Alberto Vasconcellos Inda

Iron oxides dynamics in a subtropical Brazilian Paleudult under long-term no-tillage management

Replacing conventional tillage (CT) with no-tillage (NT) management alters the pedoenvironment and the rate of topsoil processes, with possible effects on dissolution processes associated with iron oxides and therefore soil mineralogy. This study aimed to determine the effect of NT on the content and distribution of types of iron oxides in a Rhodic Paleudult in southern Brazil. Soil samples were collected at eight depths within the 0.00-0.80 m layer under CT and NT in a long-term experiment (21 years). Mineralogical identification was conducted by X-ray diffraction (XRD), and the Fe content related to specific types of iron oxides determined by selective dissolution and diffuse-reflectance spectroscopy. Kaolinite, quartz, goethite, hematite, and maghemite were identified in the clay fraction. In the NT-managed soil, there was a decrease in the content of crystalline iron oxides and an increase in the content of poorly crystalline iron oxides with increasing proximity to the soil surface. These results suggest that iron oxides are rearranged in this soil by reductive dissolution of the crystalline types and neoformation of metastable ferrihydrite in topsoil layers, which should be assessed further in laboratory studies.

Iron oxides and organic matter on soil phosphorus availability

A continua expansao da producao agricola tem levado a uma crescente demanda de fertilizantes fosfatados. O conhecimento da dinâmica do fosforo no solo e suas interacoes com oxidos de ferro e materia orgânica podem ser uteis no desenvolvimento de estrategias eficientes para o manejo sustentavel, especialmente em um cenario de crescente escassez de fontes de minerais fosfatados. Nesta revisao bibliografica foi abordado a relacao do fosforo com oxidos de ferro e materia orgânica, e seu efeito na disponibilidade de fosforo. As culturas, normalmente, obtem fosfato de minerais intemperizados ou fertilizantes dissolvidos. No entanto, a quantidade de fosforo presente na solucao do solo depende das reacoes de adsorcao e dessorcao por oxidos de ferro, as quais podem ser influenciadas por interacoes com a materia orgânica. Portanto, os sistemas de recomendacao de fertilizantes com base em metodologias que consideram as interacoes entre componentes do solo, tais como oxidos e materia orgânica, e a capacidade de adsorcao de fosforo, resultantes de tais interacoes (por exemplo, analise de P remanescente), pode ser mais confiavel para garantir o uso eficiente e racional de fertilizantes fosfatados.

Estudo comparativo da matéria orgânica de diferentes classes de solos de altitude do sul do Brasil por técnicas convencionais e espectroscópicas

Soils in the region of Campos de Cima da Serra, RS, have high organic matter contents (SOM) and high levels of exchangeable Al. This study aimed to investigate the SOM quality of surface samples (0-10 cm) of eight representative soils from the region (two Neossols, two Gleissols, three Cambissols, one Latosol) under native pasture. The objectives were to evaluate the sample behaviour under demineralization with HF solution, to determine the chemical composition and the influence of exchangeable Al and iron oxides on it. The SOM was concentrated with 10 % (v/v) HF solution and then submitted to elemental analysis, FTIR and 13C NMR CP/MAS spectroscopy. The recovered mass after HF treatment (5.8 to 10 %) was correlated with the soil C content, while the recovered C (47 to 86 %) was inversely correlated with the Fe oxide content. This result indicates that part of the SOM in these soils is associated to these minerals. The proportion of total C O-alkyl groups was high (52 to 59 %) and the values for the I1630/I2920 index (FTIR) were low, evidencing a low humification and decomposition degree of SOM in these soils.

Diffusion and uptake of phosphorus, and root development of corn seedlings, in three contrasting subtropical soils under conventional tillage or no-tillage

Soil mineralogy and management can have substantial effects on phosphorus (P) diffusion in soil and hence on root morphology. The aim of this study was to assess these effects in soils differing widely in P-sorbing components. Samples of a Rhodic Paleudult (RP), a Rhodic Hapludox (RH), and a Humic Hapludox (HH) under conventional tillage (CT) or no-tillage (NT) were placed in Petri dishes to assess P diffusion. Performance and root morphology in corn grown on soil samples subjected to three different P fertilization treatments (no fertilizer, surface, and deep fertilizer application) were examined. Phosphorus diffusion was slower in the HH than in the other soils by effect of its high P adsorption capacity because of its mineralogy. Soil management had no effect on P diffusion. Fertilization with P only affected plant-related variables in RH: surface fertilization increased root biomass, and deep fertilization shoot biomass and proportion of thick roots. Soil management affected plants growing on HH and RP: the plants grown under NT were taller (RP) and developed more fine roots (HH) than those under CT. Fertilization with P had little effect on plant growth in the goethite-rich soil (HH) or the one with high content in available P (RP). Our results suggest that management system in these soils has therefore greater influence on fertility than fertilization treatment.

