Organic N forms of a subtropical Acrisol under no-till cropping systems as assessed by acid hydrolysis and solid-state NMR spectroscopy |
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| Authors: | Jeferson Dieckow João Mielniczuk Heike Knicker Cimélio Bayer Deborah P Dick Ingrid Kögel-Knabner |
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| Institution: | (1) Embrapa Instrumentação Agropecuária, P.O.Box 741, São Carlos, SP, 13.560-970, Brazil;(2) Departamento de Solos, Faculdade de Agronomia, Universidade Federal do Rio Grande do Sul, P.O. Box 15100, Porto Alegre, RS, 91.501-970, Brazil;(3) Lehrstuhl für Bodenkunde, Technische Universität München, Freising-Weihenstephan, 85350, Germany;(4) Departamento de Físico-Química, Instituto de Química, Universidade Federal do Rio Grande do Sul, Porto Alegre, RS, 90.001-970, Brazil |
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| Abstract: | This study was conducted to investigate the influence of land-use systems (grassland and cropland) and of long-term no-till cropping systems bare soil, oat/maize (O/M), pigeon pea+maize (P+M)] on the composition of organic N forms in a subtropical Acrisol. Soil samples collected from the 0- to 2.5-cm layer in the study area (Eldorado do Sul RS, Brazil) were submitted to acid hydrolysis and cross-polarization magic angle spinning (CPMAS) 15N and 13C nuclear magnetic resonance (NMR) spectroscopies. The legume-based cropping system P+M contained the highest contents of non-hydrolysable C and N, hydrolysable C and N, amino acid N and hydrolysed unknown N. The relative proportion of non-hydrolysable N was higher in bare soil (30.0%) and decreased incrementally in other treatments based on the total C and N contents. The amino acid N corresponded to an average of 37.2% of total N, and was not affected by land use and no-till cropping systems. The non-hydrolysable residue contained lower O-alkyl and higher aromatic C concentrations, as revealed by CPMAS 13C NMR spectroscopy, and higher C:N ratio than the bulk soil. No differences in the bulk soil organic matter composition could be detected among treatments, according to CPMAS 13C and 15N NMR spectra. In the non-hydrolysable fraction, grassland showed a lower concentration of aromatic and a higher concentration of alkyl C than other treatments. From CPMAS 15N NMR spectra, it could be concluded that amide N from peptide structures are the main organic N constituent. Amide structures are possibly protected through encapsulation into hydrophobic sites of organic matter and through organomineral interaction. |
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| Keywords: | No tillage Organic N Acid hydrolysis Amino acids Solid-state 15N NMR spectroscopy |
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