Effects of applied nitrogen fertilizers and irrigation strategies on environmental protection and yield indices of winter wheat and barley in a Mediterranean climate region of Iran

Abstract Because of the excessive use of nitrogen fertilizers, most of the groundwater resources are contaminated in the upstream of the Zayandehrud basin. This study set out to investigate the effect of different levels of water and nitrogen on yield, soil nitrogen, as well as water productivity indices of winter wheat and barley. The experimental treatments were of three nitrogen levels: no nitrogen fertilizer (N0), 50 kg N ha−1 (N1), and 150 kg N ha−1 (N2), as well as two irrigation levels containing deficit irrigation (I1) and full irrigation (I2). Each treatment was repeated three times. Wheat yield for I2 was 5,640 kg ha−1 and for I1 was 3,720 kg ha−1. The yield for barley was 5,620 and 3,850 kg ha−1 for I1 and I2, respectively. The irrigation water productivity (WPi) was increased by 55% for wheat and 83% for barley under deficit irrigation level. We recommend the use of 50 kg ha−1 (instead of 150 kg ha−1), knowing that it reduces the yield and water productivity for wheat by 11.7 and 10.9%, and by 14.5 and 12.6% for barley, respectively. In contrast, the soil nitrogen residual for wheat and barley was reduced by 56.6 and 66.1%, respectively, thus greatly reducing the risk of contamination of groundwater resources.