Influences of dissolved organic matter on fluoride fractions in soils
The structure and composition of dissolved organic matter(DOM) extracted from the composted chicken manure were analyzed using elemental composition analysis and Fourier transform infrared spectroscopy(FTIR) methods,and the impacts of this DOM on the fractions of fluoride in soil were analyzed by using sequen-tial extraction procedure and potentiometric analysis methods.The contents of carbon and oxygen were higher than that of hydrogen and nitrogen,accounting for 93% of all the elements in the DOM extracted from composted chicken manure,respectively.Moreover,the carbon and hydrogen saturation was low because of high contents of carboxyl,aldehyde and ketone functional groups in the structure of DOM.As 50%,100% and 200% of DOM added into soil,the contents of water soluble fluoride and available fluoride were declined,and the negative rela-tionship was observed with the increasing dose of exotic DOM amendments in soil.While the concentration of Fe/Mn bound fluoride,organic matter bound fluoride were increased as the same dose of DOM introduced into soil,and the positive relationship was found for the Fe/Mn bound fluoride,organic matter bound fluoride.The exotic DOM may decrease the water soluble and available fractions of fluoride,and increase Fe and Mn bound fluoride,organic matter bound fluoride in tea plantation soil.