Distribution Characteristics Of Seleniium In Soils And Winter Wheat Grain Of Main Wheat Production Areas Of Shaanxi(China)

Selenium is an essential trace element for humans and animals,and its lack or excess is closely related to human health.Identifying selenium content and its spatial distribution characteristics in soil and main grain in one area is an important basis for exploring the local selenium nutrition status of local residents.Wheat is the third largest food crop in China,and it is also a daily staple food for northerners.This paper takes 32 counties in the main wheat producing areas in Shaanxi Province as the research object,collected and measured 522surface soil samples and the corresponding wheat grain samples for selenium content,and analyzed the spatial distribution characteristics of selenium content were analyzed in the area and the distribution of available selenium content in a wide range of soils were systematically evaluated.In addition,the effects of precipitation and topography on soil selenium bioavailability and further on human selenium daily intake were explored.Jinghuiqu Irrigation area was taken as an example to investigate the possible effects of artificial irrigation on the accumulation of selenium in soil and wheat grain.The main results obtained are as follows:1.The content of Se in the soil of main wheat area in Shaanxi ranged from 0.020 to1.044 mg·kg^-1,with an average content of 0.171±0.088 mg·kg^-1.Soil samples belong to Se deficient and potential deficient category accounted for 62.3%of the total soil samples in the study area,while Se moderate soil accounted for 35.2%of the total,and Se-rich soil accounted for only 2.5%.It shows that Shaanxi's main wheat production areas are Se-deficient areas in general.The lowest Se content in soil was found in Fengxiang county(0.103±0.029 mg·kg^-1)among 32 counties,while the highest Se content in soil was observed in Hancheng city(0.398±0.222 mg·kg^-1),the later one was 3.8 times of that in Fengxiang.The distribution of soil Se content in the entire study area was moderately variable,and the spatial distribution of soil Se content was heterogeneous.The Se content in the soils of Hancheng city,Yanliang district,Hua county,and Hu county was higher,while that in the northern areas of Baoji city,Xi'an city,and Xianyang city is lower than in other areas.2.Se content in wheat ranged from 0.0001 to 0.795 mg·kg^-1,with the mean value of0.056±0.064 mg·kg^-1,reached moderate Se level.The moderate and high Se content in wheat samples accounted for 52.3%of the total samples,which were 30.5%and 21.8%,respectively;while the Se deficiency level occupied 23%of the total,and the critical Se deficiency was 24.7%.From the point of view of spatial distribution,the study area have reached spatial variability,and the high Se concentrations in wheat have been distributed in discrete spots.Such as,the junction of Wugong and Xingping,the junction of Fuping County and Pucheng County,the northern part of Hancheng City,the junction of Yanliang and Lintong,and parts of Jingyang County.The average daily intake of Se by wheat is 16.9?g·d^-1,and the Se intake through cereals accounts for 33.7%,which was much higher than in other areas,indicating that the level of Se intake by local residents through wheat is relatively high.3.The available selenium content in soil was 0.017±0.009 mg·kg^-1,accounting for 11.5%of the total Se content in soil,which was higher than that in Ping'an of Qinghai.Among 32counties,the highest one was found in Changwu?21.5%?,and the lowest one was observed in Hancheng city with the highest content of selenium in soil?4.5%?.The soil available Se content was significantly correlated with soil total Se content?p<0.01?.In terms of spatial distribution,the available Se content of soil had the same trend as the total Se content of soil with a clear distribution pattern.That is,the low content was located in the northern part of the Middle East,while the high content was concentrated in the southwest,namely the Hu County and Xingping County.In addition,precipitation has no significant effect on the bioavailability of selenium.At the same time,there was an extremely significant negative correlation between altitude and available Se content in soil,total Se content in soil,and wheat Se content.It showed that the total Se content in soil,available Se content in soil and selenium content in wheat all showed a downward trend with the increase of altitude.4.The soil selenium content in the Jinghuiqu Irrigation area was the highest in Yanliang District and the north of Lingtong.There was no significant difference among the other regions.The Se deficient and potential deficient soil samples accounted for 76.92%of the total samples,while the appropriate amount of selenium in the soil accounted for 20.19%,indicating that the soil in the area belongs to the level of Se deficiency.The Se content of wheat in the irrigation area was higher than that in the entire Guanzhong area,mainly due to human management,and the Se content accumulation caused by irrigation.Generally speaking,total soil Se content does not fully reflect the level of Se in an area,which is related to soil Se availability,plant Se absorption capacity,climate and topography.Therefore,Se supply capacity of soil and plant uptake ability must be comprehensively considered in Se biofortification practice.