The Distrbution, Migration And Enricichment Law And Influencing Factors Of Se In Purple Soil Of Chongqing

Selenium is an essential element for human and animal,and it is also important components of nutrition for plants.The content of selenium directly impacts on the health of variety biology in environment,excessiveness or lack of selenium will cause disease;The right amount of selenium not only to advance metabolism of crops,to improve crops yield and quality,but also to play disease prevention,immunization and anti-cancer effect for animals and human.Soil as the hub of ecological environment,the content and conformation of selenium directly impact on absorption of selenium for plants,or whether it is excessive,and it will affect the growth,development and reproduction of animal,and ultimately affecting human health through the food chain;In the entire system of soil - plant - animal -human,the selenium from the soil and water,and water-soluble selenium in soil is the key to the nutritional level of selenium in the decision system.Purple rock and soil is the main soil-forming rocks and soil types in Chongqing,and it is most important soil types for agricultural land.According to the literature shows,the area of purple soil in Chongqing is the lower seleniumthe distribution of our country,and there is concentrated area of selenium reaction disease(such as Keshan disease).But now,the related study about the cause of low selenium and the effect of rock of different time on selenium and the water-soluble selenium in purple soil in Chongqing are less,in particular,purple soil profile for the study to explore the profile of selenium enrichment and migration has not been reported.In the past,different analytical methods to analysis selenium in purple soil in Chongqing cause very inconsistently conclusion.So,in this paper,studied on purple soil profile in Chongqing,established the method of water-soluble selenium in soil,through studied on the rock different of geological time and the development of purple soil, discussed the content and distribution of purple rock of different geological periods and the content, distribution,enrichment and transference,and influencing factors of total Se and water-soluble Se in purple soil,found some salient features and the law of selenium in the purple rock and soil.The results are as follows:(1) The content of Se in purple rock rang from 0.012 to 0.090 mg/kg,averaged 0.041mg/kg,the content of Se in purple rock of different geological period are apparent differences,coefficient of variation is 62%,and the sequence of Se contents is J₂sn＞J_1-2z＞J₃p＞J₂s;The purple rock of same geological period,the content of Se in mudstone is higher than sandstone,which is basically the same as the past.(2) The content of total Se in test soil sample rang from 0.077 to 0.566mg/kg,averaged 0.194mg/kg,and the content of Se in dry land soils is 0.174mg/kg,paddy soil is 0.226mg/kg, overall a low-selenium soil type partial middle,which is not consistent with previous studies. The content of total Se in purple soil of different geological rock development is increasing tend by the new to old of geological periods,and the sequence of Se contents is J₃P＜J₃sn＜J₂s＜J_1-2z.The distribution of total Se in purple soil of Chongqing is Western Region＞Central region＞Northeast region,collectivity as the distribution of piece shape,and thr higher selenium soil mainly concentrate in the aqueous landscape.(3) This paper used boiling bath to concentrate water extracts from soil under the presence of nitric acid and added Fe3³⁺ as fixative,then digested the extracts with mixed acid,and determined the selenium content by hydride atomic fluorescence spectrometer.The results shows that the determination values raise 40%or more than that of untreated soil,the recoveries are between 98～102%,the variation coefficient≤0.3%.(4) The content of water-soluble Se in test soil sample rang from 0.40 to 5.89μg/L,averaged 0.194μg/L,percentage of the total amount of selenium is 0.1%～3.7%,averaged1.7%;The Correlation between the content of water-soluble Se and geological periods is not distinct.(5) The total selenium and water-soluble Se in purple soil profiles gradually reduce with the deepening of the soil depth,and it is the enriched characteristic,and significantly aggregation in topsoil;The sequence of Se is Topsoil＞Heart soil＞Bottom soil.The selenium in purple soil of Chongqing mainly from the addition of exogenous,and it is a stage of cumulative and adsorption for a long-term trends;But,the addition of exogenous will shuod be studied.(6) It is the reverse law of total Se and water-soluble Se with the degree of soil development,from shallow to deep of soil development,the content of total Se gradually increasing,but to reduce for the level of water-soluble selenium.On the base of the same degree of soil development,the content of total Se gradually increases with the geological period's growth,that is J₃p＜J₂sn＜J₂s＜J_1-2z,and there do not find a similar law between the content of water-soluble Se and the geological age.(7) The analytical results showed that:the biogeochemical factosr in favor of enrichment of selenium,but also restrictive factors of selenium desorption.The influencing factors of selenium levels,distribution and migration enrichment are Rock,soil pH,organic matter,soil total nitrogen,total phosphorus,total potassium,metal oxides,soil texture and land use patterns,in which rock is the most important reason,followed by soil physical and chemical nature and the farming system.