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Effects of Agronomic Practices on Soil Water-Salt Dynamics in Cotton Fields under Sea Ice Water Irrigation Conditions

CAI Dianxiong1,2,3,HU Yujiao2,ZHAO Quansheng2,ZHENG Yan2,WU Xueping2, WU Huijun2,ZUO YUbao2,WANG Xiaobin2,HUA Luo1 (1.Capital Normal University,Beijing 100048,China; 2. Institute of Agriculture Resources and Regional Planning Chinese Academy of Agricultural Sciences, Key Laboratory of Plant Nutrition & Nutrient Cycling Ministry of Agriculture,Beijing 100081,China; 3. Key Laboratory of Dryland Farming,MOA,China,Beijing,100081,China)  
Agricultural productions are primarily constrained by increasingly freshwater resource shortage and land salinity threats. Freshwater shortage is one of the most important constraints on agricultural productions over the coastal areas of the Bohai Bay. Exploitation of usable water resources (e.g., sea ice water) and effective water-saving irrigation methods for improving crop production on salinity-affected lands has been receiving more and more attentions in China. In the present work, a field experiment using sea ice water of salinity of 3‰ for cotton irrigation in combination with four treatments of fertilization practices (i.e., inorganic fertilizer, organic manure + inorganic fertilizers, soil conditioner + inorganic fertilizers, and CK treatment), was conducted to quantify the effects of irrigation sources from well water and sea ice water and fertilization on the changes in soil water contents and salt contents during growth periods of cotton over the coastal saline soil. The results indicated that during the period of 2007-2008 soil moisture contents under the sea ice water irrigation condition at seedling and flowering stages were significantly higher than that under the well water irrigation, particularly for the soil moisture content in the 0-40 cm layers at pre-sowing irrigation. It was found that soil moisture contents under well water irrigation with the PAM-treated irrigation increased significantly compared with the PAM-untreated irrigation. The results also showed that downward movement of soil salt under the sea ice water irrigation condition was faster than that from the well water irrigation. It was estimated that the 1-m profile soil desalinization rate under sea ice water irrigation was about 40% of the initial soil salt contents at the cotton harvest after rainfall season. In 2007, the 1-m profile soil salt amounts at the cotton harvest were leached by about 11210 kg/hm2 with the PAM-treated irrigation, but by about -22610 kg/hm2 with the PAM-untreated irrigation. It was pointed out that soil salts could be effectively leached by irrigation and rainfall in agronomic practices irrespective of whether sea ice water or well water irrigation was utilized. In 2007, soil desalinization rates in the 0-40 cm layers were 53-55% higher for a combined application of inorganic fertilizer and soil conditioner (gypsum), or a combined application of inorganic fertilizer and organic manure than that of the application of the inorganic fertilizer alone. There was no significant accumulation of salt in soil profiles in case of sea ice water irrigation at the cotton harvest compared with well water irrigation. It can be concluded that the use of sea ice water of salinity of 3‰ for cotton irrigation combined with agronomic practices, such as inorganic fertilizer combined with soil conditioner, or inorganic fertilizer combined with organic manure, could accelerate water infiltration and improve soil desalinization to certain degrees.
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