ABSTRACT Understanding organic carbon and predominant humic fractions in the soil allows contributes to soil quality management. Conventional fractionation techniques require time, excessive sampling, and high maintenance costs. In this study, predictive models for organic carbon in humic substances (HS) were evaluated using hyperspectral data as an alternative to chemical fractionation and quantification by wet digestion. Twenty-nine samples of Neossolos Flúvicos (Fluvents) - A1, and 36 samples of Cambissolos (Inceptisols) - A2 were used. The samples were also analyzed jointly, creating a third sample group - A1&A2. Untransformed spectral reflectance factors were obtained using the FieldSpec Pro FR 3 hyperspectral sensor (350–2500 nm). Pre-processing techniques were employed, including Savitzky–Golay smoothing and first- and second-order derivative analysis. After selecting variables using the Backward method, which removes spectral variables that are not statistically significant for the regression. Estimation models were built by Principal Components Regression (PCR) and Partial Least Squares Regression (PLSR). The spectral data were evaluated individually for soil classes A1 and A2, and jointly for A1&A2. The PLSR was more efficient than PCR, especially for the estimation models that used the first derivative of reflectance employing the three sample groups. For samples of A1, the best estimate was seen for humic acid (RPD = 6.09) and humin (RPD = 2.38); for A2, the best models estimated the OC in fulvic acid (RPD = 2.35) and humin (RPD = 2.51); and for the joint spectral data (A1&A2), the prediction was robust for humin only (RPD = 2.01). The most representative wavelengths were observed using the first derivative with PLSR and PCR, centred on the region between 1600 and 1800 nm. The first-derivative of reflectance calculated more-robust predictive models using PLSR than PCR. The best predictions occurred for organic carbon associated with humic acid in Neossolos Flúvicos, with fulvic acid in Cambissolos, and with humin in both soil classes.

ABSTRACT The rational exploitation of the land requires planning its agricultural use, which can be supported by the agricultural land suitability (ALS) assessment. The scheme to assess ALS proposed by Food Agricultural Organization (FAO) has been adopted in Brazil based on guiding charts for subtropical, humid tropical and semi-arid tropical climate. However, the guiding chart used for the semi-arid region has dramatically limited the ALS in drylands on which rainfed agriculture has been practiced. In this study, an adequation for the ALS assessment regarding the edaphoclimatic conditions of semi-arid region was proposed to improve the representation of agricultural areas and to allow a better planning of soil conservation practices. The ALS of the south region of Ceará State (Brazil) was assessed according to the FAO scheme and its initial adaptation to the Brazilian conditions; subsequently, this assessment was obtained by two adequations. Adequation I disregarded the limiting factor of water availability, while adequation II, besides disregarding the factor of water availability, established new limits for the classes of effective soil depth. The adequations resulted in an increase of 177.19 % in the areas with regular suitability for crops to the detriment of areas with restricted suitability for crops and areas with suitability only for pasture or grazing lands. The adequations increased the agricultural suitability in 41.26 % of the area of the mapping units, and 16.77 % of them were due to the modifications related to the effective soil depth, while the other 26.35 % were due to the changes related to water availability. The results related to water availability were equivalent to those observed through the dynamic analysis of land-use and cover associated with the rainfall, which demonstrated an increase in the areas for rainfed agriculture and a reduction in fallow and pasture areas in the years with rainfall within the climatic normality. The areas considered suitable for crop production with the adequation of the scheme may be included in soil conservation programs.

RESUMO A compactação modifica o arranjo estrutural e as funções essenciais dos poros do solo. O trabalho teve como objetivo avaliar o impacto de diferentes graus de compactação em um Argissolo Amarelo sobre os atributos físicos-hídricos indicadores da funcionalidade dos poros. Foram utilizados cilindros de solo 0.05 x 0.05 m em 4 graus de compactação (GC): 61, 71, 82 e 92%, e em cada GC, foi quantificado, sob um delineamento inteiramente aleatorizado, a distribuição de poros por tamanho, permeabilidade intrínseca do solo ao ar (Kar), índice N de continuidade de poros, curva caraterística da água no solo e frequência acumulada de poros. O incremento no GC não causou impacto na quantidade de microporos, mas diminuiu a quantidade de macroporos para valores menores que o mínimo requerido a partir do GC de 82%. O aumento no CG provocou redução no índice N, Kar e porosidade de aeração, porém com amplitude diferente dependendo do GC e da tensão da água no solo. Os GC acima de 61% reduziram o conteúdo de água na faixa de tensão entre 0 até 6 kPa e, como consequência, aumentaram a porcentagem de poros de areação; enquanto na faixa entre 10 e 1500 kPa proporcionaram maior retenção de água. A avaliação dos atributos físicos-hídricos do Argissolo Amarelo revelou que o incremento na compactação alterou a estrutura do solo, reduziu e formou poros pouco contínuos, e menos permeável ao fluxo de ar; e apesar da maior retenção de água nas tensões mais elevadas, promoveu menor conteúdo de umidade disponível.

