Nitrogen-bonded aromatics in soil organic matter and their implications for a yield decline in intensive rice cropping

Previous research has shown that long-term intensive cropping of irrigated lowland rice has led to significant grain-yield declines in field trials. The yield decline was attributed to decreased availability of soil nitrogen, which is held mostly in the soil organic matter. By advanced solid-state N...

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Bibliographic Details
Published in:Proceedings of the National Academy of Sciences - PNAS 2004-04, Vol.101 (17), p.6351-6354
Main Authors: Schmidt-Rohr, K, Mao, J.D, Olk, D.C
Format: Article
Language:English
Subjects:
Acid soils
Agricultural production
Agriculture
Anilides
Arid zones
Biological Sciences
Carbon
Crops
Lignin
Nitrogen
Organic soils
Rice
Rice soils
Soil organic matter
Soils
Spiders
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Summary:Previous research has shown that long-term intensive cropping of irrigated lowland rice has led to significant grain-yield declines in field trials. The yield decline was attributed to decreased availability of soil nitrogen, which is held mostly in the soil organic matter. By advanced solid-state NMR spectroscopy, we have detected significant amounts of amide nitrogen directly bonded to aromatic rings in a humic acid fraction extracted from a continually submerged, triple-cropped rice soil. Because nitrogen bonded to aromatics is not readily plant-available, this observation can explain the yield decline. Quantitative 13 C NMR combined with advanced spectral editing showed that this humic acid is rich in lignin derivatives (>45% of all carbon), whereas the corresponding humic acid fraction extracted from an aerobic, single-cropped rice soil contains less lignin and less nitrogen bonded to aromatics.
ISSN:0027-8424
1091-6490
DOI:10.1073/pnas.0401349101