Spatial Variability Of Salts And Nutrient In Saline Soil And Chemical Characteristic Of Elements In Halophytes Of Xinjiang

Ecological environment are frail in arid area in Xinjiang, and its accounts for 1/3 of the national total area. Salinization is a common phenomenon in Xinjiang, which always with seriously nutrient draining. Valley of Weigan River locates on the northern edges of Tarim basin was taken as the study area, which is the typical soil salinity area. Spatial variability of salt ions and nutrient has been studied by using chemical and geostatistical method. And the chemical characteristics of main halophyte's element in the soil-plant system have been studied, too.GPS was used to collect seventy soil samples for spatial analyses in the study area where about 200km².Contents of the total salts, Ca²⁺, Mg²⁺, K⁺, Na⁺, SO₄^2-, Cl^-, HCO₃^-, soil nutrient (total N, P, K and available N, P, K and organic matter) and pH in top soils (0³0cm) were determined. Then geostatistics combined with GIS was used to research spatial variability of them. The Kriging method was applied to estimate the unobserved points and then the precise contour maps were obtained. By this way, the spatial variability of soil salt ions, pH and nutrient could be reflected directly.The spatial variability results of total salts and salt ions indicated that the coefficient variation of pH was weak variation, Ca²⁺and HCO3- were moderate variation, the total salts and other ions' coefficient variations were strongly variation. All those responded that the salt ions in the research area were affected by complex factors. The chemical analysis of semivariograms indicated that total salts were best described by spherical model; Mg²⁺, K⁺, Na⁺, SO₄^2-, and Cl^- fitted exponential model; Ca²⁺ fitted Gauss model; and HCO3- showed the pure nugget effect. The ranges of soil salinities varied from 143m to 641m. The results also indicated that except for HCO3-, the spatial correlations of other tested parameters were moderate spatial dependence, but the degrees of spatial heterogeneity were different. Expect K+ and HCO3-, other ions spatial structures and content distributions have the obvious directivity and the continuity.The spatial variability results of nutrient showed that the variations of nutrient elements all were moderate and the coefficient variations were between 17.0% 93.9%. The relevant analysis showed that the soil salts with available nitrogen and phosphorous were significant negative correlation, but with available potassium was a significant positive correlation. Each nutrient element could be fitted by different model. Total nitrogen and phosphorous and available potassium were best described by exponential model, available nitrogen, phosphorous and total nitrogen fitted spherical model, and organic matter fitted Gauss model. The results also indicated that except total nitrogen and available were weaker spatial dependence, the others were moderately spatial dependence. And their ranges varied from 143m to 641m, which reflected different spatial correlations of various variables, and the result was affected by the structure factor and the stochastic factor together. The Kriging map indicated that the contents of the nitrogen, the phosphorus and the organic matter were low level, and the total nitrogen was in the extremely low level in the research area. The contents of phosphorus element and the organic matter respectively accounts for 80% and 50%, which were low and intermediate level. Only the potassium content was the high-level in entire area.Chemical element composition of plant can reflect the salts and the nutrient that the plant absorb or accumulate from the soil under the certain habitat condition meanwhile can reflect their salty tolerant degree. Several kinds of main halophytes (Alhagi sparsifol, Tamarix ramo sisima, Phragmites communis, Halostachys caspica, Halocnemum strobilaceum, Nitraria) and their group falls' were taken to study the relations between content of chemical element difference and salt-tolerant of the halophytes. The characteristic content of important salt ions: K⁺, Na⁺, Ca²⁺, Mg²⁺ and Cl^- in soil-plant system were studied. The positive ions have obvious accumulation phenomenon in plant's leaf and stem. Cl^- didn't have the accumulation phenomenon in plant, but the Cl^- content was very high in the root soil of the Phragmites communis and Halostachys caspica. Content of S in above-ground and below-ground of halophytes was reducing along with the SO₄^2- content increasing in the soil, which may show that high salt ions can suppress the halophytes to absorb S element. Contents of nitrogen element in the halophyte were no accumulation phenomenon. And contents of phosphorous in the soil were higher than it in the halophyte, which indicated that it is hard to absorb phosphorous from the saline soil. Organic acid was the highest content in tested organic solute, which showed that it is one of the most important osmosis-reagent in the studied halophytes. The soluble sugars content of halophytes, expect Tamarix ramo sisima, were the aerial parts higher than the underground part. Proline amino acids was not the major amino acid in the Phragmites communis, but a majory of amino acid synthesized by the other halophytes are praline acid. The reaserach indicated that different halophytes have different salt-tolerant mechanism. Alhagi sparsifol, Halostachys caspica, Halocnemum strobilaceum and Nitraria are the dilution salts halophytes and the Tamarix ramo sisima is the absorption salts halophyte, and the Phragmites communis mainly evaded the salts to adapt the saline environment.Combined with chemical and geostical method, accurate spatial variabilits were obtained by using the limited dates, and the characters of distribution and migration of soil harmful salt-ions and nutrient in two-dimensional were deterimend. And different elements content of salt-ions and nutrient, which have the relations with halophyte and salt-tolerant mechanism, have been studied in this article. These entire have the reality instruction and significance to formulate the reasonable improving saline soil and cultivating the fetilizer.