|Cassman, K - U. OF NEBRASKA, AGRO&HORT|
Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: May 15, 2003
Publication Date: N/A
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.