THE EFFECTS OF SALINITY AT DIFFERENT GROWTH STAGE ON RICE YIELDHassan Ebrahimi Rad, Farshid Aref, M. Rezaei, E. Amiri and M.R. Khaledian
Population growth increases fresh water consumption and decreases water availability. This situation results in increasing pressure on water resources and consequently decreasing in the water portion of agricultural sector. These new conditions led us to find new solutions for utilization of low quality water in agriculture. As other crops, rice production area of northern Iran has met these kinds of problems. A tendency to use saline water in rice production is rising in recent years, but the optimum management of saline waters is still questionable. In order to assess the possibility of brackish water use in rice production and the effects of saline water on different growth stages of rice (Hashemi variety, a popular local variety), a pot research was performed in Rice Research Institute of Iran in Rasht in the North of Iran, under a shelter during 2010 crop season. 4 levels of water salinity i.e. 2, 4, 6, and 8 dsm-1 were applied at 4 different growth stages i.e. tillering (vegetation stage), panicle forming (reproductive stage), heading stage and ripening stage of this local rice variety. Another treatment with fresh water during the whole growth stage was applied to do mean comparison. Saline water was made by using NaCl + CaSO4 (2:1). After 7 days as a period of recovery, salinity treatments were exerted up to 5cm water standing. In order to prevent salt concentration, at the end of each growing stage, pots' soils were washed and irrigation was continued with fresh water. All agricultural practices were done based on usual farmers. After harvesting, plant height, biomass, harvest index, yield and yield components were measured and analyzed, mean comparison was done based on DMRT. Results showed a considerable sensitivity to salinity. Water salinity rate had significant effects on yield, number of filled panicle (p<0.01), biomass and harvest index (p<0.05). Effects of timing of salinity introduction in different rice growth stages on yield, number of filled panicle, biomass and harvest index (p<0.01) and dry weight of straw were statistically significant (p<0.05). The highest yield was obtained from fresh water (no salinity) with 21.5 gr per pot while salinity treatments of 2, 4, 6 and 8 dSm-1 yielded 18.71, 17.79, 14.87 and 12.59 gr per pot, respectively, represented 21, 25, 37, 47% yield losses It can be stated that the panicle formation and tillering stages with 9.40 and 11.81 gr per pot of yield were the most sensitive stages to salinity. The other growth stages including heading and ripping with 20.98 and 21.77 gr per pot, respectively, were the lowest sensitive stages to salinity. Generally, the most sensitive rice processes were reproductive and vegetation stages. The best time of using saline water during the crop season of this Iranian local rice variety seems to be after panicle initiation to the end of ripening application of saline water of any Ec in early growth stage will cause a high yield loss.
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