Measurements in and just below the plant root zone

using principles of soil physics, can be used to estimate recharge. This booklet describes the Zero Flux Plane Method, Methods Based on Darchy's law, and Lysimetry for making such estimates. The work presents the basic concepts of soil water physics that will be referred to in this and other booklets in the series. Another method, the Soil Water Flux Meter, is discussed briefly, but as this is not sufficiently well developed for routine use readers are referred elsewhere for full details. All these methods require that consideration be given to interpolation over time and spatial extrapolation or averaging. A brief discussion of this is given.