Studies on methods of soil water determination; Research technical completion report project A-019-IDA

The work reported was undertaken with the intent to develop a more reliable instrument initially for remote site operation. A survey of the literature led to the selection of four fields of study: streaming potential, thermal conductivity and specific heat, absorption of infrared radiation by moist soil, and some adaption of the principle of nuclear magnetic resonance. Experimentation revealed that the factors controlling streaming potential were so diverse that isolation of soil moisture or moisture flow variables was not feasible in field applications. Extensive laboratory testing of an original thermal measuring device showed that this principle could be successfully and reliably used in certain ambient temperature ranges. The data also revealed that, when soil is partially frozen at 32 degrees F, information could be derived on the percentage of the soil water in the frozen state, provided the soil moisture content was known. Certain wavelengths in the infrared spectrum are readily absorbed by moisture in the soil. A prototype instrument which utilizes this phenomenon was fabricated. Certain problems in packaging the unit were encountered, but preliminary experimentation assured that this measuring technique shows promise and could be further developed. Nuclear magnetic resonance may be discounted as a means of measuring soil moisture content because of fundamental difficulties