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Multinuclear Magnetic Resonance Analysis of Two Humic Acid Fractions from Lowland Rice Soils

^a Department of Chemistry, Queen Mary, University of London, London E1 4NS, UK
^b International Rice Research Institute, DAPO Box 7777, Metro Manila, Philippines

View larger version (45K): [in a new window]   Fig. 1. Carbon-13 cross polarization and magic angle spinning (CPMAS) with total suppression of sidebands (TOSS) nuclear magnetic resonance (NMR) spectra of mobile humic acids (MHA) and calcium humates (CaHA) from four soils varying in intensity of irrigated rice cropping: maize (MHA, 2.4 h; CaHA, 3.1 h); rice–soybean (MHA, 2.4 h; CaHA, 2.2 h); Bicol Integrated Agricultural Research Center (BIARC) control (MHA, 2.6 h; CaHA, 6.9 h); and Long-Term Continuous Cropping Experiment (LTCCE) control (MHA, 0.9 h; CaHA, 2.4 h).

View larger version (41K): [in a new window]   Fig. 2. Means and standard errors of spectral proportions of C functional groups.

View larger version (37K): [in a new window]   Fig. 3. Solid-state 13C cross polarization and magic angle spinning (CPMAS) with total suppression of sidebands (TOSS) (dotted line) and dipolar dephasing (DD)–TOSS (full line) spectra of mobile humic acids (MHA) and calcium humates (CaHA) from one soil with no annual irrigated rice crops (dryland rice) and one soil with three irrigated rice crops per year (Long-Term Continuous Cropping Experiment [LTCCE] Control).

View larger version (40K): [in a new window]   Fig. 4. Nitrogen-15 cross polarization with magic angle spinning (CPMAS) nuclear magnetic resonance (NMR) spectra of mobile humic acids (MHA) and calcium humates (CaHA) from four soils varying in intensity of irrigated rice cropping: maize (MHA, 17.5 h; CaHA, 21.6 h); rice–soybean (MHA, 24.3 h; CaHA, 22.7 h); Bicol Integrated Agricultural Research Center (BIARC) control (MHA, 21.9 h; CaHA, 25.3 h); and Long-Term Continuous Cropping Experiment (LTCCE) control (MHA, 19.1 h; CaHA, 21.9 h). A line broadening of 100 Hz was applied. Spinning sidebands can occur at positions marked .

View larger version (32K): [in a new window]   Fig. 5. Means and standard errors of spectral proportions of N functional groups.

View larger version (34K): [in a new window]   Fig. 6. Solution 31P nuclear magnetic resonance (NMR) spectra of the mobile humic acids (MHA) and calcium humates (CaHA) from the maize field and the control (no fertilizer) treatment at the International Rice Research Institute (IRRI) Long-Term Fertility Experiment (LTFE) site. A line broadening of 10 Hz was applied. No peaks were found outside the depicted regions.

View larger version (32K): [in a new window]   Fig. 7. Means and standard errors of spectral proportions of P functional groups.