The effects of land-use type on water-extracted organic matter (WEOM) concentration and composition and their spectral characteristics were investigated. Soil samples were collected across the Loess Plateau, which included 19 cropland samples (CL), 14 abandoned samples (AL), 10 grassland samples (GL), 5 forest samples (FR), and 4 orchard samples (Orch). The average WEOC concentration varied from 289.0 to 362.2 mg kg-1 among different land-use types, and there was no significant difference in WEOC content in topsoils (P ≤ 0.05). The amounts of four components identified by the EEM-PARAFAC method were in the order of C1 > C3 > C2 > C4 in all soils. The two humic acid-like components (C1 and C3) were the dominant fractions of WEOM in topsoils in the Loess Plateau area, irrespective of land-use types. The study showed that the EEM fluorescence spectroscopy can be successfully used to characterize WEOM fractions in soils. Our results showed that land-use type has no effects on WEOC concentration in topsoils. Humic acid-like substances dominated in the measured WEOM fractions, while the humic acid-like substances (C1) in Orch soils are the highest and fulvic acid-like and protein-like substances exist a relatively high content in GL soils.
Keywords: EEM-PARAFAC; Land use; Water-extracted organic carbon; Water-extracted organic matter.