Investigating irrigation scheduling for rice using variable rate irrigation

Because almost all US rice is produced with continuous flood irrigation, little information addresses irrigation scheduling for rice; however, successful production without a continuous flood will require timely irrigation. A field study conducted at the University of Missouri Fisher Delta Research Center Marsh Farm during the 2013 and 2014 growing seasons investigated irrigation scheduling for sprinkler irrigated rice. Two irrigation timings were based on management allowed depletion (MAD) (MAD1: 10 mm application at a 12 mm estimated soil water deficit (SWD); MAD2: 15 mm application at a 19 mm estimated SWD). For each MAD treatment, three VRI settings represented 75, 100, and 125% of the target applications. Seven fewer irrigations were applied to MAD2 plots in 2013 and eleven fewer in 2014 but larger applications resulted in similar total application amounts. Neither treatment main effect was significant for yield in 2013, but there was a significant interaction, with differences among the % application treatments for MAD2. The % application main effect was significant for irrigation water use efficiency and there was a significant interaction. Yields were lower in 2014 than in 2013, which was expected given the late planting and soil compaction that resulted from land grading. Soil moisture data were inconsistent, and variability among the sensors led to few significant differences. Yield was significantly greater than the field average for only one treatment combination (MAD1 - 100%) and significantly lower for two (MAD2 - 75, 100%). Irrigation water use efficiency of two of the treatment combinations was significantly greater than the field average (MAD1 - 75%, MAD2 - 75%) while two were significantly lower (MAD1 - 125%, MAD2 - 125%). While the findings suggest that sprinkler irrigated rice performed equally well under a range of irrigation management, additional research is needed to validate these trends and develop improved guidelines for producers.