Effect of different levels of water, applied nitrogen and irrigation methods on yield, yield components and IWUE of onion

•The highest onion IWUE was obtained by applying its 75 % and 100 % of water and nitrogen requirements.•Applying 75, 100 and 120 percent of onion water requirements resulted in equal yield.•Utilization of SDI and DI improve IWUE and increase the yield of onion in water stress conditions.•The combined effect of applying SDI and supplying nitrogen mitigates destructivity of deficit irrigation.•Applying nitrogen to crop requirement level increases yield, yield components and IWUE of onion. Different levels of water and nitrogen are considered to have significant effects on yields in arid regions. This paper aims to reveal the effects of levels of water, nitrogen fertilizer and irrigation methods on the yield and yield components of onions. So, the experiments were conducted by surface furrow irrigation (FI), surface drip irrigation (DI) and subsurface drip irrigation (SDI) for two consecutive growing seasons (2014/15–2015/16) in the arid region of Iran. This experiments included four levels of water, i.e., 50 %, (I1), 75 % (I2), 100 % (I3) and 120 % (I4) of crop water requirement. They also contained four levels of applied nitrogen, i.e., 25 % (N1), 50 % (N2), 75 % (N3) and 100 % (N4) of N fertilizer requirement. The treatments were laid out in the form of split-plot with the randomized complete block design, consisting of three replications. Results showed that the amount of irrigation water, nitrogen fertilizer and irrigation method had significant effects with a probability level of 1% on the onion yield and yield components, for both years. The planting year had no significant impact on the yield’s measured parameters. The highest yield and irrigation water use efficiency (IWUE) level were obtained from the (SDI) system (28.42 Mg ha−1 and 5.9 kg m-3 ha−1, respectively) and the lowest performance was obtained from furrow irrigation (19 Mg ha−1 and 2.33 kg m-3 ha−1, respectively). There was a reducing trend for the yield and (IWUE) by reducing nitrogen fertilizer. Also, reducing the amount of irrigation water can minimize the onion bulb yield and increase (IWUE). However, in this regard, no significant effect was observed between (I2) and (I3) treatments. Therefore, according to the results, it is feasible to save 25 % of water usage without a significant reduction in onion yield. However, the decrease in nitrogen can cause a significant reduction in the onion yield. Also, due to the high production potential in (SDI) by reduction of evaporation in an arid