Optimal furrow irrigation scheduling under heterogeneous conditions

In California, better farm water management practices are needed to meet 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 scheduling and irrigation system designs. In this study, optimal furrow irrigation schedules, designs and irrigation adequacy were determined for heterogeneous soil conditions. The seasonal performance between optimal and full irrigation was compared. For the bean crop studied, the maximum return to water was achieved with the irrigation adequacies of 63, 59, 54, 49 and 50%, respectively, for irrigation intervals of 10, 12, 14, 18, and 21 days. An irrigation interval of 10 days with 63% adequacy gave the global maximum return to water. However, the Natural Resource Conservation Service recommended irrigation adequacy for homogeneous soil condition is 87·5%. For any given irrigation interval, optimal irrigation required less (48–63%) water than full irrigation. This also reduced both the deep percolation and runoff losses and caused a 31–43% increase in the application efficiency. Furthermore, loss in revenue due to yield reduction was less than the savings in irrigation cost, which resulted in higher (32–54%) net return to water under the optimal irrigation compared with full irrigation. These results indicate that the optimal irrigation strategy has potential not only for water conservation, but also for reducing non-point source pollution.