Soil water extraction pattern and water use efficiency of spring canola under growth-stage-based irrigation management.

• Skipping irrigation at the vegetative stage improves water use efficiency in canola. • Soil water extraction depth was similar across irrigation treatments and cultivars. • Canola extracted maximum soil water when stressed during reproductive stage or throughout growing season. The rapid depletion rate of the Ogallala aquifer threatens agriculture sustainability in the U.S. Southern Great Plains (SGP). Adoption of drought tolerant crop with suitable irrigation strategy is critical to improve water use efficiency and sustain crop production in the region. The objective of the study was to assess soil water extraction pattern and water use efficiency of spring canola (Brassica napus L.) under deficit irrigation strategy (DI). Three diverse canola cultivars ('H930', 'H955' and 'L140') were grown under four different irrigation treatments; full-season irrigation (FI), no irrigation at the vegetative stage (VS), no irrigation at the reproductive stage (RS) and dryland (DL). Treatment VS extracted similar amount (20 mm) of total water from planting to harvest as FI in wetter year of 2015. However, VS extracted 10 mm of extra water from soil depth down to 1.6 m until harvest compared to FI in drier year of 2016. As water extraction during reproductive stage in 2016 was almost similar (70 and 67 mm in FI and VS, respectively) in VS and FI, most of the extra water extracted was utilized during vegetative stage when irrigation was skipped in VS. Canola sustained vegetative growth utilizing soil water extraction and efficiently utilized irrigation received during reproductive stage to reduce seasonal evapotranspiration (ET) in VS compared to FI. Treatment RS and DL also reduced seasonal ET, but they reduced average 11 and 13 % oil content compared to FI in 2015 and 2016, respectively. The VS had similar oil content as FI and optimized water use efficiency for biomass (WUE pb), and seed (WUE sy) and oil (WUE oy) yields. Among cultivars, L140 consistently had the greatest WUE pb in both experimental years and 34 and 36 % greater WUE sy and WUE oy in 2016 compared to both H930 and H955, respectively. Adopting spring canola cultivar L140 and skipping irrigation during vegetative stage could maximize water productivity in water deficit conditions of the SGP. [ABSTRACT FROM AUTHOR]