Effect Of Soil Acidification And Phosphorus Levels On The Bioavailability Of Selenium In Soil

The relationship between microelements and human health has been a focus of scientific research,and an issue that people are more concerned with.As an essential trace element,selenium is of a very close relationship with human health.In a large number of areas in China,local residents had suffered from keshan disease and kashin-beck caused by selenium deficiency.In addition,many studies have confirmed that selenium has certain effect on preventing cancer.In recent years,people have paid more and more attention to health,and the benefits of selenium on human health have been realized.Therefore,the exploitation of selenium-rich products has become a very promising research subject.Our team carried out the project of pollution-free tea investigation of Jiangsu Province in 2002.We found that the content of selenium in tea garden soil of Yi-Li area was high which reached the selenium-enriched level.It's an opportunity for Jiangsu Province to develop the selenium-enriched tea industry.However,by sampling and analyzing top soil in each typical tea garden,we found that there was a severe acidification issue of tea garden soil in Jiangsu Province,which has an adverse effect on the yield and quality of tea.This study was based on the previous studies of our team.Some typical tea garden soil was sampled from six major cities in Jiangsu Province,including Nanjing,Zhenjiang,Yangzhou,Changzhou,Suzhou and Wuxi.Then,the relationships among pH,available selenium and phosphorus were analyzed.Since the phosphorus and selenium in soil,which are of the similar chemical behaviors,are in the form of anions,there is interaction between phosphorus and selenium.Therefore,phosphorus can be used to regulate the content of selenium in soil.By combining the latest data with past data and analyzing the relationship among pH,selenium and phosphorus,this research provides theoretical basis for the production of selenium-enriched tea.By analyzing the average pH values of typical tea garden soil from the past 13 years,the acidification of typical tea garden soil in Jiangsu Province declined and subsequently rose.From 2002 to 2011,the average pH values showed a declining trend.After 2011,the overall trend obviously rebounded,reaching the maximum of 4.74 in 2015.Based on this phenomenon,the proportions of different pH values of tea garden soil were analyzed from 2003 to 2015.In 2015,66.7%tea garden soil is of the pH range(4.5-5.5)that suits for the growth.Meanwhile,the number of tea garden in the range pH<4 has declined to 0.However,soil acidification still existed in some tea gardens.In summary,although the phenomenon of soil acidification in Jiangsu Province persists,the overall situation has improved.By analyzing the previous data,compared with the lower pH levels,the selenium activation rate is higher at the higher pH levels.The content of available selenium increases as the rising of pH value.The effect of pH on soil available selenium is discussed within a wide range.Therefore,in a narrow range,the effect of pH on the effectiveness of selenium in the soil cannot be reflected properly.With the increasing of pH range,the correlation between pH values and selenium activation rates will be more significant.By analyzing the effect of pH on the relationship between phosphorus and selenium,we found that selenium and phosphorus was significantly positively correlated when the pH was at a high level(pH>5.0);When the soil was strongly acidic(pH4.5),selenium and phosphorus was negatively correlated.And the correlation was less significant at the same time.