ABSTRACT Compaction modifies the structural arrangement and essential functions of soil pores. In this context, the objective of this study was to evaluate the impact of different compaction levels in an Argissolo Amarelo (Ultisol) on the physical-hydraulic attributes that indicate the functionality of soil pores. The experiment was conducted using 0.05 x 0.05 m soil cylinders with 4 compaction levels (CL): 61, 71, 82 and 92%, and at each CL, the pore-size distribution, intrinsic soil air permeability (Kair), pore continuity index N, soil water characteristic curve and cumulative pore-size frequency were quantified under a completely randomized design. The increase in CL did not impact the amount of micropores, but reduced the amount of macropores to values lower than the minimum required from the CL of 82%. The increase in CL caused reductions in N index, Kair and aeration porosity, but with different amplitude depending on the CL and the water tension in the soil. CL above 61% reduced the water content at the tension range between 0 and 6 kPa and, as a consequence, increased the percentage of aeration pores, besides promoting greater water retention within the range between 10 and 1500 kPa. The evaluation of the physical-hydraulic attributes of the Argissolo Amarelo (Ultisol) revealed that the increase in the compaction level altered soil structure, reduced and formed pores that were poorly continuous and less permeable to air flow and, despite the higher water retention at the higher tensions, promoted lower available moisture content.

RESUMO O processo de desertificação causa redução da vegetação e degradação do solo. A ausência de técnicas de visualização e ampla dimensão espaço - temporal dos dados dificultam a identificação da desertificação e a rápida tomada de decisão por equipes multidisciplinares. O Scatter Plot 2D é uma análise visual e bidimensional das reflectâncias das bandas do vermelho (630 - 690 nm) e do infravermelho próximo (760 - 900 nm) para visualizar a resposta espectral da vegetação. Nesse sentido, a hipótese deste trabalho é que a visualização das reflectâncias da vegetação através do Scatter Plot 2D permitirá inferir a ocorrência de desertificação. Neste estudo o objetivo foi identificar áreas desertificadas e caracterizar a dinâmica espacial e temporal da vegetação e do solo nos períodos secos (FS) e chuvosos (FC), de 2000 a 2008 usando o Scatter Plot 2D. Foram utilizados o 2D Scatter Plot do Envi® 4.8 e as reflectâncias das bandas 3 e 4 do sensor TM5 em comunidades do núcleo de Irauçuba (Ceará, Brasil). Foram observadas as densidades de concentração das reflectâncias dos pixels de vegetação em relação ao infravermelho próximo. Todas as comunidades em todos os períodos de avaliação apresentaram concentrações de pixels com reflectâncias inferiores a 0,4 (40%), indicando pouco desenvolvimento da vegetação e posterior degradação, causadas pelo desmatamento, uso do fogo e sobre pastejo. Portanto o Scatter Plot 2D foi capaz de mostrar a vegetação com baixas reflectâncias no infravermelho próximo entre os anos de 2000 a 2008 em épocas secas e chuvosas, permitindo inferir a ocorrência da desertificação.

ABSTRACT The desertification process causes soil degradation and a reduction in vegetation. The absence of visualisation techniques and the broad spatial and temporal dimension of the data hampers the identification of desertification and rapid decision-making by multidisciplinary teams. The 2D Scatter Plot is a two-dimensional visual analysis of reflectances in the red (630 - 690 nm) and near-infrared (760 - 900 nm) bands to visualise the spectral response of the vegetation. The hypothesis of this study is that visualising the reflectances of the vegetation by means of a 2D scatter plot will allow desertification to be inferred. The aim of this study was to identify desertified areas and characterise the spatial and temporal dynamics of the vegetation and soil during dry (DP) and rainy (RP) periods between 2000 and 2008, using a 2D scatter plot. The 2D scatter plot generated by the Envi® 4.8 software and the reflectances in bands 3 and 4 of the TM5 sensor were used within communities in the Irauçuba hub (Ceará, Brazil). The concentration densities of the near-infrared reflectances of the vegetation pixels were observed. Each community presented pixel concentrations with reflectances of less than 0.4 (40%) during each of the periods under evaluation, indicating little vegetation development, with further degradation caused by deforestation, the use of fire and overgrazing. The 2D scatter plot was able to show vegetation with low reflectance in the near infrared during both dry and rainy periods between 2000 and 2008, thereby inferring the occurrence of desertification.

