Optimizing Water Use in Irrigation-A Review

In view of the ever increasing demand for water, every effort is directed towards increasing the efficiency of water-use including the optimal use of water for irrigation. An important long term goal of both engineering and agricultural hydrologists is to develop an improved understanding of the hydrologic processes involved in the transport of water from soil into and through vegetation. The process of root water uptake is modelled by a sink term in the equation for flow of water in unsaturated soils. Given the variation in root types, density, and structure with depth into the soil, researchers have used macroscopic models that adopt various functional forms to describe the vertical extraction of soil moisture into the root system. These models have sufficient number of parameters so that they can be fitted to data reasonably well. This paper discusses the physics of root water uptake, root uptake models and moisture extraction studies reported in the literature. Previously published work on performance evaluation of few prominent root uptake models suggests the need for a nonlinear representation of water uptake with depth. In this regard, an empirical model developed by some of the co-authors for nonlinear root uptake parameter is also discussed. Using the nonlinear root uptake model, optimal irrigation schedules may be developed to maximize irrigation water use.