Improving yield, oil content and water productivity of dryland canola by supplementary irrigation and selenium spraying

•Supplementary irrigation in two stages of flowering and grain filling of dryland canola increased yield 2.8 times.•Selenium spraying (1.5 mg L−1) increased canola performance under dryland condition.•Two supplementary irrigation and 1.5 mg L−1 sodium selenate increased water use efficiency two times. Determining the timing of supplementary irrigation in water limited conditions is one approach to reducing drought damage, increasing water productivity, and improving the yield of dryland canola. Selenium spraying may be an appropriate strategy for increasing crop tolerance to drought stress. The aim of this research was to evaluate supplementary irrigation and selenium spraying on the yield and water productivity of two canola cultivars under subtropical dryland conditions. The experiment was a split factorial in a randomized complete block design with three replications conducted during 2016–2018 at Gachsaran Agricultural Research Station, Iran. The main factors consisted of irrigation regimes (no irrigation (I1), supplementary irrigation at flowering stage (I2), grain filling (I3) and flowering + grain filling (I4)), and a sub-factor comprising Hyola 401 (water stress tolerant) and Delgan (less tolerant to water stress) cultivars and selenium spaying from the source of sodium selenate (Na2SeO4) (zero (S0), 1.5 (S1) and 3 (S2) mg L−1). Results showed that the application of supplementary irrigation increased the yield, yield components, oil percentage, harvest index and water productivity. Selenium spraying increased the weight of 1000 seeds and grain yield. Grain yield was increased from 802 kg ha−1 in S0 and I1 treatment up to 2274 kg ha−1 in S2 and I4. The Delgan and Hyola harvest index rose from 19.94 % and 22.1 % in I1 to 29.13 % and 26.99 % in I4, respectively. The highest oil percentage (37.6 %) was observed in the I4 regime, the highest water productivity (0.67 kg m-3) was obtained from I4 and S2 treatments, and the lowest water productivity (0.34 kg m-3) was seen in I1 and S0 treatments. Generally, the results showed that high yielding canola production can be achieved through supplementary irrigation in two stages (flowering and grain filling stages) and by applying 1.5 mg L−1 selenium foliar application in subtropical dryland conditions.