A water-balance drip-irrigation scheduling model

Abstract

To conserve water, some form of irrigation scheduling should be used by the farming community. Most irrigation scheduling computer models in the United States are one-dimensional water balance models that may not be appropriate for a two-dimensional flow regime under drip irrigation. However, the one-dimensional water balance models have been applied to all forms of irrigation systems, from flood, to sprinkler to drip 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-drip irrigation system and to compare the results to the simpler one-dimensional model for a shallow-rooted onion crop and a deep-rooted chile pepper (Capsicum annuum) crop. Two experiments were conducted to evaluate the models. One was conducted during the 2006–2007 growing season for a shallow-rooted onion (Allium cepa L.) crop and the other for a deep-rooted chile pepper crop grown in 1995 and 1996. The one-dimensional model overestimates seasonal evapotranspiration (Et) compared to the measured values for onions by 20% and for chile by 12%. The two-dimensional model overestimates seasonal Et compared to the measured values for onion by 5% and for chile by 8%. Therefore, the two-dimensional model is recommended for scheduling irrigation for drip-irrigated shallow-rooted crops. For deep-rooted crops, both the one-dimensional and two-dimensional models give reasonable results, but the two-dimensional model simulates the seasonal water balance better than the one-dimensional model.