Winter canola water use response under dormant and growth stage based irrigation strategies

Declining Ogallala Aquifer in the semiarid southern High Plains (SHP) is threatening highly productive irrigated agriculture. Winter canola ( Brassica napus L.) requires less irrigation water than traditional crops. Identifying irrigation strategy that skips irrigation at less critical growth stage or refills soil profile during dormant period to further reduce irrigation inputs may improve sustainability of Ogallala Aquifer. A field study was conducted at Clovis, NM during 2017–18 and 2018–19 seasons using two cultivars (cvs. Hekip and Riley) to assess soil water extraction patterns (SWE), and water productivity (WP) under various irrigation regimes. Main plot treatments consisted of with (DPI) and without (NDPI) dormant period irrigation, while growth stage-based irrigations included FI (irrigation throughout the season), VS (no irrigation before first blossom), RS (no irrigation after first blossom), and RD (no irrigation after establishment) as the sub-plot treatments. The DPI significantly increased SWE, consumptive water use, biomass (BY) and seed yield (SY). However, extra water extracted in DPI did not improve WP BY & SY . Irrigation restrictions during any part of the growing season were detrimental as compared to continuous irrigation. However, restricting irrigation to the first blossom stage was less impactful, as the VS treatment had higher yields and WPs than the RS and RD treatment. There was marginal effect of cultivar-type on SWE, and WPs. To summarize, winter canola was able to tap into stored dormant irrigation but was not effectively used in yield formation. Growers with limited irrigation can implement in-season VS regime without significant yield loss or WP. • Winter canola accessed soil water stored with dormant period irrigation throughout the growing season. • Vegetative growth stage was less sensitive to skipping irrigation than reproductive growth stage in winter canola. • None of the irrigation strategies improved water productivity for biomass or seed production in winter canola. • If irrigation is limited, farmers should use it after flowering started in winter canola.