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Characterization of Humic Acid from No‐Tilled and Tilled Soils Using Carbon‐13 Nuclear Magnetic Resonance
Author(s) -
Stearman G. K.,
Lewis R. J.,
Tortorelli L. J.,
Tyler D. D.
Publication year - 1989
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj1989.03615995005300030018x
Subject(s) - humic acid , chemistry , soil water , decomposition , fertilizer , composition (language) , carbon fibers , carbon 13 nmr , environmental chemistry , nuclear chemistry , organic chemistry , geology , soil science , materials science , linguistics , philosophy , composite number , composite material
Chemical composition of humic acids is important due to their reactivity with soil‐applied pesticides and fertilizer amendments. Humic acids from continuously (7 yr) no‐tilled and tilled cotton, corn, and soybean plots in West Tennessee were characterized by 13 C‐NMR from soils sampled at various depths. Humic acids were extracted with dilute NaOH solution and purified with KOH‐KCL and HCL‐HF solution, respectively. NMR solution spectra generated on a Jeol FX 90Q spectrometer (Jeol Co., Tokyo, Japan) were divided into six regions (0–40, 40–62, 62–105, 105–150, 150–170, and 170–190 ppm) and peak areas compared. Humic acid composition differed by soil depth and crop. Small differences were observed between tillage systems. Aliphatic and aromatic carbons ranged from 48 to 65% and 25 to 40% of total peak area, respectively. Carboxyl groups of humic acids as determined by 13 C‐NMR ranged from 9 to 13%. Humic acids extracted from those soils containing larger amounts of C (surface no‐tilled treatments) had greater aliphatic to aromatic ratios, perhaps due to earlier stages of decomposition.