|Cassman, Kenneth - UNIV OF NE|
Submitted to: World Congress of Soil Science
Publication Type: Proceedings
Publication Acceptance Date: August 21, 2002
Publication Date: August 21, 2002
Citation: OLK, D.C., CASSMAN, K.G. ORGANIC MATTER QUALITY, NITROGEN CYCLING, AND YIELD TRENDS IN INTENSIVELY CROPPED PADDY SOILS. WORLD CONGRESS OF SOIL SCIENCE. 2002. CD-ROM. BANGKOK, THAILAND. Technical Abstract: Long-term multiple annual cropping of tropical lowland rice has resulted in a decrease in available soil nitrogen (N) and grain yield and an accumulation of soil phenols, which under laboratory conditions chemically stabilize N. In a new field experiment, relationships were quantified between phenols and N cycling for aerobic decomposition of crop residues versus the conventional anaerobic decomposition. During four years, anaerobic decomposition led to gradual enrichment of phenolic compounds and decreased N mineralization during the growing season from one soil organic matter fraction by up to 22 kg N ha**-1, as compared to aerobic decomposition. The inhibition of N mineralization was best correlated with phenol enrichment in mid- to late-season, at high biomass of incorporated crop residues, and after consecutive seasons. **15N-labeled fertilizer was applied at preplant. By harvest, of the **15N that had been immobilized only 8% was remineralized following anaerobic decomposition, but 45% was remineralized following aerobic decomposition. Results suggest that the conventional anaerobic decomposition of crop residues inhibits N mineralization during the growing season and promotes phenol accumulation, which may lead long-term to declining grain yield.