Potential use of Caspian Sea water for supplementary irrigation in Northern Iran

Iran's groundwater resources have been over-exploited, often at the expense of deteriorating water and land quality, and there is limited room for expanding its irrigation agriculture. Thus, the possible use of Caspian Sea water, whose salinity is well below that of open seas, for supplementary irrigation has some appeal. The impact of irrigation with diluted Caspian Sea water on the growth and yield of barley and on the characteristics of soil was investigated in field plots and in pot experiments during the 2001–2002 growing season. Three irrigation regimes of well water alone (I₀); Caspian Sea water diluted with well water and used at stem elongation (I₁); and the same diluted sea water used at ear formation (I₂). A rainfed treatment (I_r) was also added to the field experiments. The results of both pot and field experiments show that a 1:1 mixture of Caspian Sea and well water can be used for irrigation without a significant reduction in the growth and yield of barley, provided that it is not applied earlier than the time of ear formation. This would amount to a significantly reduced demand on the limited ground water resources of the region for agricultural use. However, when this mixture was applied at the earlier time of stem elongation, significant yield reduction occurred. All other growth components of barley plants were also adversely affected by this early application of diluted sea water. Soil analysis after harvest showed that the electrical conductivity of the saturation extract had increased significantly in both diluted sea water treatments. This may suggest that the mixing of sea and ground waters at the rates used in these experiments may not be sustainable over a long period of time and soil salinization may occur unless soils are of light texture and sufficient good quality fresh water or winter rain is available to lower the salinity of soil between successive crops. No significant interaction between irrigation salinity and fertiliser treatments was observed.