The Soil Solution Phase

Biological production from soil, either as forest products or agricultural crops, is influenced primarily by water availability. This, in turn, depends on the soil properties and the water content of the soil. Water content measurement techniques are often classified as either direct or indirect. Among the various remote sensing approaches to measuring soil water content, active microwave remote sensing instruments have a unique advantage. The main application of the electromagnetic induction method is probably found in studies where soil water content changes need to be monitored over large areas with relatively constant soil solute contents. The number of tubes required to control variance in water content measurement is a complex matter. Variance arises from four sources: random variation in neutron emission from the source, counting error, variation in water content across the site, and calibration error. The oven-drying method is a commonly used and convenient method to obtain a good estimate of soil water content.