Submitted to: American Chemical Society National Meeting
Publication Type: Abstract Only
Publication Acceptance Date: March 27, 2003
Publication Date: March 27, 2003
Citation: SCHMIDT-ROHR, K., MAO, J., OLK, D.C. CHARACTERIZATION OF SOIL ORGANIC MATTER IN TROPICAL RICE SOILS BY ADVANCED SOLID-STATE NMR. AMERICAN CHEMICAL SOCIETY NATIONAL MEETING. 2003. PAPER NO. GEOC-058.
The chemical structures of soil organic matter in a continually submerged, triple-cropped lowland rice soil having large inputs of rice straw and an aerobic dryland rice soil were compared using advanced solid-state nuclear magnetic resonance (NMR) techniques. Quantitative 13C NMR shows that a humic acid (HA) fraction extracted from the triple-cropped rice soil was rich in lignin derivatives (ca. 45% of carbon) but nearly free of charcoal. Significant amounts (35%) of nitrogen bonded to aromatic rings were detected by 14N-13C NMR. The 13C and 15N chemical shifts and relatively high NCO:NCH ratio indicated NCO bonded to aromatic rings. In contrast, the corresponding HA fraction of the dryland soil with lower lignin input showed predominantly NCO and NCH signals of easily degradable peptides and heterocyclic N. Nitrogen species bonded to aromatics are considered as not readily plant-available, and their accumulation coincides with a substantial long-term grain yield decline in the lowland rice field.