title: Direct estimation of nitrate, total and fractionated water extractable organic carbon (WEOC) in an agricultural soil using direct UV absorbance deconvolution.
abstract: In this study, a multiwavelength UV spectral deconvolution (UVSD) procedure is proposed as a robust and simple procedure for direct estimation of carbon and nitrate contents in soil water extracts. Soil samples were collected from an open-air field cultivated with maize at 3 different depths, 30cm each, between 0 and 90cm of soil surface during a period of 7 months. Fractionation of water extractable organic carbon (WEOC) into hydrophobic (Hpo-WEOC), transphilic (Tpi-WEOC), and hydrophilic (Hpi-WEOC) fractions is performed using XAD-8 and XAD-4 resins connected in series. In order to perform UVSD, 3 representative reference spectra of WEOC fractions were selected automatically, in addition to a 4th spectrum representative of NO(3)(-) selected manually in order to compose the deconvolution basis. The restitution of UV spectra was made in the range 235-350nm. Through exploitation of soil water extract UV spectra, it was possible in a single-step deconvolution procedure to determine the organic carbon (mg Cl(-1)) and NO(3)(-) (mg l(-1)) concentrations and to differentiate and to quantitatively estimate carbon content of WEOC fractions. Statistical tests indicated satisfactory correlations between values estimated using UVSD and those determined by conventional reference methods for each parameter determined. The ranges of concentrations of carbon and NO(3)(-) in the soil water extracts studied are between 3.00 and 15.00mg Cl(-1) and 60-300mg l(-1), respectively. The limits of quantification (LQ) and of detection (LD) of WEOC and NO(3)(-) were found to be 0.10 and 0.05mg Cl(-1), and 0.10 and 0.03mg l(-1), respectively.
authors.affiliation: LCE, Université de Provence, 3, Place Victor Hugo, Case 29, 13003 Marseille Cedex 03, France. mohammad.hassouna@up.univ-mrs.fr
authors.forename: Mohammad
authors.initials: M
authors.lastname: Hassouna
authors.forename: Frédéric
authors.initials: F
authors.lastname: Theraulaz
authors.forename: Catherine
authors.initials: C
authors.lastname: Massiani