Influence And Mechanisms Of Amendments On Selenium Availability In Highy Acidic Se-rich Soil Of Tea Garden

We took sampling survey,incubation experiment and field trail to inhibit further soil acidification and improve chemical and biological availability of selenium(Se)in local highly acidic Se-rich soil,making Se-rich tea without adding exogenous Se,thus ensuring the safety and quality of Se source for people.The main findings in this study are as follows:First,we took sampling survey in North Zhejiang and the region of Yixing and Liyang.The results showed that:the local typical teagarden soil existed serious phenomenon of acidification.All the soil of teagarden is highly acidic soil.The range of pH is 3.89 to 5.03,lower than the optimal pH 5.5 for tea treegrowth.Among them,the proportion of soil pH value of tea garden that lower than the minium for tea treegrowth was up to 60%.The range of total Al is 72.40-136.59g/kg,and the exchangeable Al is within the range from 184.70 to 875.34 mg/kg.More than 90%of aluminum is in the form of low activity state or residual state in the soil.Total Se content ranges from 0.32 to 1.00 mg/kg in the surface of soil,68.75%of teagarden soil Se in Se-rich level.The content of available Se is in the range of 8.20 to 91.05?g/kg,account for 1.46 to 14.59%of total Se,which shows that Se potential utilization rate is higher.The content of total Se has significantly positive correlation with available Se and soluble form,exchangeable and carbonate bound forms and organic bound form of Se.The content of available Se has significantly positive correlation with soluble form,exchangeable and carbonate bound forms and organic bound form of Se.The value of pH has significantly negative correlation with available Se and soluble Se.The content of organic matter has negative correlation with oxide-bound form Se and positive correlation with other forms of Se.Heavy metals have different correlation with Se.Chromium has significant assorted relation with Se.Cadmium,copper and lead have certain associated relations with Se.Arsenic has antagonistic effect with Se.A series of incubation experiment were carried out to study the effects and mechanisms of three amendments(straw charcoal,calcium-magnesium phosphate and earthworm liquid fertilizer)and their different applying modes on Se availability of highly acidic Se-rich soil in teagardens.The results showed that the effect of calcium-magnesium phosphate on the validity of Se is more outstanding compared with straw charcoal and earthworm liquid fertilizer.All treatments improved the content of available Se significantly.The effect of combined treatment is better than single treatment,and the treatment that applied straw charcoal and calcium-magnesium phosphate at the same time worked most effectively.All treatments improved the content of soluble Se significantly,but decreased organic bound Se.It was found that Se transformed from organic bound form to soluble form.The mechanisms to improve the availability of selenium in soil are neutralizing acidic soil and P-Se interaction.Morphological analysis showed that Al transformed from exchangeable form to organic complexed form,which promotes Se transformed from organic bound form to soluble form,thus improving the content of available Se,and enhancing the chemical availability of selenium in soil.Field trail set three different applying modes of straw charcoal,calcium-magnesium phosphate with earthworm liquid fertilizer timing staggered,in order to study the effects on soil acidification,Se availability,Se content in tea and tea quality.The results showed that three applying modes can effectively improve soil physical and chemical properties,increase soil fertility,enhance the activity of selenium element.Compared with the contract,soil pH,organic matter,available phosphorus and CEC were increased significantly in the treatments of C-B,P-B and PC-B.The treatment that applied straw charcoal and calcium-magnesium phosphate at the same time with earthworm liquid fertilizer timing staggered worked most effectively.Different applying modes remarkably improved the chemical and biological availability of Se and the tea quality.Compared with the contact,the treatments of C-B,P-B,PC-B respectively increased the content of available Se in soil by 15.4,19.3 and 25.1?g/kg,content of Se in tea 30.1,57.6 and 58.5?g/kg,Calcium 196.53,108.93and 249.04 mg/kg,zinc 2.26,3.30 and 2.26 mg/kg.Three treatments decreased Al in tea by 23.05,23.05 and 38.13 mg/kg,respectively.