Spatial Variability Of Soil Characterization And Reversal Evolvement Of Soil Salinization In Qitai Oasis

Soil salinization is a global problem of resource and ecology, and scholars pay more attention on it. Soil salinization and secondary soil salinization are the most important factors which influence the survival and development of oasis. Soil salinization will evolve into the benign aspect naturally under certain conditions,which is called reversal evolvement of soil salinization. The course of soil salinization occurrence can be regarded as a reversible reaction, and the reaction always in a dynamic balance. Finding out the activators which can advance the reversible reaction, making the reaction become the counterreaction furthest, soil salinization will restore naturally.In order to discuss the course and feature of reversal evolvement of soil salinization, the main findings of this study are:(1) Choosing farmlands of different cultivated time in plain and oasis-desert ecotone in Qitai oasis, analyzes the changes of soil soluble total salt, pH value, organic matter. Contracting the farmland soil features of different samples and different cultivated time, with the decline of groundwater table, discusses the temporal and spatial changes of farmlands soil-salinization in different phases. The results show that Qitai oasis has already in a circumstance which is valuable for soil-salinization reversal evolvement. Groundwater table is below 5 meters, the critical point which will affect the surface salt accumulation. Groundwater mineralization degree is lower than 3g/L. With the decreasing of groundwater table and the increasing of cultivated time, the content of soil soluble total salt declined and organic matter enhanced, soil-salinization reversal evolvement has already occurred. The relation between soil salt content and groundwater table is close. When groundwater table is 3 to 5 meters, the speed of desalinization is the fastest. While groundwater table is higher than 5 meters, the speed of desalinization slows down obviously.(2) Design middle-scale sample area in middle plain in oasis, analyze and compare spatial variability of soil salt, organic matter and pH value of 10 years and 20 years cultivated farmlands. The variability intensities of soil salt and organic matter are middle, while the variability intensity of soil pH value is low. Both 20 years and 10 years farmlands soil salt, organic matter and pH value are spatially auto-correlated. Both auto-correlations and correlation ranges of the former soil characterization are higher and greater than the latter. Image maps by ordinary Kriging showed distributions of soil salt, organic matter and pH value at different time were different. Spatial changes of 20 years cultivated farmlands soil characterization are more continuous than 10 years cultivated farmlands. That is to say, along with the increasing influence of human agricultural activities (including such culture management as cultivation, irrigation and fertilization, etc.), saline soil will evolve into the benign aspect naturally.(3) Spatial variability of soil properties(soil salt, organic matter, pH value) in serious salinization area of Lower reach of plain reservoir The variability intensities of soil salt, organic matter and pH value are separately middle to high, middle and low.. The variability intensities of soil salt and organic matter are increase from surface to bottom, while the vertical deference of the variability intensities of pH value is unobvious. Auto-correlation of soil organic matter is great, though the total spatial variability is high, the variability is mainly caused by structural factors. Soil salt and pH value have middle auto-correlations, both structural factors and random factors affect spatial variability.(4) Man yinghu, serious salinization area of Lower reach of plain reservoir. With the exploration and utilization of groundwater, the groundwater level will decrease gradually. By forecast, groundwater level will below the zero flux plain, 5 meters, in 2024. Soil salt content will less than 0.3% in 2034. That is to say, the time of groundwater level under 5 meters last 10 years, and the time of farmlands cultivate last 20 to 30 years, saline soil will naturally restore into non-saline soil.(5) Salinization reversal evolvement presents temporal and spatial characters, and can be classified as three different phases: the primary, the middle and the high-level. From the aspect of time, no matter in what physiognomy positions of oasis, the longer the cultivated time last, the more the organic matter and the less the salinity become, the better the salinization reversal evolvement develop. When the time of farmlands cultivate and the time of groundwater table under 5 meters last more than 20 years, saline soil can convert into non-saline soil. In point of space, from the lower to the upside of Qitai oasis, the stage of soil salinization reversal evolvement gradually transfers to high-level.