[Effect of pH on the Ultraviolet Spectra and Fluorescence Characteristics of Dissolved Organic Matter in the Process of Straw Humification].

Crop straw is the dominant by-product from agriculture and is regarded as the new source of non-point contamination. Straw incorporation is possible to solve the issues of straw reduction and reutilization, which is clearly required in the twelfth five-year-plan for national economic and social development of the People's Republic of China. At present, it is of noticeable lack of the investigation on straw incorporation behavior and detail humification product analysis in the representative regions under different environmental conditions. The ultraviolet and fluorescence spectrometry were used to reveal the characteristics of dissolved organic matter (DOM), affected by pH values, in the straw humification process in loess region. The results showed: the ultraviolet absorbance of DOM samples increased firstly and then decreased with the increasing wavelength from 200 to 700 nm, and the maximum absorbance peaks appeared around the wavelength of 240 nm. The maximum absorbance peaks (λmax) were greater at pH values of 6, 8 and 9 than that of 7, and the low degree of humification was indicated from the values of SUVA254, E3/E4 and A253/A203, caused by the short period of humification. The fluorescence peaks of extracted DOM from loess appeared around the regions of λ(dx/em) = 250/330 and λ(ex/em) = 325/450, referred as UV fulvic-like fluorescence, and visible fulvic-like and humic-like fluorescence, respectively. The increasing pH values resulted in the greater wavelength of absorbance peak, suggesting the increased aromaticity and conjugated degree, and the novel fluorescence peak was found in λ(ex/em) = 250/450. The pH values were more effective to change the UV fulvic-like fluorescence peaks intensity (increased firstly and then decreased) than that of visible fulvic-like and humic-like fluorescence, which might be related to buffer effect, fluorescence quenching (side effects) and component structure. The ultraviolet and fluorescence spectrometry were acceptable to illustrate the characteristics variation of DOM affected by pH values in the straw humification process.