5. Soil-Water Content and Its Measurement

Soil-water content is the basic state characteristic of soil; it expresses the relative quantity of water in the soil. Soil-water content can be expressed as the ratio of water amount and the amount of soil. The most frequently used term is volumetric soil-water content, which is the ratio of water volume and soil volume containing water. Mass soil-water content is expressed as the ratio of water mass and mass of dry soil containing water. Measuring soil-water content is the basic procedure in soil research. Methods for the measurement of soil-water content are briefly described. The basic method is the gravimetric method, a measuring procedure involving only weighing; it is also the reference method of soil-water content measurement, therefore it is described in detail and its weak points (soil—profile destruction and its nature as a discontinuous type of measurement) are discussed. Wide varieties of methods with continuous output are briefly described; neutron method, capacitance method, electrical resistance method, time-domain reflectometry (TDR), frequency-domain reflectometry (FDR), and geophysical and remote-sensing methods.