of the environment, or the pH of the soil.
How to measure soil conductivity? - http://www.ehow.com/how_5901417_measure-soil-conductivity.html
From the soil up – conductivity - http://www.fromthesoilup.com.au/soil/conductivity
Testing the soil conductivity - http://www.eutechinst.com/techtips/tech-tips22.htm