Characterization of Water Extracts of Two Manures and Their Adsorption on Soils

Abstract To uncover possible chemical differences between stockpiled and composted dairy manures, water extracts of these manures were analyzed by 13 C nuclear magnetic resonance (NMR) and by pyrolysis‐field ionization mass spectrometry (Py‐FIMS). Judging from the 13 C NMR, which took into consideration all of the organic C present, aliphatic and aromatic C in the composted and stockpiled manure extracts were similar but the composted manure extract appeared to be richer in protein C, phenolic C, and carboxylic C and poorer in carbohydrate C than the stockpiled manure extract. Major components of the extract of the stockpiled manure extract determined by Py‐FIMS, which measured only volatile organics, were N compounds > phenols + monolignins > carbohydrates > alkylaromatics > peptides = lipids > lignin dimers > sterols > fatty acids > suberins. On the other hand, the quantitative order of organic components of the composted manure extract was phenols + monolignins > N compounds > carbohydrates > peptides > alkylaromatics > lipids > fatty acids > sterols = lignin dimers > suberins. The relatively low total ion intensity of the water extract of the composted manure and its greater aromaticity suggested that composting increased polymerization and cross‐linking and so led to the formation of larger molecules. Water‐soluble organic C (DOC) extracted from the manures was used to study adsorption isotherms on soils varying in clay content from 3 to 54%. The adsorption of the DOC by the soils increased as the clay and organic matter contents and the surface areas of the soils increased. Increased adsorption of the DOC extracted from the composted manure appeared to be due to increased molecular weights of the major DOC components.