Soil organic matter clogs mineral pores: evidence from 1H-NMR and N2 adsorption

• Published in: Soil Science Society of America journal Vol. 68; no. 6; pp. 1853 - 1862
• Main Authors: Mikutta, C, Lang, F, Kaupenjohann, M
• Format: Journal Article
• Language: English
• Published: Madison, WI Soil Science Society of America 2004
• Subjects: Agronomy. Soil science and plant productions; Biological and medical sciences; Chemical, physicochemical, biochemical and biological properties; dissolved organic matter; Earth sciences; Earth, ocean, space; Exact sciences and technology; Fundamental and applied biological sciences. Psychology; Geochemistry; minerals; nitrogen adsorption; nuclear magnetic resonance spectroscopy; Organic matter; Physical properties; Physics, chemistry, biochemistry and biology of agricultural and forest soils; polygalacturonic acid; porosity; Soil and rock geochemistry; soil mineral pore clogging; soil organic matter; soil pore system; Soil science; sorption; spectral analysis; Structure, texture, density, mechanical behavior. Heat and gas exchanges; ultrastructure; uronic acids; polygalacturoonic acid; Organic matter; Geochemistry; Plugging; Uronide polymer; Artefact; SOIL CHEMISTRY; Soil science; Method study; dissolved organic matter; Freeze drying; Desiccation; Property of soil; Aluminium Hydroxides oxides; Earth science; Experimental study; Mineral matter; Soils; Analysis method; Nitrogen Molecules; Adsorption; Pore; Macromolecule; Porosity; NMR spectrum; Polysaccharide
• ISSN: 0361-5995; 1435-0661

Recent N2 adsorption studies have suggested a 'pore clogging' effect on mineral soil phases caused by organic matter coatings. For methodological reasons, this pore clogging effect has been studied only after drying. Our hypothesis was that pore clogging is affected by drying of organic coatings. In our study, we used AlOOH, which has been equilibrated with dissolved organic matter (DOM) and polygalacturonic acid [PGA; (C6H8O6)n]. To test our hypothesis, we determined the porosity of moist and freeze-dried AlOOH samples. Freeze-dried samples were analyzed by N2 adsorption, moist samples by 1H-nuclear magnetic resonance (NMR). In addition, the samples were characterized by environmental scanning electron microscopy-energy dispersive x-ray spectroscopy (ESEM-EDX). Both, DOM and PGA significantly reduced specific surface area (SSA(BET)) of AlOOH by 34 m2 g(-1) (15%) and 77 m2 g(-1) (36%). The reduction in SSA(BET) normalized to the amount of C sorbed was 1.0 m2 mg(-1) DOM-C and 5.9 m2 mg(-1) PGA-C. Dissolved OM reduced the pore volume of micro- and small mesopores <3 nm whereas PGA also reduced the volume of larger pores. The 1H-NMR results of moist samples showed that PGA sorption reduced the amount of water in pores <4 nm. In addition, the pore size maximum of AlOOH increased by 150%. Polygalacturonic acid coatings created new interparticle pores of about 10- to 70-nm size that are not stable upon freeze-drying. Porosity changes upon DOM-treatment were not commensurable by 1H-NMR. Our results indicate that clogging of micro- and small mesopores is not an artifact of freeze-drying. Polygalacturonic acid seems not only to cover the mouth of AlOOH-nanometer pores but also to fill them.