Banca de DEFESA: OTAVIO AUGUSTO QUEIROZ DOS SANTOS

Uma banca de DEFESA de DOUTORADO foi cadastrada pelo programa.
STUDENT : OTAVIO AUGUSTO QUEIROZ DOS SANTOS
DATE: 15/09/2025
TIME: 14:00
LOCAL: Defesa on line
TITLE:

Soil organic matter management in tropical conditions: impacts on carbon, soil properties, bacterial diversity, and greenhouse gas emissions.

KEY WORDS:

Soil organic matter; drainage, climate change, greenhouse gas emissions, soil microbiology

PAGES: 111
BIG AREA: Ciências Agrárias
AREA: Agronomia
SUBÁREA: Ciência do Solo
SPECIALTY: Gênese, Morfologia e Classificação dos Solos
SUMMARY:

Histosols are recognized as important global carbon reservoirs, but their conversion to agricultural systems generally requires drainage and liming, practices that can accelerate the degradation of soil organic matter (SOM) and increase greenhouse gas (GHG) emissions. This study evaluated the combined effects of long-term management and drainage on SOM dynamics, soil attributes, microbial diversity, and GHG fluxes in an Histosols from southeastern Brazil. Field assessments, conducted in Histosols with different land uses—cassava (Manihot esculenta) monoculture for 80 years, cassava–coconut (Cocos nucifera) intercropping for 20 years, and a forest fragment in natural regeneration for 20 years—showed significant reductions in labile and humified SOM fractions under continuous cultivation, while only recalcitrant structures remained in the regenerating area. Solid-state spectroscopic analyses (UV-vis, ATR-FTIR, and 13C NMR) confirmed these structural changes. In laboratory experiments, liming significantly increased CO2 emissions, regardless of the drainage level, with estimated losses of 4.1 Mg ha-1 in the first incubation phase and 1.6 Mg ha-1 in the second. A reduction in fulvic and humic acid contents was also observed, indicating degradation of humic fractions. Another drainage experiment, conducted in PVC columns, showed that intensive drainage reduced pH (from 5.2 to ~4.0), promoted carbon losses, and increased CO2 emissions, while less drainage preserved carbon but favored CH4 emissions due to methanogenesis. Less drained environments also showed greater bacterial diversity, highlighting the influence of oxygenation on microbial structure. Overall, the results demonstrate that management intensity and drainage regimes strongly affect SOM stability and the GHG balance in Histosols. Intermediate water table levels may represent a sustainable compromise, balancing SOM conservation and the mitigation of CO2 and CH4 emissions.

COMMITTEE MEMBERS:
Presidente - 1060711 - MARCOS GERVASIO PEREIRA
Externo ao Programa - 2136627 - NIVALDO SCHULTZ - UFRRJExterno à Instituição - ARCANGELO LOSS - UFSC
Externo à Instituição - DAVID VILAS BOAS DE CAMPOS
Externo à Instituição - GUSTAVO SOUZA VALLADARES - UFPI