Strategies to increase barley production and water use efficiency by combining deficit irrigation and nitrogen fertilizer

Iran imported around 1.3 million tons of barley in 2017. Accordingly, conducting researches under low organic matter soils and limited water resources is important to enhance barley products and improve economic conditions. Field experiments were performed to evaluate the effect of different levels of irrigation water (0, 50, 75 and 100% of crop water requirement as main plot) and nitrogen fertilizer (0, 70, 140 and 210 kg ha −1 ; as subplot) on barley (Reyhane 0–3 cv.) growth, agronomic indices and water and nitrogen use efficiency. The results revealed that the barley grain yield dropped by lowering applied water, as the grain yield in 50% irrigation water was around 44% of full irrigation, in both years. Increasing the nitrogen fertilizer to 140 kg ha −1 significantly increased grain yield, while no significant difference was detected between grain yield of 140 kg ha −1 and the highest nitrogen application rate. The maximum water use efficiency was obtained at 75% of full irrigation showing that application of full irrigation did not agronomically increased the grain yield. Nitrogen use efficiency increased by applying more water, while application of nitrogen more than 140 kg ha −1 reduced the nitrogen use efficiency. Furthermore, nitrogen harvest index of 75% indicated that Reyhane 0–3 barley cultivar had the ability to accumulate higher portion of applied N in grain than in straw. Application of 25% deficit irrigation with 140 kg ha −1 nitrogen fertilizer is suggested to obtain the maximum barley production and water use efficiency under semi-arid conditions.