RESUMO A região semiárida do nordeste brasileiro possui mais de 53 milhões de habitantes que dependem, direta ou indiretamente, dos recursos que a região oferece. Dentre esses recursos, o solo é destacado como um dos mais importantes. Em função da importância atribuída ao conhecimento das características pedológicas e morfológicas dos solos do semiárido do nordeste brasileiro, o presente estudo teve como objetivo identificar e caracterizar as diferentes classes de solo existentes na Fazenda Experimental Lavoura Seca, no município de Quixadá, Ceará, por meio do método tradicional de mapeamento de solos. O local selecionado localiza-se no município cearense de Quixadá, com uma extensão total de aproximadamente 190 hectares. Foi estabelecida uma grade regular de 200 m x 200 m para determinação dos locais de amostragem, totalizando 47 pontos de coleta. As amostras de solo foram coletadas com trado nas profundidades 0-20, 40-60 e 80-100 cm, procedendo-se, posteriormente, as análises químicas e granulométricas para seleção dos locais de abertura das trincheiras e classificação das unidades taxonômicas segundo o Sistema Brasileiro de Classificação de Solos (SIBCS). As classes de solos predominantes na área de estudos foram: Neossolos Litólicos Eutróficos típicos (60%), Planossolos Háplicos Eutróficos típicos (20%), Argissolos Vermelhos Eutróficos típicos e abrúpticos (16%) e Luvissolos Crômicos Órticos típicos (4%). As diferenças no material de origem, no relevo e no clima foram os principais fatores influenciadores para a ocorrência de uma diversidade de classes de solo na área estudada, apresentando grandes extensões de solos jovens e rasos, bem como solos evoluídos e profundos.

ABSTRACT The semiarid region of northeastern Brazil has more than 53 million inhabitants who depend, directly or indirectly, on the resources that the region offers. Among these resources, the soil is highlighted as one of the most important. Due to the importance attributed to the knowledge on the pedological and morphological characteristics of the soils of the Brazilian northeastern semiarid region, the aim of this study was to identify and characterize the different soil classes on the Lavoura Seca Experimental Farm, in the municipality of Quixadá, Ceará, Brazil, through the traditional method of soil mapping. The selected site is located in the municipality of Quixadá, Ceará, with a total extension of approximately 190 hectares. A regular grid of 200 m x 200 m was established to determine the sampling sites, totaling 47 collection points. The soil samples were collected with an auger at depths of 0-20, 40-60 and 80-100 cm, and the chemical and granulometric analyses were then carried out to select the pit opening sites and classify the units according to the Brazilian Soil Classification System (SIBCS). The predominant soil classes in the study area were: Neossolos Litólicos Eutróficos típicos (59.4%), Planossolos Háplicos Eutróficos típicos (20.4%), Argissolos Vermelhos Eutróficos típicos and abrúpticos (15.9%) and Luvissolos Crômicos Órticos típicos (4.3%). Differences in parent material, relief and climate were the main influencing factors for the occurrence of a diversity of soil classes in the studied area, which shows large extensions of young and shallow soils, as well as evolved and deep soils.

ABSTRACT: Knowledge of the hydraulic properties of the soil is of crucial importance to an understanding of the interactions between vegetation, soil and water. There is little information available about the hydraulic properties of Podzol soils found in tropical regions. The aim of this study was to present the soil morphology and hydraulic properties of a toposequence situated in a permanent plot at the Ilha do Cardoso State Park (Cananéia, SP, Brazil). Ultradetailed soil maps were used to define a toposequence inside the permanent plot. Five profiles, representing the main types of soil, were opened along the toposequence, in which Podzols are dominant. The levels of bulk density, sand content, porosity and permeability in these soils were all high. Consequently, these soils have a high level of hydraulic conductivity with low water retention. This behavior undergoes an alteration in the Bh and Bs horizons due to the accumulation of organic and metallic compounds and a changing structure that modifies the pore distribution. Furthermore, the characterization of the hydro-physical functioning of soils in natural environments is an important source of encouragement to further investigative study of soil water dynamics and its relationship to the native vegetation.

