Mechanism Of Amending Salt Affected Soil Through Leaching And Phytoremediation

Secondary salinization of soil is a major limiting factor for agricultural sustainability development in irrigated agriculture in arid and semi-arid regions. At present, the problem of soil salinity is further deteriorating in inland arid regions as the dry lands have become irrigated fields, which caused the substantial rise of groundwater table. The majority of comparative studies suggested that phytoremediation (plant-assisted approach) is more effective in the amelioration process in recent years. Rhizosphere is an important interface in substance exchange and energy transformation between plants and soil. Affected by physiological activities of plant roots, there is a marked difference in physichemistry properties between the rhizosphere soil and bulk soil. Based on a calcareous salt-affected soil in the irrigated region of Qingwangchuan, Gansu, a rhizobag experiment was conducted on six salt-tolerant plants to investigate dynamic changes of pH, EC (Electrical Conductivity) and salt ions in the rhizosphere, bulk soil and plant, and to compare the differences between them at the different plant growth stages. The results showed that:1, Soil pH in six tested plant groups decreased with the extension of incubation days. There was significantly (P<0.05) lower pH in rhizosphere soil in Xinjiangdaye (Medicago Saliva. L.cv.Xinjiangdaye) and Zhonglan No.1 (Medicago Sativa var Zhonglan No.l) than in than the other four tested plants, such as sunflower (Helianthus annuus), common beancaper (Zygophyllum xanthoxylum), Alkaligrass (Puccinellia chinampoensis) and barley (Hordeum vulgare var nudum). The value of soil pH in the rhizosphere and bulk soil exhibited a trend of dynamic changes in different incubation days.2, Soil EC in six tested plants decreased with the extension of incubation days. EC in the rhizosphere and bulk soil exhibited a trend of dynamic changes in different incubation days and different plants. EC was significantly higher in rhizosphere soil than in bulk soil for common beancaper and xinjiangdaye, but EC was no different between rhizosphere soil and bulk soil for sunflower, barley and control group. EC was significantly higher in rhizosphere soil than in bulk soil for zhonglan No.1 and Alkaligrass after a 90-day growth period. 3, Concentrations of six major salt ions in six tested plants significantly decreased with the extension of incubation days. K+ concentrations reduced significantly in the rhizosphere of six tested plants, The distribution of the other major five salt ions such as Na+, Ca2+, Mg2+, Cl- and SO42- in the rhizosphere and bulk soil exhibited a trend of dynamic changes in different incubation days. Ca2+, Na+, Mg2+and Cl- concentrations increased mostly in the rhizosphere of common beancaper at the different growth stages. However, SO42- concentrations increased mostly in the rhizosphere of barley.4, Concentrations salt ions such as K+, Na+, Ca2+ and Mg2+ in shoot and root of different plants exhibited a trend of dynamic changes in different incubation days. K+ concentrations higher in sunflower than the other five tested plants, such as xinjiangdaye, zhonglan No.l, common beancaper, alkaligrass and barley at the different growth stages. However, Na+, Ca2+ and Mg2+ concentrations increased mostly in common beancaper than the other five tested plants, such as xinjiangdaye, zhonglan No.1, sunflower, alkaligrass and barley at the different growth stages. The distribution of salt ions in shoot and root of different plants exhibited a trend of dynamic changes in different incubation days.5,The measure (complex measure)that combined leaching with phytoremediation was more efficient than using leaching singly for removing Na+,Ca2+ and Mg2+,but except for K+. As for the amending effect of complex measure, The average removing quality of Na+, Ca2* and Mg2+that salt-tolerant plants absorbed in different incubation days was the smallest, amounting 0.46% (S.D= 0.42%),0.63%(S.D=0.61%) and 0.62%(S.D=0.40%) of the total quality respectively, The average removing quality of Na+, Ca2+ and Mg2+ that leaching measure singly in different incubation days was the largest, amounting 60.09%(S.D= 7.23%),51.60%(S.D=9.23%) and 77.00%(S.D=11.06%) of the total quality respectively, and the average removing quality of Na+, Ca2+ and Mg2+ that leavened by root of different plants in different incubation days was in the middle, amounting 39.45%(S.D=7.41%),47.78%(S.D=9.68%) and 22.40%(S.D=11.24%)of the total quality respectively.So The average quality of Na+, Ca2+ and Mg2+ that six salt-tolerant plants absorbed in different incubation days was inappreciable during growth periods.6, We should consider three key coupling factors:the distance between sampling site and plant rhizosphere, different plant species and different plant growth stages.when pH and salt contents in the saline soil were measured.