Flávio Adriano Marques

Relationship between soil oxidizable carbon and physical, chemical and mineralogical properties of umbric ferralsols

SUMMARY The occurrence of Umbric Ferralsols with thick umbric epipedons (≥ ≥ ≥ ≥ 100 cm thickness) in humid Tropical and Subtropical areas is a paradox since the processes of organic matter decomposition in these environments are very efficient. Nevertheless, this soil type has been reported in areas in the Southeast and South of Brazil, and at some places in the Northeast. Aspects of the genesis and paleoenvironmental significance of these Ferralsols still need a better understanding. The processes that made the umbric horizons so thick and dark and contributed to the preservation of organic carbon (OC) at considerable depths in these soils are of special interest. In this study, eight Ferralsols with a thick umbric horizon (UF) under different vegetation types were sampled (tropical rain forest, tropical seasonal forest and savanna woodland) and their macromorphological, physical, chemical and mineralogical properties studied to detect soil characteristics that could explain the preservation of high carbon amounts at considerable depths. The studied UF are clayey to very clayey, strongly acidic, dystrophic, and Al-saturated and charcoal fragments are often scattered in the soil matrix. Kaolinites are the main clay minerals in the A and B horizons, followed by abundant gibbsite and hydroxyl-interlayered vermiculite. The latter was only found in UFs derived from basalt rock in the South of the country. Total carbon (TC) ranged from 5 to 101 g kg -1 in the umbric epipedon. Dichromateoxidizable organic carbon represented nearly 75 % of TC in the thick A horizons, while non-oxidizable C, which includes recalcitrant C (e.g., charcoal), contributed

Assessment of carbon storage under rainforests in Humic Hapludox along a climosequence extending from the Atlantic coast to the highlands of northeastern Brazil

An understanding of the stock of soil organic carbon (SOC) in the umbric epipedon of Oxisols located in the tropical forests surrounded by a semi-arid region is limited but essential because of their importance in the global cycle of carbon (C). The purpose of this study was to assess the effects of climatic (temperature and rainfall), soil organic matter (SOM) composition and litter on the stability of C in surfaces and subsurfaces in five Humic Oxisols along a 475-km climosequence from 143 to 963ma.s.l. in a tropical environment in northeastern Brazil. We assessed vertical changes in SOC; soil total nitrogen (N); C from the microbial biomass; δ(13)C, δ(15)N and the humified composition of SOM; the composition of the humin (HUM) fraction by Fourier Transform Infrared (FTIR); and Thermogravimetry (TG) and Differential Scanning Calorimetry (DSC) at depth. The elemental and isotopic composition of the litter samples were analyzed in all areas studied. The results indicated that the current climate and recalcitrant organic compounds are not preponderant factors in the formation of the umbric epipedon, as suggested by the partial influence of temperature and rainfall on SOM. In addition, SOM was dominated by easily decomposable compounds, as indicated by the predominance of aliphatic C-H groups in the HUM fraction in the FTIR spectra; by the thermal oxidation through DSC-TG, which revealed that approximately 50% of the HUM was composed easily decomposable compounds; and by the high proportion of organic C present in the microbial biomass. Values of δ(13)C showed a predominance of C3 plant-C in SOM whereas δ(15)N patterns indicated that N dynamics differ among the profiles and drive the accumulation of C. These findings can help to characterize the susceptibility of these soils to changes in climate and land use and the implications for the sequestration of soil C.

Caracterização de vertissolos da ilha de Fernando de Noronha, Pernambuco

O Arquipelago de Fernando de Noronha (FN) possui solos pouco desenvolvidos das classes dos Cambissolos, Vertissolos e Neossolos, com caracteristicas peculiares relacionadas ao material de origem vulcânico, clima tropical com franco dominio oceânico e relevo ondulado a forte ondulado. Os Vertissolos de FN sao formados a partir de rochas basicas, tufos vulcânicos e sedimentos aluvionares e estao associados as superficies rebaixadas com drenagem impedida do planalto central ou da baixada litorânea. Tendo em vista a necessidade de preservacao ambiental, uso agricola ou geotecnico e caracteristicas peculiares desse ambiente insular, os Vertissolos de FN precisam de melhor entendimento de seus atributos. O objetivo deste trabalho foi, portanto, caracterizar morfologica, fisica, quimica e mineralogicamente Vertissolos de ocorrencia comum na ilha de Fernando de Noronha. Tres perfis de Vertissolos derivados de diferentes materiais de origem, classes de drenagem e niveis de salinidade e sodicidade foram descritos e coletados para realizacao das analises de caracterizacao. Os solos estudados foram: Vertissolo Haplico ortico solodico (P01), Vertissolo Haplico salico gleissolico (P02) e Vertissolo Haplico sodico gleissolico (P03). Os Vertissolos de FN apresentam feicoes tipicas da ordem, como a textura argilosa a muito argilosa, as superficies de friccao (slickensides) e o fendilhamento horizontal e vertical quando secos. Esses solos sao imperfeitamente a maldrenados e sofrem alagamento temporario no periodo de maior concentracao das chuvas. Apresentam elevados valores de soma e saturacao por bases, alem de teores altos a muito altos de P extraivel, de distribuicao irregular entre perfis e com dominância de formas inorgânicas. Nao obstante, esses apresentam problemas de acumulacao de sais, o que restringe a utilizacao agricola ou geotecnica deles. Os principais minerais da fracao argila dos solos sao do grupo das esmectitas, seguidos por caulinitas e, ou, haloisitas. A fracao silte e constituida por hematita, goethita, magnetita/maghemita, ilmenita, mica e feldspato e por minerais pouco comuns em solos brasileiros como crandalita e holandita.

FRAÇÕES HUMIFICADAS DA MATÉRIA ORGÂNICA EM FUNÇÃO DO CULTIVO DE COQUETÉIS VEGETAIS

The aim of this study was to assess the organic matter changes in quantity and quality, particularly of the humic fraction in the surface layer (0–20 cm), of a Typic Plinthustalf soil under different management of plant mixtures used as green manure for mango (Mangifera indica L.) crops. The plant mixtures, which were seeded between rows of mango trees, were formed by two groups of leguminous and non -leguminous plants. Prior to sowing, seeds were combined in different proportions and compositions constituting the following treatments: 100% non-leguminous species (NL); 100% leguminous species (L); 75% L and 25% NL; 50% L and 50% NL; 25% L and 75% NL; and 100% spontaneous vegetation, considered a control. The plant mixtures that grew between rows of mango trees caused changes in the chemical composition of the soil organic matter, especially for the treatments 50% L and 50% NL and 25% L and 75% NL, which increased the content of humic substances in the soil organic matter. However, the treatment 25% L and 75% NL was best at minimising loss of total organic carbon from the soil. The humic acids studied have mostly aliphatic characteristics, showing large amounts of carboxylic and nitrogen groups and indicating that most of the organic carbon was formed by humic substances, with fulvic acid dominating among the alkali soluble fractions.