Investigation of Simultaneous effect of periodic water stress and salinity of Caspian Sea water on cotton yield

Water is undoubtedly one of the factors of productivity and reducing water consuming reduces the yield. But the decrease in yield due to water stress is inevitable. Because of limited water resources in Iran, deficit irrigation and water stress on crops are inevitable. Also in some regions, saline water is being used for irrigation. The saline lands of Iran are about 44.5 million hectares with various salinity and alkalinity, which are 27% of the area of the country and they are mainly located in the central plateau, southern coasts of Iran and the Caspian Sea coasts. Saline water has been successfully used for irrigating the crops such as cotton, wheat, barley and sugar beet. Deficit Irrigation (DI) is a method in irrigation management and an engineering technique which is used to optimize the yield in water scarcity and increasing water efficiency. In this method, some irrigation events which have less effect on productivity could be omitted or the volume of water in each irrigation event could be reduced. The salinity of water resources and soils in Iran is one of the problems barricades the effective application of these resources in agriculture. However, it has been tried to use unconventional water resources such as Caspian Sea to ease water shortage, especially in droughts in Northern provinces. Various reports have been presented on the effect of salinity on cotton. Some research expressed that irrigating by 6,000 mg of salt per liter had acceptable yield without any bad effect on the quality of cotton fiber and seeds. In this study, the simultaneous effects of periodic water stress and salinity stress due to using the Caspian Sea water on cotton yield was investigated, which was carried out in the agricultural research farm of Gorgan University of Agricultural Sciences and Natural Resources. This research is based on a factorial experiment in completely block design (CRD) including 20 treatments and 3 replicates in the farm of Gorgan University of Agriculture on spring 2012. Three cotton seed of Golestan variety were planted in lysimeters with the diameter of 35 cm and an average height of 70 cm. The distance between Lysimeters was one meter. To measure the cotton water requirement, pan (class A) was used. Also the effective rain during the cultivation was measured with a rain gauge which was installed near the research farm. Periodic water stress in four stages (Initial, early stage of development, the second stage of development, midseason) was applied and the salinity stress was performed at 5 levels (0% 25%, 50%, 75% and 100% mixture of Caspian sea water with ordinary water) .The Salinity was 0.7, 4.1, 11.1, 18.11, 25.1 (dS/m), respectively.
Results of this study showed that the effect of Periodic water stress and salinity from Caspian Sea water on Plant's height, boll weight, seed cotton yield was significant at the 1% level. But its effect on boll number was significant at 5% level. Also, the interaction of water stress and salinity on boll weight, seed cotton yield and plant height was significant at 1% level but the interaction of water stress and salinity at the boll number was not significant. Comparison of mean of the salinity stress in soil was done at each level of water stresses in order to reach a better understanding of the interactions. Depths of the measurements were 0-10 cm and 10-20 cm from the soil surface. By increasing salinity of irrigating water and applying water stress, soil salinity was increased. The highest soil salinity among the different level was occurred in S5 level. Because the soil salinity was increased in all treatments which were irrigated by saline water, considering leaching water in water events is necessary.
Periodic water stress also increased the salinity in soil. This increase was higher in the midseason period due to the length of this period.
By the results, the cotton yield was generally decreased by increasing salinity of irrigating water. The interaction of periodic water stress and salinity had significant effects on the cotton yield. But at the level of 25% mix of Caspian Sea water with ordinary water, in the early stage of crop development, the difference of results were lower than other treatments. So this planning could be an appropriate choice for Northern provinces of Iran in droughts and limitation of water resources.