Species Of Fluorine In Tea Garden Soils And Methodology Of Reducing Soil Water Soluble Fluorine Content

Tea is an important source for people to intake fluoride, which, with a right amount, is helpful for avoiding dental caries and strengthening bone tissue, but, with an excessive amount, is harmful by causing irreversible damage, such as joint pain, limited mobility, humpbacked, lame and so on. Fluorine in tea maily comes from soil. There have been many reports about contents of fluorine in tea garden soils and the cumulative distribution of tea fluoride. But there have been few reports about the form distribution of fluorine in soil and the correlation between floride in tea and fluorine in soil. Fluorine adsorbed by tea plants is of the water-soluble fluorine, which is the hub of soil, water, plant and animal for fluorine circulation. Consequently, it has theoretical and practical significance to study the distribution of fluorine in soil and methodology of reducing soil water soluble fluorine content for improving the quality of tea, decreasing contents of fluoride in tea and ensuring health of human.Taking 14 tea leave samples and the 14 corresponding soils of tea gardens in Hubei province as research objects, this study researched the content of fluorine in tea, distribution of fluorine in soil and the relationship between the distribution of fluorine in soil and the physical-chemical properties of soils. Calcium-containing materials(CaCO3, CaO, Ca3(PO4)2, CaCl2, CaSO4), solid sorbent(active carbon, zeolite, diatomite) and biomass materials(loquat and bamboo leaves) were used to regulate water-soluble fluoride in tea garden soils collected from Yingshan, Dawu, Zhushan, Chibi of Hubei province and Hangzhou of Zhejiang province.The content of fluorine in Hubei tea leaves varied from 321 to 2274 mg/kg for old leaves and from 57 to 1806 mg/kg for young leaves. The content of fluorine in old leaves was higher than that in young leaves, which shows that the accumulation of fluorine in old leaves increased significantly. The total fluorine decreased with the increased soil depth, but the content of other forms of fluorine changed with the increase of soil depth. The content of fluorine in different layers of soils were all in the order of residual F (Res-F)>>rganic bound F (Or-F)>Fe(Mn) oxides bound F (Fe/Mn-F)>water soluble F (Ws-F)>extractable F (Ex-F), and the residual fluorine is the main form in tea garden soils. Total F (T-F) was positively correlated with total phosphorus at a statistically significant level. Ws-F was positively correlated with pH, CEC and exchangeable Ca content significantly. Ex-F was positively correlated with clay content, CEC, free Al and free Fe contents. Fe/Mn-F was positively correlated with pH, contents of exchangeable Ca and total phosphorus, but it was negatively correlated with contents of amorphous Al and free Al significantly. Or-F was positively correlated with contents of exchangeable Ca and total phosphorus. The different form of fluorine was not significantly correlated with organic matter and amorphous Fe.The results indicated that the content of water-soluble fluoride in soils of Yingshan, Dawu and Zhushan decreased after application of CaCl2 and CaSO4, and the effect of applying CaCl2 was better than that of CaSO4. However, the content of water-soluble fluoride in these three soils increased by applying CaCO3, CaO or Ca3(PO4)2. The appropriate amount was 1～2 g/kg of CaCl2 or CaSO4 in soils of Yingshan and Dawu, and 3～5 g/kg of CaCl2 or CaSO4 in the soil of Zhushan, respectively. The content of water-soluble fluoride in soils of Chibi and Hangzhou decreased by applying CaCO3, CaO or Ca3(PO4)2, and the appropriate amount for soil of Chibi was 1.5～2 g/kg of CaCO3 or CaO or 3-4 g/kg of Ca3(PO4)2, while for the soil of Hangzhou was 4-5 g/kg of CaCO3, CaO or Ca3(PO4)2. The effect of applying CaCO3 was better than that of CaO and Ca3(PO4)2 on the soils of Chibi and Hangzhou, however, the content of water-soluble fluoride in these two soils increased by applying CaCl2 or CaSO4. The content of water-soluble fluoride in soils of Yingshan, Dawu, Zhushan, Chibi and Hangzhou increased by applying activated carbon, zeolite, diatomite, loquat or bamboo leaves, so these can not be applicable.