Chemical and mineralogical changes in a Brazilian Rhodic Paleudult under different land use and managements

Changes in land use and management can affect the dynamic equilibrium of soil systems and induce chemical and mineralogical alterations. This study was based on two long-term experiments (10 and 27 years) to evaluate soil used for no-tillage maize cultivation, with and without poultry litter application (NTPL and NTM), and with grazed native pasture fertilized with cattle droppings (GrP), on the chemical and mineralogical characteristics of a Rhodic Paleudult in Southern Brazil, in comparison with the same soil under native grassland (NGr). In the four treatments, soil was sampled from the 0.0-2.5 and 2.5-5.0 cm layers. In the air-dried fine soil (ADFS) fraction (∅ < 2 mm), chemical characteristics of solid and liquid phases and the specific surface area (SSA) were evaluated. The clay fraction (∅ < 0.002 mm) in the 0.0-2.5 cm layer was analyzed by X-ray diffraction (XRD) after treatments for identification and characterization of 2:1 clay minerals. Animal waste application increased the total organic C concentration (COT) and specific surface area (SSA) in the 0.0-2.5 cm layer. In comparison to NGr, poultry litter application (NTPL) increased the concentrations of Ca and CECpH7, while cattle droppings (GrP) increased the P and K concentrations. In the soil solution, the concentration of dissolved organic C was positively related with COT levels. With regard to NGr, the soil use with crops (NTM and NTPL) had practically no effect on the chemical elements in solution. On the other hand, the concentrations of most chemical elements in solution were higher in GrP, especially of Fe, Al and Si. The Fe and Al concentrations in the soil iron oxides were lower, indicating reductive/complexive dissolution of crystalline forms. The X-ray diffraction (XRD) patterns of clay in the GrP environment showed a decrease in intensity and reflection area of the 2:1 clay minerals. This fact, along with the intensified Al and Si activity in soil solution indicate dissolution of clay minerals in soil under cattle-grazed pasture fertilized with animal droppings.

Atributos químicos e área superficial específica em Latossolo subtropical de altitude sob usos e manejos distintos

The original landscape of Campos de Cima da Serra region has changed by anthropogenic interference. The study aimed to evaluate soil chemical and physical attributes of an Oxisol under natural grassland (CN), burned natural grassland (CNq), natural forest (MN), pine afforestation (PF) and annual crops in conventional tillage system (LA), in the 0.00-0.025, 0.025-0.05, 0.05-0.10, 0.10-0.20, 0.20-0.30m layers. The mineralogy was evaluated by X-ray diffraction. It was evaluated the total organic carbon (TOC); pH (H2O); exchangeable Ca, Mg, K, Na and Al; H+Al and P contents; and calculated bases sum (S), cation exchange capacity (CEC) and bases and Al saturation on CEC. It was estimated soil specific surface area (SSA) and maximum phosphorus adsorption capacity (MPAC). The soil showed kaolinitic and oxidic mineralogy. In the CN soil TOC content ranged between 15.3 and 56.4g kg-1, pH values ≤4.8; CEC was high (18<CECpH7<22 cmolc dm-3) with low bases saturation (3<V<34%) and high Al saturation (23<m<88%). Related to CN soil, TOC contents increased in the MN surface was similar for the CNq and decreased for the FP and LA areas. Soil fertility was positively modified in MN and CNQ areas, and reduced under FP, and was conditioned by TOC. The TOC content was positively related to soil ASE and negatively with soil MPAC.

