Determination Of Dilution Point For Saline Irrigation Based On Physiological Response Of Two Okra Cultivars Under Salt Stress Followed By Re-watering

Salt stress is one of the major limitations in the advancement of agriculture in humid, arid, and semiarid regions in the world. Each year, about 40,000 ha of land becomes unavailable for agricultural production because of salinization problem throughout of the world. Therefore,people are facing problem to fulfill the requirement of food. Overcome the salt stress and getting more production with saline irrigation are the hot issues now a day in research field. The content of this thesis are also deal with that problem. In this study, the response of two okra cultivars(Chinese green and Chinese red) in terms of germination and seedling growth under salt stress conditions has been examined to check salt tolerance nature of both cultivars under early seedling growth stage. Seeds of both cultivars were placed for germination in petri dish and seedling was allowed to grow for seven days in plastic cup at same proportions of NaCl and CaCl2 to make treatment like control (0), 0.6%, 1.2%, 1.8%. The results found that lower concentration of salt stress (0.6%) was not affect the germination percentage of Chinese red, but Chinese green germination rate was decreased at 0.6% level. The germination was found to be delayed at other levels and 65% reduction was found in germination of both cultivars at 1.8%salt stress. Gradual decrease in root length, shoot length, total length, fresh weight and dry weight of the seedlings were observed with the increasing concentration of salt stress. Chinese green showed more reduction in plant growth then Chinese red. According to results, Chinese green was salt sensitive whereas Chinese red, salt tolerant at early growth stage and germination period.In other experiment, two okra cultivars (Chinese green and Chinese red) were subjected to salt stress (0%, 6%,12% and 18%) with equal proportions of NaCl and CaCl2 in Hoagland's nutrient solution and followed by re-watering at levels of (6-0%, 12-6% and 18-12%). Salt stress significantly reduced photosynthetic attributes and growth parameters of both cultivars. Chinese green showed sudden reduction in photosynthetic attributes at 6% salt stress level but Chinese red showed more reduction at 12% salt stress level. Treatment subjected to 18% salt stress caused 90% redundancy in growth parameters of both cultivars compared to control. Re-watering gave a positive response for plant growth of both cultivars in different levels. Chinese green showed better recovery at 6-0% re-watering level and Chinese red showed 12-6% and 6-0%, due to its salt tolerance nature. Re-watering water use efficiency is the new technique to check water status of plant after re-watering that was used in this study and found significant result of both cultivars in different levels of re-watering. Considering re-watering water use efficiency and net photosynthetic rate, the optimum values of salt tolerance for Chinese green and Chinese red were 8.3% and 12.02%, respectively. The best re-watering degree found as salt stress level ranged from 12.02% to 6% for Chinese red and 8.3% to 2.3% for Chinese green.In other experiment, two okra cultivars,Chinese green and Chinese red were used to assess the water status and growth parameters subjected to salt stress by adding NaCl and CaCl2 with same proportion in Hoagland culture solution at levels of 0%, 0.6%, 1.2%, 1.8% and re-watering at levels of 0.6-0%, 1.2-0.6%, 1.8-1.2%. The measured water potential and physiological capacitance values were used to calculate leaf tensity. Salt stress significantly reduced water status, growth and yield. Chinese green showed more reduction as compared to Chinese red but at 1.8% salt stress reduction of both cultivars were almost same. At 1.2% salt stress level Chinese green showed more reduction then Chinese red. Chinese red growth and fruit parameter at 1.2% were almost equal fruit and growth parameter of Chinese green at 0.6% salt stress level.Re-watering had given a positive response for both cultivars to recover from higher salt stress.Dry weight, physiological capacitance, leaf tensity and salts concentration levels were used to build models. These models gave predicting re-watering levels in percentage, also gave values of dilute irrigation point for Chinese red 9.05 or 10.00 ds m-1 and Chinese green 6.67 or 5.66 ds m-1.At resulted dilution points, plants of both cultivars were under high salt stress, which emphasized the need to re-water or dilution of salts for the survival of plants. The most effective predicting re-watering level and dilute irrigation point of both cultivars were found in same regime, so these models findings were very credible and meaningful. Higher dilute irrigation value of Chinese red indicates its more tolerance ability than Chinese green. Model's equations also gave direct irrigation point of Chinese red 1.32 or 1.62 ds m-1 and Chinese green 2.07 or 0.38 ds m-1. It was concluded that re-watering water use efficiency and net photosynthetic rate the optimum values,predicting re-watering levels, dilute and direct irrigation point help to get maximum production using saline water resources. This study provided a new method for the determination of best irrigation regime or dilution point considering plant response under saline irrigation, which supports the application of agricultural engineering, to get optimum irrigation strategy in salt effected areas. To achieve economic stability of the farmers in salt effected areas, best irrigation strategy has becomes the priority of agricultural engineers and irrigation planners.