Evidence from nuclear magnetic resonance spectroscopy of the processes of soil organic carbon accumulation under long‐term fertilizer management

• Published in: European journal of soil science 2017-09, Vol.68 (5), p.703-715
• Main Authors: Xu, J. S., Zhao, B. Z., Chu, W. Y., Mao, J. D., Olk, D. C., Zhang, J. B., Wei, W. X.
• Format: Article
• Language: English
• Subjects: Abundance; Accumulation; Agricultural land; Agricultural management; Agrochemicals; Aromaticity; Carbon; Carbon 13; Cereal crops; Chemical composition; Corn; Decomposition; Double cropping; Fertilization; Fertilizers; Field tests; Functional groups; Humification; Magnetic resonance spectroscopy; Mineral fertilizers; NMR; Nuclear magnetic resonance; Organic carbon; Organic fertilizers; Organic materials; Organic phosphorus; Organic soils; Oryza sativa; Phosphorus; Potassium; Principal components analysis; Resonance; Rice fields; Soil properties; Spectroscopy; Spectrum analysis; Spinning (materials); Triticum aestivum; Wheat; Zea mays
• ISSN: 1351-0754; 1365-2389
• DOI: 10.1111/ejss.12445

Summary Long‐term application of fertilizers has a considerable effect on the accumulation of soil organic carbon (SOC), but the underlying processes remain unclear. We have examined the effects in the soil of two long‐term (> 20 years) field experiments of a double‐cropped maize (Zea mays L.)–wheat (Triticum aestivum L.) rotation on a Calcaric Fluvisol and paddy rice (Oryza sativa L) on a Hydragric Anthrosol. The chemical structures of the SOC were characterized with multiple cross‐polarization magic‐angle spinning 13C nuclear magnetic resonance spectroscopy. The treatments included organic fertilizer (OF) only, combined NPK (nitrogen, phosphorus and potassium) fertilizer with OF (NPKOF), mineral fertilizer pairings of NPK, NP and NK, and an unamended control. The continuous fertilizer treatments did not change the chemical composition of the Anthrosol SOC greatly except that the NPKOF treatment slightly enriched aromatic C and depleted O–alkyl C compared with the Control. All the treatments on the Anthrosol soil resulted in SOC accumulation, but to different extents. Principal component analysis of the Anthrosol and Fluvisol showed different relationships between the soil properties and functional groups. The Fluvisol SOC decreased in the order balanced fertilizer treatments (OF, NPKOF and NPK), NP, Control and NK treatments. The main structural changes of the Fluvisol SOC followed the same order with a decrease in the abundance of aromatic CO, aromatic C, anomeric C, O–alkyl C and OCH3/NCH, and an increase in COO/NCO and alkyl C, which led to an increase in alkyl–C/O–alkyl–C ratios and a decrease in aromaticity values. These results suggest that SOC accumulation with balanced fertilization on the Fluvisol can be attributed to less decomposition and more humification of the organic materials, whereas the smallest SOC content associated with P omission can be ascribed to more complete decomposition to gaseous end products. We consider that the chemical compositions of SOC may be altered by long‐term fertilizer treatments, depending on the soil type. Highlights How does soil organic carbon (SOC) change in response to long‐term fertilizer management? Improved understanding of SOC accumulation in Fluvisol and Anthrosol agricultural soils. Phosphorus omission in the Fluvisol retarded the accumulation and stimulated the decomposition of SOC. Fertilizer treatments affected chemical composition of SOC of the Fluvisol, but not the Anthrosol.