Effect of irrigation with sea water on soil salinity and yield of oleic sunflower

A field trial was carried out in 2013 and 2014 in a research field near Sari (Iran), to study the effect of irrigation with Caspian Sea water on soil salinity, growth parameters and yield components of oleic sunflower. The experiment was conducted with 4 levels of blending viz. 0% (S0) (fresh water), 15% (S15), 30% (S30) and 45% (S45) mix of sea and fresh water. Soil salinity in the soil profile up to 0-1.0 m increased from 1.1 dS m−1 (before sowing) to 1.4, 2.1, 2.8 and 3.6 dS m−1 for S0, S15, S30 and S45, respectively. In the off-season, soil salinity decreased again to its original level in the control (S0) and to 1.3, 1.8 and 2.7 dS m−1 respectively in S15, S30 and S45, due to rainfall. The corresponding oil yield decreased from 2.6 t ha−1 (S0) to 2.4, 2.0 and 1.5 t ha−1 respectively for S15, S30 and S45. This corresponds to a yield reduction of 10-14% for every 1 dS m−1 increase in soil salinity. The results also indicate that salinity threshold value for oleic sunflower in Sari region is about 1.6 dS m−1. Compared to the control (S0), irrigation with 15% and 30% of sea water had no significant effect on seed yield and irrigation water productivity based on oil yield (IWPoil). For S45, however, seed yield and IWPoil were significantly reduced by 32 and 39% in 2013, and 26 and 34% in 2014. It is concluded that, to irrigate oleic sunflower, 30% Caspian Sea water can be applied for mixing into the irrigating water in the area which has an annual rainfall of 540 mm.