Acidic Properties of Plant Lignins and Humic Materials of Soils

Abstract

The acidic properties of lignins from the native vegetation of a virgin Ella loamy sand and the humic acids, the I, 4-dioxane extractable humic fraction and residual humic acids from the virgin and cultivated soils were investigated by determining solid-state cation exchange capacities for Cu and Ca and by nonaqueous potentiometric titration, using potassium methoxide in a benzenemethanol mixture as titrant. The lignins and soil dioxane extracts were titrated in pyridine; the humic acids in dimethylformamide. Platinized Pt and CHIOH modified calomel electrodes formed the electrode combination.The CEC of the humic acids were much higher than the CEC of lignins with both cations but the Cu:Ca absorption ratios were less for humic acids than for lignins. Titration curves of lignins showed two potential breaks with total acidities of 960 to 1,190 me/Ioo g. Titration curves of the humic acids showed three to six potential breaks while curves of the soil dioxane extracts showed three and four. The total acidities of the two types of humic isolates were 1,100-1,200 me/roo g. The equivalent weights of most lignins and humic materials were very similar although the acid groups might be different with respect to types and acid strength. Lignins from other plant materials and humic isolates from other soils were also investigated by non-aqueous titration to determine the general applicability of the results obtained with isolates from the Ella soils.

Alkaline Cupric Oxide Oxidation of Roots and Alkaline-Extractable Organic Matter of Chernozemic Soils

“…(.1971) (Craggs et al 1914) and the phenol depolymerization technique (Piper and Posner 1975 (Herman et al l91l). However, the differential nature of these roots may have to be considered when determining degrees of humification (Lutwick and Dormaar 1976 Thompson (1965) and humic substances extractable with chelating resin wete obtained as outlined by Dormaar (1974).…”