|Other Abstract||Manasi irrigation area is typical oasis agriculture of Xinjiang. The serious soil salinization phenomenon, which is caused by the drought climate conditions, is having a serious influence on the stability of the agricultural development of social economy and ecological environment. This paper chooses the Manasi irrigation area as the research area, analyses the characteristic of regional soil salt with the method of correlation analysis and statistical analysis, analyses the spatial-temporal change of soil salinization with "3S"(include GPS, GIS and RS) technology and the dynamic model of quantitative and the transfer matrix. Besides, it analyzes the driving factors of soil salinization in the irrigation area, on the basis of the partition in the studied area, and raises some countermeasures which can improve that kind of situation according to the characteristics of the different regions. Research results provide scientific basis and technical reference to the sustainable development and improvement of land utilization of Manasi irrigation area.
The main conclusions of this paper include the following:
1. The mainly cation was Na+ and Ca2+, while Cl- and SO42- was main anion in 0~30 cm soil layer in the study area. The spatial variability of different salinity indexes changed greatly. Total salts, Na+, Cl- and SO42- was a strong variability, HCO3-, Ca2+, Mg2+ and K+ in the medium variant, while pH belonged to the weak variation. The correlation analysis showed that SO42- and Na+, Ca2+, Mg+, K+ positive correlation were significant (P<0.01), which had the highest correlation with Ca2+ and the correlation coefficient reached 0.914, and Cl- was significantly positively correlated with K+ and Na+ (P<0.01) and the correlation coefficient of Na+ was 0.912. However, HCO3- and other ions had no significant correlation.
2. The main types of soil salinization were sulfate and chloride- sulfate in Manasi irrigation area, which the alluvial fan area dominated by sulfate, dry delta and alluvial plain with chloride-sulfate. The Kriging interpolation results showed that the salt content in the alluvial fan area was the lowest, which basically belonged to non-salinization soil; the upper part and the southeast part of the alluvial plain as well as the dry delta area were mainly dominated by mild salinization. Semivariance analysis also found that total salt, Na+, K+, Ca2+ and SO42- could be best described by exponential model; Mg2+ and HCO3- conformed to the spherical model; and Cl- accord with Gauss model. In addition to Na+, Ca2+ and Cl-, salt and other ions showed a strong spatial correlation, and the ranges of salt ions varied from 3 m to 374 m, which was the result of structural factors.
3. In nearly 30 years, Manasi irrigation area of non-salinization of arable land and slight salinization of arable land changed dramatically, the area was constantly increasing trend. Moderate salinization of cultivated land total area reduced, mainly to slightly salinized cultivated and non-salinization of cultivated land conversion. Saline soil area continues to decline, mainly transformed slightly salinized cultivated land and moderate salinization of cultivated land. The transfer matrix analysis also showed that the transfer between cultivated land (include non-saline cultivated land and saline cultivated land) and solonchaks were larger and become the main conversion.
4. The phenomenon of soil salinity in Manasi irrigation area was widespread and showed a strong spatial variability, which was mainly distributed in the upper part of alluvial plain, the gently low-lying topography, the high groundwater levels in fan-shaped overflow belt and the surrounding areas distributing in plain reservoir. Grate changes had taken place in the soil salinity of the internal and external researched region from 1985 year to 1998 year. The internal researched region such as the southwest and southeast underwent the biggest changes, but the external change was smaller. The overall change was small from 2006 year to 2014 year.
5. The natural and artificial factors had an influence on the development processes of soil salinity. The natural factors such as climate condition, organic salt and so on were the internal cause, which promoted the occurrence of soil salinity. However, the extensive development and utilization of the land, the leaky reservoir systems, the effect of drip irrigation and the imperfect system of irrigation and drainage project were external.
6. On the basic of the spatial characteristics soil salinization, salt accumulation characteristics, landform, groundwater depth, groundwater salinity, the Manasi irrigation was divided into five improvement areas. Improved governance zones for different soil salinization, proposed the improvement of the corresponding propositions and countermeasures.|