Full text
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| Author(s): |
Martha González Pérez
Total Authors: 1
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| Document type: | Master's Dissertation |
| Press: | São Carlos. |
| Institution: | Universidade de São Paulo (USP). Instituto de Química de São Carlos (IQSC/BT) |
| Defense date: | 1999-09-28 |
| Examining board members: |
Ladislau Martin Neto;
Júlio César Rocha;
Janete Harumi Yariwake
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| Advisor: | Ladislau Martin Neto |
| Abstract | |
In this work, soil humic acids were characterized, extracted from an Oxisol in Jaboticabal/SP under different management systems: conventional tillage, no-till, and non-cultivated, using EPR, 13C NMR, FTIR, and UV-Vis spectroscopies, as well as elemental analysis. No significant changes were detected in the C, N, H, and O elemental composition of the soil humic acids as a result of different management practices after five years from the establishment of the field experiment. The FTIR spectra of the humic acids were similar for all treatments. Semiquantitative FTIR analysis showed a tendency for decreased COOH and COO- contents under no-till compared to conventional tillage. The higher soil aeration in conventional tillage favored oxidation of humic substances. The level of semiquinone free radicals determined by EPR was approximately 2.37 × 1017 spins/g for humic acids from cultivated soils and 1.02 × 1017 spins/g for humic acids from non-cultivated soil. 13C NMR spectra revealed small qualitative changes in the aliphatic portion of the humic acids due to different management practices, such as an increase in methoxyl and O-aliphatic groups in no-till compared to conventional tillage. The lowest aromaticity percentage and lowest degree of condensation, determined by 13C NMR with dipolar-dephasing, were observed for humic acids from non-cultivated soil. The aromaticity of humic acids from all cultivated treatments was similar, around 25%. These observations are likely associated with the soil type, an Oxisol with high clay content, where the physical protection of organic matter prevents significant structural alterations, even under conventional tillage practices. (AU) | |
| FAPESP's process: | 97/05356-3 - Analises quimicas e espectroscopicas para estudos da materia organica de solos sob diferentes manejos. |
| Grantee: | Martha González Pérez |
| Support Opportunities: | Scholarships in Brazil - Master |