Abstract: A miniature, low power consuming, density gage utilizing extremely small artificial and naturally found radioactive sources. The gage employs a unique method of compensating for the gamma attenuation coefficient in different materials such as soils to provide a very simple but accurate and effective moisture gage. A single source emits radiation beams, one through a control sample of the material and at least one beam through a zone of the material where moisture content is to be determined. The apparatus may optionally be employed to control a crop irrigation system to maintain moisture within the comfort zone of the plants growing in the soil. The invention also may be used for measuring moisture content in several discrete zones of the material.