Fig. 2From: Separation of acid-soluble constituents of soil humic acids by dissolution in alkaline urea solution and precipitation with acidlog(A 400/A 600) versus A 600/C diagram of precipitated and DAX-8-adsorbed fractions. The symbols (A, B, P, and Rp) in the figure indicate the types of HAs in Kumada’s classification system [20]. The degree of humification is higher in the order A > B or P > Rp Back to article page