Caracterização e classificação de solos graníticos em topossequência na região Sul do Brasil

Na regiao sul do Brasil, foi verificada a ocorrencia de forte gradiente textural em solos localizados em areas de morros graniticos. O presente estudo teve como objetivo avaliar os processos pedogeneticos envolvidos na formacao de solos em topossequencia de granito em Porto Alegre (RS). Foram descritos e amostrados morfologica, quimica, fisica e mineralogicamente quatro perfis de solos localizados em diferentes segmentos da paisagem. Os perfis de solos do topo, encosta superior e sope da topossequencia apresentaram gradiente textural expressivo, e a relacao argila fina:argila total aumentou nos horizontes subsuperficias (Bt), indicando transporte da fracao mais fina. O indice de uniformidade inferior a 0,6 sugeriu que os solos nao apresentaram indicios de descontinuidade litologica. O indice Ki, a relacao Fe2O3d/Fe2O3s e a presenca de feldspato e minerais 2:1 e 2:1:1, constatadas pela difracao de raios-x indicaram grau de intemperismo intermediario. A difracao por raios x tambem mostrou aumento do argilomineral caulinita em profundidade. Na encosta inferior, o perfil de solo nao apresentou horizonte B pedogenetico. Os resultados sao indicativos da ocorrencia da lessivagem como o principal processo pedogenetico atuante, apesar das caracteristicas indicativas de estadio de intemperismo pouco avancado.

SOLUBILIZATION OF POTASSIUM FROM ALTERNATIVE ROCKS BY HUMIC AND CITRIC ACIDS AND COFFEE HUSK

O Brasil importa mais de 90% de todo o potassio que consome na agricultura, todavia, essa importacao pode ser minimizada com a utilizacao de fontes alternativas de potassio disponiveis no pais. Nesse contexto, conduziu-se um experimento com o objetivo de avaliar a solubilidade das rochas sienito nefelinico e glauconita em funcao do emprego de tres diferentes matrizes orgânicas: acidos humico, acido citrico e casca de cafe. O experimento foi realizado em laboratorio, sendo adotado o delineamento inteiramente casualizado. Cada rocha foi misturada com cinco doses diferentes de cada matriz orgânica e as avaliacoes dos teores de K solubilizado foram realizadas, periodicamente, durante 180 dias. O teor de potassio soluvel foi determinado em funcao do emprego de solucao de acido citrico a 2% e agua, na fase de extracao. Independentemente da matriz orgânica e de sua dose, o sienito nefelinico libera mais K que a glauconita. O K solubilizado aumenta com o acrescimo do tempo de incubacao e sua liberacao e maior, a medida que se eleva a dose da matriz orgânica. Ha maior solubilizacao de K quando a palha de cafe e misturada as rochas potassicas em relacao aos acidos humico e citrico.

CHARACTERIZATION AND CLASSIFICATION OF FLOODPLAIN SOILS IN THE PORTO ALEGRE METROPOLITAN REGION, RS, BRAZIL

In the Porto Alegre metropolitan region (PAMR) there are a significant proportion of floodplain soils, mainly Planosols and Gleysols, in relation to upland soils. This study aimed to evaluate the morphological, chemical and physical characteristics, and to classify floodplain soils in the PAMR. Six soil profiles were evaluated under different sedimentary lithologies and drainage classes, and samples were collected for chemical and physical analyzes. Two orders of mineral soils (Planosols and Gleysols) and one order of organic soil (Organosols) were identified. The soils were moderately deep to deep and stratified. In mineral soils hue ranged between 7.5YR and 2.5Y, with the occurrence of Bg, Btg or Cg gley horizons, while in organic soil the colors were neutral. Sand and silt were the predominant particle sizes according to the origin sedimentary deposits. The organic carbon content was negatively related to soil density and positively related to soil specific surface area and with soil cation exchange capacity. Soil chemical characterization showed expressive variation in bases, aluminum and sodium saturation. Ki index and Fe(CBD)/Fe(H2SO4) ratio indicated a low soil weathering degree. The different sedimentary lithologies and the soil hydromorphism degree were the main factors related to differences in morphological, physical and chemical characteristics of soils in the PAMR.

Óxidos de ferro e área superficial de Latossolo subtropical sob campo e floresta nativa

The current weather conditions indicate a substitution of grassland by forest vegetation in the Campos de Cima da Serra in Rio Grande do Sul, Brazil. This change in vegetation changes the contents of soil organic matter and soil moisture. This study aimed to evaluate the pedogenetic iron oxides in an Oxisol under native forest and grassland and its relationship with soil total organic carbon content and soil specific surface area. Replacing grassland with native forest resulted in an accumulation of soil organic carbon and possibly influenced dissolutive processes of crystalline iron oxides types and neoformation of metastable types of low crystallinity. In native forest soil, the increase of total organic carbon increased the soil specific surface area, masking the positive effect of iron oxides on this physical characteristic.