| The characteristics of temporal and dimensional evolution and spatial variation of soil trace elements in farmland at prefecture-level city,agricultural district and county scale are unknown.This paper took soil samples of rice-wheat rotation in Xinghua,Taixing,Jingjiang,Jiangyan,Hailing and Gaogang GPS positional sampling was carried out on the topsoil(0-20cm)in the study area from 2017 to 2019.The contents of total manganese,total molybdenum,total selenium and total boron in soil were determined.Based on classical statistics,geostatistics and GIS spatial interpolation,we studied the spatial and temporal variation characteristics of soil trace elements and evaluated the grades of soil trace elements at different scales.The main results are as follows:1.The contents of total manganese,total molybdenum,total selenium and total boron in Taizhou from 2017 to 2019 showed medium variability on the whole.While the total molybdenum in 2019 showed strong variability.The total selenium in Gao gang in 2017 and the total molybdenum in Xinghua and Jiangyan in 2019 showed strong variability.The rest showed medium variability.From 2017 to 2019,the total manganese of soil in Taizhou increased year by year,while the total molybdenum,selenium and boron rose first and then fell.From the county scale,the average content of total manganese in Taixing rose first and then fell,while that in other regions of Taizhou increased year by year.The average content of total molybdenum and total selenium increased first and then decreased in three years.Except that the average content of total boron in Xinghua rose first and then fell and that in Gaogang fell first and then rose,the total boron in other counties of Taizhou decreased year by year.2.In terms of spatial variation,the ratio of nugget value to pedestal value of the four trace elements was in the following order:total manganese>total selenium>total boron>total molybdenum in 2017,total manganese>total boron>total selenium>total molybdenum in 2018,and total manganese>total boron>total molybdenum>total selenium in 2019.The content of total manganese is the largest and the other elements fluctuated from year to year.The ratio of total molybdenum,total selenium,total boron in 2017,total molybdenum,total selenium in 2018 and 2019 to the base value was less than 25%,indicating that it was affected by regional factors and less affected by random factors.The ratio of total manganese in 2017,total boron in 2018 and total manganese and boron in 2019 was between 25%and 75%,indicating that it was not only affected by regional factors,but also affected by random factors such as human activities.The total manganese in the soil from 2017 to 2019 was high in the north and south and low in the middle;the total molybdenum was high in the middle and south;the content of total selenium was high in the south;and the total boron was high in the south and northwest corner.3.From 2017 to 2019,the total manganese and total boron content of soil in Taizhou were positively correlated,while the total molybdenum and total selenium content were negatively correlated.From 2017 to 2019,the correlation between total manganese and total selenium content showed a trend of gradually increasing and showed a negative correlation.In 2017 and 2018,the correlation between soil total molybdenum and total boron content was consistent,both of which were significantly positive.The correlation between total selenium content and total boron content in 2018 and 2019 was extremely significant and negative.According to the grade evaluation of total manganese,total molybdenum,total selenium and total boron trace elements in Taizhou,it was level 5,level 5,high grade,level 5 in 2017,level 5,level 1,high grade,level 4 in 2018,level 4,level 5,appropriate amount level 5 in 2019.4.The spatial distribution of soil trace elements in different agricultural areas bounded by the Old Tongyang Canal was different in Taizhou.Except for the total selenium to Gaoshatu agricultural area in 2017 and the total molybdenum to Lixiahe agricultural area in 2019,all of them showed medium variation intensity.From 2017 to 2019,the variability of total manganese and molybdenum was Lixiahe agricultural area<Gaoshatu agricultural area.There were differences in the variability of total selenium and total boron between years on both agricultural areas.There was no significant difference in the contents of total manganese and total boron between two areas from 2017 to 2019.But there were differences in total molybdenum and total selenium.During the three years,the contents of total molybdenum and total boron showed extremely significant correlation in two agricultural areas.The correlation of total selenium in Lixiahe agricultural area and Gaoshatu agricultural area in 2018 was also extremely significant.There was no significant correlation between total manganese.The content of total manganese and total molybdenum in Lixiahe agricultural area was higher than that in Gaoshatu agricultural area.The content of total selenium in Gaoshatu agricultural area was higher than that in Lixiahe agricultural area and the distribution of total boron content was not obvious at both areas.In 2017 and 2018,the content level of total manganese in the two agricultural areas was 5 and it was 4 in 2019.In 2017,the total molybdenum content in Lixiahe agricultural area was rated as level 5 and the Gaoshatu agricultural area was rated as 4.In 2018,the two agricultural areas were rated as level 1.The average annual molybdenum content in 2019 was rated as 5.In 2017 and 2018,the total selenium level in the two agricultural areas was high and it was moderate in 2019.Except in 2018,the total boron grade in Lixiahe agricultural area was level 4,the others were 5.5.We took Gao gang as a research area.The distribution characteristic of microelements in soil and different organs of wheat was soil>leaf>grain>stem of total manganese,leaf>grain>stem>soil of total molybdenum,soil>stem=leaf>grain of total selenium.The distribution characteristic of total boron was similar to that of total manganese.The coeficient of variation of total molybdenum in soil was higher than that in wheat organ and tissue,but the characteristic of total manganese,total selenium and total boron was not obvious.The variability of total molybdenum,total selenium and total boron in soil was greater than that in stem and the spatial variability of leaves was also greater than that of stem Except for total manganese,the spatial variability of total molybdenum,total selenium and total boron in stem was the highest,while that of total molybdenum,total selenium and total boron was small There was a significant positive correlation between the contents of total manganese and total boron in soil and wheat stem.While there was no correlation between total molybdenum and total selenium in soil and in the stem,leaf and grain of wheat.In 2019,the average value of total manganese and total molybdenum in Gaogang reached the appropriate level,which can meet the needs of crop growth.The total boron was deficient and the total selenium content was moderate. |
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