Composition of organic matter fractions for explaining wettability of three forest soils

• Published in: Soil Science Society of America journal Vol. 69; no. 1; pp. 57 - 66
• Main Authors: Ellerbrock, R.H, Gerke, H.H, Bachmann, J, Goebel, M.O
• Format: Journal Article
• Language: English
• Published: Madison Soil Science Society 01.01.2005; Soil Science Society of America; American Society of Agronomy
• Subjects: Aggregates; Agronomy. Soil science and plant productions; Biological and medical sciences; Cambisols; Cations; Chemical, physicochemical, biochemical and biological properties; Earth sciences; Earth, ocean, space; Exact sciences and technology; Forest soils; Fundamental and applied biological sciences. Psychology; genetic soil types; Hydrophilic surfaces; Organic carbon; Organic chemistry; Organic matter; Physical properties; Physics, chemistry, biochemistry and biology of agricultural and forest soils; Podzols; Soil organic matter; Soil science; Soil sciences; Soil types; soil wettability; Soils; Surficial geology; Water and solute dynamics; wettability; Organic matter; Cambisols; Property composition relationship; Property of soil; Forest soil; Earth science; Physical properties; Wettability; Soil water properties; Podzols; Surface properties; Soil science; Chemical composition; Chemical properties; Loamy sand soil
• ISSN: 0361-5995; 1435-0661; 1435-0661
• DOI: 10.2136/sssaj2005.0057

Soil organic matter (SOM) as a solid or as a film at mineral surfaces affects wetting properties in unsaturated soil. Soil organic matter mostly consists of a heterogeneous mixture of components with hydrophilic and hydrophobic functional groups. This paper analyzes relations of SOM to soil wettability by considering functional group compositions of different soluble fractions. Forest soil samples from two loamy sand Cambisol profiles (locations Chorin and Steigerwald) and from a Podzol (Waldstein) were used to obtain water SOM(W) and sodium pyrophosphate SOM(PY) soluble SOM fractions. The hydrophobic (A) and hydrophilic (B) functional groups of bulk soil SOM and of the soluble fractions were evaluated using transmission Fourier-transform infrared (FT-IR) spectroscopy. Advancing liquid-solid contact angles (CA) were determined by using the capillary rise method. For soil organic carbon (SOC) contents <10 g kg(-1), wettability increased with SOC content while it decreased for SOC contents >10 g kg(-1). Although hydrophilic groups in FT-IR spectra of SOM(W), SOM(PY), and bulk soil dominated (i.e., A/B ratios between 0.08 and 0.5), soil wettability was reduced (i.e., CA between 88 and 52 degrees). Soil specific relations between CA and A/B ratios could be obtained after introducing relatively soil type independent factors, G. As exponential functions of the SOC/clay relation, the G-factors imitate the effectiveness of functional groups with respect to wettability. The results suggest that in addition to SOC content, the SOM composition may improve explanations of soil wettability if the spatial orientation of SOM functional groups at the SOM-mineral surface in the presence of sorption sites and polyvalent cations is considered.