Direct comparisons of four irrigation systems on a commercial rice farm: Irrigation water use efficiencies and water dynamics

This two-year field study compared the industry-standard rice (Oryza sativa L.) irrigation practice, a continuous-flood delivered using cascade distribution (CASC), to two related levee-based systems (multiple-inlet rice flood distribution (MIRI) and MIRI plus alternate wetting-drying flood management (AWD)) and one furrow-irrigated with end-blocking (ROW) system. Seasonal applied irrigation, soil volumetric water holding content, water depth, grain yield and irrigation water use efficiency (IWUE) were determined for sixteen 16-ha commercial rice fields sown using the same hybrid each year. Also, runoff from one field for each system was measured each year. Average seasonal irrigation applications were 824 ± 197 mm for CASC, 641 ± 165 mm for MIRI, 696 ± 181 mm for AWD and 631 ± 125 mm for ROW. Although a minimum of two AWD dry-down cycles were performed each year and runoff was the least from MIRI (5% runoff) and AWD (3% runoff), ROW (13% runoff) was the only system to receive less irrigation (p = 0.0314) than CASC (14% runoff). In terms of grain yield, only the ROW fields, with an average yield of 8890 ± 417 kg ha⁻¹, differed (p = 0.0107) from CASC (9991 ± 751 kg ha⁻¹). This reduction in ROW yield was due primarily to herbicide injury in 2018 and resulted in average irrigation water use efficiency (IWUE) values that were not different between irrigation treatments (p > 0.05). Taken together, ROW with end-blocking (a) proved to be a more consistent method of water conservation than MIRI and AWD under field conditions complicated by variable soil textures, and (b) lends itself to automation as the ROW fields were irrigated regularly, on a three-to-four-day schedule, rather than depending on human judgement to decide when to irrigate as was required for CASC, MIRI and AWD.