Submitted to: American Geophysical Union
Publication Type: Abstract Only
Publication Acceptance Date: October 20, 2004
Publication Date: December 18, 2004
Citation: Olk, D.C. 2004. Chemical stabilization of soil organic nitrogen by phenolic lignin compounds in anaerobic agrosystems [CD-ROM]. American Geophysical Union. Paper No. 5896. Washington, D.C.
In tropical Asia, continuous cropping of paddy rice promotes the covalent binding of soil organic nitrogen (N) by phenolic lignin residues, which in turn appears to contribute to substantial long-term declines in the availability of soil organic N and grain yield. A newly developed technique of nuclear magnetic resonance spectroscopy that selects for carbon atoms bound to N was applied to a young humic fraction to directly observe an agronomically significant greater quantity of organic N (difference of 55 kg per hectare) that was bound by lignin residues in a triple-cropped rice soil compared to a nearby aerated soil. The resulting compound was an anilide. Crop residues are the parent material of soil organic matter in agricultural soils, and their anaerobic decomposition was found to slow microbially driven mineralization of both soil organic N and soil phenols during the rice season, compared to aerobic decomposition. Through use of 15N-labeled fertilizer, stabilization of soil organic N was shown to be more extensive than binding of inorganic fertilizer N. Similar results were gained in eastern Arkansas when comparing a more anaerobic continuous rice rotation to the conventional rice-soybean rotation. Future studies of covalently bound N will consider both its seasonal dynamics and its significance to long-term yield trends. Agronomic observations suggest that covalent binding of nutrients by lignin residues might also occur in other agrosystems with anaerobic decomposition of crop residues, including paddy taro in Hawaii and to a lesser extent no-tilled crops in regions with cool, wet springtime weather.