ABSTRACT When the harvesting of sugarcane involves a mechanized process, plant residues remain on the soil surface, which makes proximal and remote sensing difficult to monitor. This study aimed to evaluate, under laboratory conditions, differences in the soil spectral behavior of surface layers Quartzipsamment and Hapludox soil classes due to increasing levels of sugarcane’s dry (DL) and green (GL) leaf cover on the soil. Soil cover was quantified by supervised classification of the digital images (photography) taken of the treatments. The spectral reflectance of the samples was obtained using the FieldSpec Pro (350 to 2500 nm). TM-Landsat bands were simulated and the Normalized Difference Vegetation Index (NDVI) and soil line were also determined. Soil cover ranged from 0 to 89 % for DL and 0 to 80 % for GL. Dry leaf covering affected the features of the following soil constituents: iron oxides (480, 530 and 900 nm) and kaolinite (2200 nm). Water absorption (1400 and 1900 nm) and chlorophyll (670 nm) were determinant in differentiating between bare soil and GL covering. Bands 3 and 4 and NDVI showed pronounced variations as regards differences in soil cover percentage for both DL and GL. The soil line allowed for discrimination of the bare soil from the covered soil (DL and GL). High resolution sensors from about 50 % of the DL or GL covering are expected to reveal differences in soil spectral behavior. Above this coverage percentage, soil assessment by remote sensing is impaired.

O estudo da dinâmica da água no solo utilizando topossequências é de grande importância para melhor compreender as relações solo-água-vegetação. Objetivou-se, com este trabalho, caracterizar físico, hídrica e morfologicamente os solos da mata do Parque Estadual de Carlos Botelho. A parcela abrange uma área de 10,24 ha (320 x 320 m), localizada sob Floresta Ombrófila Densa (Mata Atlântica de Encosta). Com base nos mapas de solos ultradetalhados e mapas planialtimétricos dessa área, escolheu-se uma transeção representativa dos solos da parcela; nessa, foram abertas cinco trincheiras, onde foi feita a descrição morfológica dos diferentes horizontes dos solos. No estudo da dinâmica da água no solo, foram feitas análises granulométricas, de densidade do solo e partículas, de curvas de retenção e de medidas de condutividade hidráulica saturada no campo, utilizando-se o permeâmetro de Guelph. Coletaram-se amostras indeformadas para realizar análises de imagens. Os Cambissolos apresentaram-se como os solos predominantes na parcela, mas também foram encontradas manchas de Neossolos e Gleissolos. No estudo da caracterização físico-hídrica dos solos da topossequência escolhida, observou-se mudança na condutividade hidráulica entre as camadas superficiais e subsuperficiais, de alta/intermediária para intermediária/baixa permeabilidade. Essa variação do comportamento da água no solo também pôde ser observada nas curvas de retenção de água, que evidenciou maior retenção de água nos horizontes subsuperficiais. Fatores como porosidade total, dimensão, forma e conexão entre os poros foram analisados por meio da análise de imagens. O comportamento físico-hídrico dos solos foi influenciado pelas características morfogênicas do solo.

Studies of soil-water dynamics using toposequences are essential to improve the understanding of soil-water-vegetation relationships. This study assessed the hydro-physical and morphological characteristics of soils of Atlantic Rainforest in the Parque Estadual de Carlos Botelho, state of São Paulo, Brazil. The study area of 10.24 ha (320 x 320 m) was covered by dense tropical rainforest (Atlantic Rainforest). Based on soil maps and topographic maps of the area, a representative transect of the soil in this plot was chosen and five soil trenches were opened to determine morphological properties. To evaluate the soil hydro-physical functioning, soil particle size distribution, bulk density (r), particle density (r s), soil water retention curves (SWRC), field saturated hydraulic conductivity (Ks), macroporosity (macro), and microporosity (micro) and total porosity (TP) were determined. Undisturbed samples were collected for micromorphometric image analysis, to determine pore size, shape, and connectivity. The soils in the study area were predominantly Inceptisols, and secondly Entisols and Epiaquic Haplustult. In the soil hydro-physical characterization of the selected transect, a change was observed in Ks between the surface and subsurface layers, from high/intermediate to intermediate/low permeability. This variation in soil-water dynamics was also observed in the SWRC, with higher water retention in the subsurface horizons. The soil hydro-physical behavior was influenced by the morphogenetic characteristics of the soils.

