CONTROL OF IRRIGATION AMOUNTS USING VELOCITY AND POSITION OF WETTING FRONT

A new approach for the estimation and control of the quantity of water applied in an irrigation is presented in which irrigation is stopped when the wetting front reaches a critical depth, Z(L). An expression f or calculating the critical depth Z(L) was developed. A major paramete r in this expression is the velocity of advance of the wetting front, V, which was shown to be directly related to the application rate, IR, and inversely related to the initial soil water content, theta(i). A depth probe (patent pending) was designed, constructed and tested for the purpose of monitoring the position of the wetting front during inf iltration and redistribution and for computing the value of V. Equatio ns developed for relating the velocity of advance of the wetting front to theta(i), as well as for estimating the value of the critical dept h Z(L) were successfully tested under conditions of uniform distributi on of the initial soil water content. An iterative learning process wh ich utilizes the real time output from the depth probe during each irr igation and is therefore capable of handling realistic field condition s where nonuniformity is the rule is presented. The acquired informati on is used to estimate a critical depth of the wetting front, Z(L), fo r a planned final wetted depth, Z(F), during each irrigation. This pro cess is incorporated in the depth probe and is used to stop irrigation and thus control the quantity of water applied.