A long-term effect of N fertilization on the 13C CPMAS NMR of de-ashed soil humin in a second-growth Douglas-fir stand of coastal British Columbia

摘要: Abstract Carbon-13 CPMAS NMR spectroscopy was used to examine long-term effects of thinning and N fertilization on the humin fraction soil organic matter in a second-growth Douglas-fir stand coastal British Columbia. De-ashed organic-matter-enriched fractions were prepared from three mineral horizons four silvicultural treatments using 1.0 M HF accompanied by magnetic stir bar remove ferromagnetic iron particles, followed density separation. With some exceptions higher proportion mass recovered denser, light-coloured fraction, C less-dense, dark fraction. In all cases, less-dense enriched total compared original crude humin, had more favourable C/Fe ratio for spectroscopy. The observable 33–37% 8 samples, but as low 7.6% remaining four. spectra typical features humins (alkyl C, O-alkyl di-O-alkyl aromatic carboxyl, ester amide C). fertilization, there small consistent decrease alkyl regardless horizon or thinning, indicating lower extent decomposition. subspectra based proton spin relaxation time ( T 1 H ) obtained one fertilized unfertilized sample. Subspectra slowly-relaxing (long domain dominated long-chain C. For sample, subspectrum fast-relaxing (short )) O- with results normal spectra. Despite uncertainties introduced de-ashing treatment 13C showed that has effect which is reflected this