The study of the hydro-physical behavior in soils using toposequences is of great importance for better understanding the soil, water and vegetation relationships. This study aims to assess the hydro-physical and morphological characterization of soil from a toposequence in Galia, state of São Paulo, Brazil). The plot covers an area of 10.24 ha (320 × 320 m), located in a semi-deciduous seasonal forest. Based on ultra-detailed soil and topographic maps of the area, a representative transect from the soil in the plot was chosen. Five profiles were opened for the morphological description of the soil horizons, and hydro-physical and micromorphological analyses were performed to characterize the soil. Arenic Haplustult, Arenic Haplustalf and Aquertic Haplustalf were the soil types observed in the plot. The superficial horizons had lower density and greater hydraulic conductivity, porosity and water retention in lower tensions than the deeper horizons. In the sub-superficial horizons, greater water retention at higher tensions and lower hydraulic conductivity were observed, due to structure type and greater clay content. The differences observed in the water retention curves between the sandy E and the clay B horizons were mainly due to the size distribution, shape and type of soil pores.

Os fatores limitantes do ambiente físico do Cerrado têm sido muito discutidos. Porém, o detalhamento da morfologia do solo torna-se fundamental à compreensão do seu funcionamento físico-hídrico e sua relação com a paisagem. O objetivo deste estudo foi relacionar os atributos macro e micromorfológicos à retenção de água no solo em uma toposseqüência sob cerradão em uma parcela permanente de 320 <FONT FACE=Symbol>´</FONT> 320 m, instalada em Assis, SP. Amostras coletadas em cinco pontos distribuídos na toposseqüência foram utilizadas para determinar a macroporosidade do solo por análise de imagens, porosidade total estimada, análise química, granulometria e retenção de água no solo. De montante a jusante, os solos foram classificados como Latossolo Vermelho, Latossolo Vermelho-Amarelo, Latossolo Amarelo e Gleissolo Háplico, apresentando uma transição gradual de cor e textura franco-arenosa. No horizonte de superfície, o maior teor de matéria orgânica e a elevada macroporosidade total determinaram menor densidade do solo e baixa retenção de água. Nos Latossolos, a microestrutura do solo consistiu principalmente em aglomerados de microagregados, ocasionando uma elevada macroporosidade no horizonte diagnóstico. No Gleissolo, a menor porosidade total nos horizontes mais profundos resultou em uma maior retenção de água e drenagem imperfeita. As diferenças morfológicas de cor e estrutura do solo foram influenciadas pelas condições de retenção de água na vertente. A baixa retenção de água nos horizontes de solo superficiais e latossólicos, condicionada pela elevada macroporosidade total, é um dos fatores que pode definir o padrão vegetacional de cerradão na parcela permanente.

The limiting factors of the Brazilian savanna physical environment have been largely discussed. Soil morphology is fundamental to understand the behavior of soil water flow, soil physical properties and soil-landscape relationships. The aim of this study is to relate soil micro and macromorphologic attributes to soil water retention on a toposequence under native savanna woodland (cerradão) in a permanent plot of 320 m <FONT FACE=Symbol>´</FONT> 320 m installed in Assis, SP, Brazil. Samples collected at five points within the toposequence were used to determine the soil macroporosity by means of image analyses, estimated total porosity, chemical analysis, particle size distribution analysis and soil water retention. From the summit down to the footslope, the soils were classified as Rhodic Haplustox, Typic Haplustox and Epiaquic Haplustult, presenting a gradual color transition and a sandy loam texture. In the surface horizons, the higher organic matter content and the high total macroporosity determined a lower soil bulk density and lower water retention. In the Oxisols, the high soil macroporosity results from the packing of microaggregates in the oxic horizon. In the Ultisol, the lower total porosity in the deeper horizons resulted in a higher water retention and an imperfect water drainage. The water retention conditions on the slope influenced the morphological differences in soil color and structure. The low water retention on the surface and oxic horizons, conditioned by the high total macroporosity, is one of the factors that may define the vegetal pattern of the savanna woodland within the permanent plot.