| چکیده انگلیسی مقاله |
Introduction Reduced availability of water resources in many arid countries including Iran, particularly in response to the indiscriminate harvesting of water reservoirs and climate change, has created concerns. Therefore, the sustainable use of water resources especially in agriculture is a necessity for these countries. Strategies such as deficit irrigation and superabsorbent application are two important ways for improving water use efficiency in agricultural lands. In deficit irrigation the crop must be irrigated less than its required water. Therefore, some reduction may occur in crop yield, but the savings in water will improve the water use efficiency (Akbari Nodehi, 2011). Superabsorbent polymers also increase the nutrients and water holding capacity of soil for a long time and thereby reduce crop water requirement. However, the effectiveness of these materials could be affected by dehydration frequencies, temperature and irrigation water quality (Karimi et al., 2009). Due to the limitation of water resources in many parts of Iran, the aim of this study was to investigate the possibility of cotton production under deficit irrigation along with application of different rates of superabsorbent. In addition, simulation of superabsorbent efficiency at different levels of salinity, temperature and dehydration frequencies (swelling and de-swelling) were the other objectives in this study. Materials and methods 1. Laboratory experiments In these experiments the effects of temperature (4, 10, 20, 30 and 40 °C), salinity (0, 0.25, 0.5, 0.75 and 1% NaCl solutions at two temperatures of 10 and 25°C) and frequency of partial dehydration (from 1 to 5 stages watering and 70% dewatering) were simulated on water absorption capacity of superabsorbent polymer at laboratory of environmental stresses, Sarayan Faculty of Agriculture, Birjand University. 2- Field experiment This experiment was designed at Research Station of Sarayan Faculty of Agriculture, Birjand University, Iran, during 2014. The experiment was carried out as factorial arrangement based on randomized complete block design with three replications. Study factors were consisted of different levels of superabsorbent (0, 30, 60 and 90 kg.ha-1) and deficit irrigation [irrigation intervals of 12 (control), 15 and 18 days equal to ~120, 155 and 190 mm evaporation from pan, respectively]. Seeds of cotton (Khordad cultivar) were sown in 20 June, with 60×25 cm distances in 3×4 m plots. The harvesting of cotton was performed at three times on 27 Oct, 10 Nov and 17 Nov. At the end of experimental period the yield and quality indices of produced fibers including fiber length, uniformity index, strength, elasticity, fineness (micronaire), brightness, yellowing, ripening ratio and short fibers percentages were measured. Finally, statistical analysis was employed by using the Duncan’s multiple range test at the 5% level of probability. Results and discussion Results of laboratory experiments showed that salinity had considerable negative effects on water absorption capacity of superabsorbent in both 10 and 25°C temperatures. The amount of water absorbed by superabsorbent reduced by 73% and 85% by increasing salinity from 0 to 0.25% and to 1%, respectively. In addition, the effect of temperature changes was significant on the water absorption capacity of superabsorbent. The highest value of water absorbed by the superabsorbent was obtained at 20 °C treatment. The amounts of water absorbed at 20 °C, were 8% and 13% higher than 4 °C and 40 °C, respectively. In similar study it has been concluded that swelling of polyaspartic acid hydrogels decreased when the temperature of the aqueous media increased from 25 °C to 60°C (Zhao et al., 2005). The amounts of water absorption ability of superabsorbent during 1 to 5 watering and dewatering cycles were 266, 311, 334, 340 and 355 g g-1, respectively. Results of field experiment showed that cotton yield was significantly affected by irrigation management and superabsorbent application. Application of 60 kg ha-1 superabsorbent along with irrigation intervals of 15 days was the best combined treatment in terms of fiber production. Moreover, experimental factors had no negative effect on the quality indices of produced fibers. Conclusion Results of this experiment showed that superabsorbent application and deficit irrigation are the two potential strategies for cotton production in semi-arid regions, especially if low saline water sources are used. Acknowledgments We wish to thank Vice President for Research and Technology, University of Birjand, Iran for the financial support of the project (Approved on November 26, 2014). |