A water balance trickle irrigation scheduling model

Abstract

In order to conserve water, some form of irrigation scheduling should be used by the farming community. Most irrigation scheduling computer models in the U.S. are 1 dimensional (1 D) water balance models which may not be appropriate for a two dimensional flow (2 D) regime under trickle irrigation. However, the 1 D water balance models have been applied to all forms of irrigation systems from flood, to sprinkler to trickle irrigation. The objective of the research was to develop an irrigation scheduling model that simulates two dimensional water infiltration, drainage, and uptake for a surface line source trickle irrigation system and to compare the results to the simpler 1 D model for a shallow rooted onion crop and a deep rooted chile crop. Two experiments were conducted to evaluate the models. One experiment was conducted during 2006-2007 growing season for a shallow rooted onion crop and the other experiment was conducted for a deep rooted chile crop grown in 1995 and 1996. The 1 D model over estimates seasonal evapotranspiration (Et) compared to the measured values for onions by 20% and for chile by 12%. The 2 D model over estimates seasonal Et compared to the measured values for onion by 5% and for chile by 8%. Therefore, the 2 D model is recommended for scheduling irrigation for trickle irrigated shallow rooted crops. For deep rooted crops both the 1D and 2D models give reasonable results but the 2 D model simulates the seasonal water balance better than the 1 D model.