PEDOGÊNESE E MATÉRIA ORGÂNICA DE SOLOS ...

PADDY SOILS UNDER DIFFERENT USES 1/
Author: Luís de França da Silva Neto
Advisor: Prof. Dr. Alberto Vasconcellos Inda Junior
Co-advisor: Prof. Dr. Paulo César do Nascimento
ABSTRACT
Paddy soils of Porto Alegre region are intensively used in agriculture,
showing social, economic and environmental importance. The aim of this work
was study pedogenetic and management aspects of paddy soils by the
evaluation of morphological, physical and chemical soil characteristics,
structural composition and physical and chemical fractions of soil organic matter
(SOM). We collected samples of six paddy soil profiles, four of these with two
distinct use or management. In the first study we study morphological, physical
and chemical soil characteristics, including sulfuric acid attack and iron oxides
selective dissolutions. In the second study, were determined the total organic
carbon (TOC), carbon of physical and chemical SOM fractions, and the
structural composition and humification degree of SOM through laser induced
fluorescence spectroscopy (LIF), Fourier transformed infra-red (FTIR) and solid
state 13 C nuclear magnetic resonance spectroscopy ( 13 C NMR). Paddy soils
showed differences due to pedogenetic and variations due to management
processes. The high value of silt/clay, subsurface high activity clay and high ki
indicated a low soil weathering degree. The pH, TOC, base saturation,
hidromorfic degree and particle-size distribution were more sensible to soil
management induced alterations, influencing the soil classification. The TOC
content was inferior in intensive managed soils, constituting an impact in soil
quality and environment. The SOM physical fractions distribution was altered by
the soil management, with particulate organic carbon associated to rice
cultivation. The SOM chemical fractions distribution showed humin
predominance in all the soils, and low weight carbon and humic acids in
intensive managed soils. The results showed great association of SOM
structural aspects with pedogenesis. Within the same soil, different uses (cover
crop, management system and fertilization practices) changed the structural
composition of SOM. The humification degree evaluate by LIF and the index of
decomposition by 13 C NMR varied according environment of soil, and were
higher in intensive managed paddy soils.
1/ Doctoral thesis in Soil Science. Programa de Pós-Graduação em Ciência do Solo,
Faculdade de Agronomia, Universidade Federal do Rio Grande do Sul. Porto Alegre.
(109 p.) September, 2010. Financial support by CAPES, CNPq and FAPERGS.
vii