OPTIMAL FURROW IRRIGATION SCHEDULING UNDER HETEROGENEOUS CONDITIONS

In California, better farm water management practices are needed to me et the increasing water demands by competing water users (industrial, urban, wildlife, etc.), increasing environmental awareness and cost of water. Management can be improved through better irrigation schedulin g and irrigation system designs. In this study, optimal furrow irrigat ion schedules, designs and irrigation adequacy were determined for het erogeneous soil conditions. The seasonal performance between optimal a nd full irrigation was compared. For the bean crop studied, the maximu m return to water was achieved with the irrigation adequacies of 63, 5 9, 54, 49 and 50%, respectively, for irrigation intervals of IO, 12, 1 4, 18, and 21 days. An irrigation interval of 10 days with 63% adequac y gave the global maximum return to water. However, the Natural Resour ce Conservation Service recommended irrigation adequacy for homogeneou s soil condition is 87.5%. For any given irrigation interval, optimal irrigation required less (48-63%) water than full irrigation. This als o reduced bath the deep percolation and runoff losses and caused a 31- 43% increase in the application efficiency. Furthermore, loss in reven ue due to yield rreduction was less than the savings in irrigation cos t, which resulted in higher (32-54%) net return to water under the opt imal irrigation compared with full irrigation. These results indicate that the optimal irrigation strategy hers potential not only for water conservation, but also for reducing non-point source pollution. (C) 1 998 Elsevier Science Ltd All rights reserved.