Effect of Water Management on Efficiency of Preflood Nitrogen Applications in a Drill-Seeded, Delayed Flood Rice Production System.

Dwindling water sources for irrigation water and concerns about greenhouse gases have resulted in alternate water management practices in rice production. These practices may enhance efficient use of water but also have potential to decrease nitrogen use efficiency (NUE). The objective of this study was to examine the influence of different water management systems on NUE. A randomized complete block design was utilized to evaluate NUE of the rice variety ‘Presidio’ and the rice hybrid ‘CLXL745’ under four water management systems in a two-year field study. Treatments were replicated four times. The water management systems examined were continuous flooding, straighthead, intermittent and semi-aerobic. Nitrogen was applied at rates 0 and 135 kg ha^-1. Rice NUE was determined by using the difference method. Yield of CLXL745 pooled across differing water management systems was significantly greater than Presidio. Yields from plots managed under continuous flooding were greater than semi-aerobic water management but similar to intermittent and straighthead water management systems. The NUE for continuous, straighthead, intermittent and semi-aerobic rice management systems were 78, 70, 57 and 46%, respectively. NUE of continuous flood rice was significantly higher than straighthead and semi-aerobic but comparable to intermittent. The NUE of CLXL745 (71%) was significantly higher than Presidio (54%) across all water management systems. Results from this study showed that yield and NUE from conventional flooding system is superior to semi-aerobic and comparable to intermittent flooding systems.