The Characteristics And Causes Of The Arid Region Of Northwest Jinta Oasis Soil Salt-ion Distribution Analysis

In arid areas, the oasis is the primary place of human production and living, which not only is the backing of agriculture, animal husbandry production, the construction of villages and towns, but also is the largest region that impacts human. The development and utilization of oasis play an important position during the western development, in which the soil resources of oasis are the base of the sustainable development of agriculture. However, with the development and growth of oasis, there have been serious problems for the ecological environment, such as soil degradation, land desertification, soil salinization and the resulting degradation of vegetation and species extinction or other practical problems. These not only had greatly affected the human production and living, but also seriously endangered the stability of oasis. Therefore, the study on land use change and soil system stability of oasis is of great significance to the agriculture sustainable development in arid areas.Jinta Oasis is a very typical artificial oasis in arid area of China, which is regarded as one of the demonstration areas that related to the development and rehabilitation of land resources in the northwest of China. It is a very typical and artificial oasis in the arid areas of China, regarded as one of the demonstration areas that related to the development and rehabilitation of land resources in the northwest of China. This paper concerns the ecotone geographical features of oasis and desert, which based on the reach of the worsening ecological environmental problems in Jinta Oasis agricultural areas, combining with previous studies and research findings.With the soil sampling data of Jinta County oasis 2006, 10 elements reflecting soil salinity characteristics were selected, namely, pH, conductivity, total salt, each component of salt ions such as Ca²⁺,Na⁺,Mg²⁺,K+,SO₄^2-,Cl^-,HCO₃^-.Using the principles of mathematical statistical and geostatistics combined with GIS technology, mainly analyzing the spatial distribution characteristics of salt ions and the causes related. The analyzing results show that: (1) Statistical analysis shows that the majority cation of the salt ions in the soil surface is Na + ,while the main anions are Cl^- and SO₄^2- in the study area; The three types of ions occupied 80.36% of the total salt content, which were predominant. Salts in the soil area was mainly NaCl and Na₂SO₄, so it was primarily chloride- sulfate salts soil in the aera. Point of view from the coefficient of variation, apart from the variation coefficient of HCO₃^- being 25% and medium variant, the other coefficient of variation of the salt ions was above 100%. This indicated that the salinity of the soil had a strong spatial variability, reflecting the complexity of factors in the research zone. The total salt content of non-agricultural land soil was much higher than that of agricultural land soil.Though it was mainly non-saline soil in Oasis, saline soil and salinized soil still showed a considerable proportion. PH value of soil samples in the reach region ranged from 7.31 to 8.50, being 7.86 on an average, suggesting that it was mainly alkaline saline soil. pH value was small in the spatial variation but distributed uniformly,. The average pH value of non-agricultural land was smaller than that of agricultural land, showing that human factors were more notable in affecting agricultural land. (2) Semi-variogram analysis shows that the change process of semi-variance analysis of salt various elements ranges from11000 m to 81400 m.The total salt component and related ions both showed moderate spatial correlation.The nuggets of PH value was relatively lower than the sills by 25%, indicating that the structural factors affecting the distribution were severe and so lead to the spatial autocorrelation of the sample points increase. (3)The Kriging interpolation chart of the surface soil salinity and the total content of ionic composition reflect that the spatial distribution of most salt ions in the study area is of high similarity and presented an increasing trend from the central and southern direction toward the northwest and northeast. The lowest value concentrated near Jinta tow which lied in the south-central urn of the oasis, while the highest value in the northwest of Xihong Team and north-east of the village of Zhuangzi nearby. In the tow of Xiba and Da zhuangzi, the total salt content was high and a degree of salinization existed in some places. Along the east and west of the irrigation area, the content of salinity increased from upstream to downstream gradually. The low terrain where water can not overflow existed the relatively high content of soil salinity, such as the edges of small lakes, barren land and woodland etc. The spatial distribution of pH value was that the value decreased from southeast to northwest also toward northeast. The trend of spacial change between PH value and total salinity presented negative correlation. (4) Vertical distribution of soil salinity: the total salt content of soil of three samples generally decreases with the increasing of depth, which ranged from 0.5 to 4.5 g/kg, reflecting that the salt content of surface soil was higher than that of the lower soil. So there was the characteristic of salt aggregating toward soil surface. In the different depth profiles, soil pH values of three samples are all greater than 7, generally among 7-8.2, declining as the soil depth increased. (5) The formation of spatial distribution of oasis soil salinity was mainly caused by two aspects including natural factors and human factors. Natural factors contained arid climate, closed basin topography, a variety of soil types, soil texture, the regulation of groundwater and the salt accumulation of vegetation, while human factors including different land use types, diversity of crop planting structure, unreasonable use of water resources , irrigation and artificial fertilization, etc.In this paper, limited sampling datas and methods which combined conventional statistics and geostatistical were adopted to analyze the spatial distribution of soil salinity and its causes. Further analysis was given basing on the results, proposing some references about strengthening the protection and sustainable use of oasis soil resources. The last purpose was to provide some references for the soil system stability and sustainable development of agriculture in oasis.