ABSTRACT Bulk density (BD) is a soil physical property used as a soil quality indicator and variations in this measurement influence soil water content and carbon stock estimates. This study aims to compile a database of samples of bulk density, textural fractions, and organic carbon values, as well as evaluate the accuracy of published pedotransfer functions (PTF) that predict bulk density, and propose a hierarchical PTF to predict the bulk density of Brazilian Soils. The performance of eleven PTFs and the newly proposed PTFs were evaluated and compared using the root mean square error (RMSE) and coefficient of determination (R2) based on a testing soil database collected from the literature. We noticed a slight improvement in accuracy when organic carbon and coarse and fine sand fractions were included as predictors alongside silt and clay. The best results with existing PTFs were obtained by PTF-A in Tomasella and Hodnett (1998) (RMSE = 0.20 g cm–3) and PTF-F in Benites et al. (2007) (RMSE = 0.17 g cm–3). Our proposed PTFs use textural fractions and organic carbon as predictors in a hierarchical form. The proposed PTF-4, which uses fine sand, coarse sand, clay, and organic carbon, presented the lowest value for RMSE (0.14 g cm–3) for BD prediction.

ABSTRACT Chemical soil analysis data can be expressed by weight (i.e., gravimetric basis) or volume (i.e., volumetric basis) of the fine earth (sieved ≥2 mm), resulting in different units, cmolc kg-1 and cmolc dm-3, respectively. The research problem is that the difference between methods to express the same soil properties hinders the comparison of results and database or dataset standardization. This paper aims to develop pedotransfer functions (PTF) to obtain the density of fine earth, which will then be used for conversion data expressed in volumetric to gravimetric basis, or vice versa, that will be applied to compare results and to standardize databases with different units. Soils samples, including profiles of the main soil orders in Brazil such as Latossolos (Ferralsols or Oxisols) and Argissolos (Acrisols or Ultisols), from the states of Rondônia, Roraima, and Mato Grosso do Sul (132 horizons) were selected and weighed (in triplicate) to obtain the fine earth mass contained in a volume of 10 cm3. The mass values were used to calculate the fine earth density. Spearman’s correlation analysis was used between the density and nine soil properties (coarse sand, fine sand, total sand, silt, clay, clay dispersed in water, clay dispersion, particle density, and organic carbon). The total sand, clay, and organic carbon showed the best correlations, therefore they were selected to construct the pedotransfer functions. Nonlinear regression techniques were used to obtain the models (PTFs) to predict density, which was used for unit conversion. As a result, the residual standard error (RSE) statistics of the models were: 0.0920, 0.1231, and 0.1633 g cm-3, respectively for PTF1 (using total sand as a predictor), PTF2 (using clay), and PTF3 (using organic carbon). Independent data was used to evaluate the accuracy of the models by residue analysis and the RSE. For the validation, the lowest RSE obtained was from the PTF1, so the best performance. Thus, to convert values of the chemical properties from a volumetric to gravimetric basis, the value must be divided by the predicted density. While, the conversion from gravimetric to volumetric basis requires that the value be multiplied by the predicted density. The PTFs using the properties total sand, clay, and organic carbon as predictor variables, allowed conversion of analytical data of soil samples expressed in the volumetric basis to gravimetric and vice versa, which can be used for dataset or database standardization.

A matéria orgânica tem importante papel em diversas propriedades do solo e por isso é necessário identificar sistemas de manejo do solo que favoreçam seu aumento e, ou, mantenham suas concentrações. Este estudo teve como objetivo determinar a qualidade e quantidade de C orgânico em diferentes compartimentos da fração do solo, em diversos ecossistemas amazônicos. Fracionou-se a matéria orgânica do solo e estimou-se os estoques de C em floresta primária (FP), pastagem (P), sucessão secundária (SS) e sistema agroflorestal (SAF). As amostras foram coletadas em profundidades de 0-5, 5-10, 10-20, 20-40, 40-60, 60-80, 80-100, 100-160 e 160-200 cm. Utilizaram-se os métodos densimétrico e granulométrico para o fracionamento da matéria orgânica do solo, obtendo-se: FLL (fração leve livre), FLI (fração leve intra-agregada), F-areia (fração areia), F-argila (fração argila) e F-silte (fração silte). Na superfície, 60 % do C do solo estão contidos na camada de 0-5 cm, associados à FLL. A F-argila foi responsável por 70 % do C retido entre 0 e 200 cm de profundidade. Ocorreu ganho de C de 12,7 g kg-1 na FLL, comparando-se FP e SS; e de 4,4 g kg-1 relacionando FP e SAF, demonstrando que áreas de SS e SAF recuperam o C orgânico do solo, sendo alternativas viáveis de recuperação de solo submetidos à degradação e aos cultivos intensos na Amazônia. Os maiores estoques totais de C nas frações do solo foram: (101,3 Mg ha-1 de C - SAF) > (98,4 Mg ha-1 de C - FP) > (92,9 Mg ha-1 de C - SS) > (64,0 Mg ha-1 de C - P). As formas de uso da terra na Amazônia influenciam a distribuição do C nas frações do solo, ocasionando modificações em curto ou longo prazo.

Organic matter plays an important role in many soil properties, and for that reason it is necessary to identify management systems which maintain or increase its concentrations. The aim of the present study was to determine the quality and quantity of organic C in different compartments of the soil fraction in different Amazonian ecosystems. The soil organic matter (FSOM) was fractionated and soil C stocks were estimated in primary forest (PF), pasture (P), secondary succession (SS) and an agroforestry system (AFS). Samples were collected at the depths 0-5, 5-10, 10-20, 20-40, 40-60, 60-80, 80-100, 100-160, and 160-200 cm. Densimetric and particle size analysis methods were used for FSOM, obtaining the following fractions: FLF (free light fraction), IALF (intra-aggregate light fraction), F-sand (sand fraction), F-clay (clay fraction) and F-silt (silt fraction). The 0-5 cm layer contains 60 % of soil C, which is associated with the FLF. The F-clay was responsible for 70 % of C retained in the 0-200 cm depth. There was a 12.7 g kg-1 C gain in the FLF from PF to SS, and a 4.4 g kg-1 C gain from PF to AFS, showing that SS and AFS areas recover soil organic C, constituting feasible C-recovery alternatives for degraded and intensively farmed soils in Amazonia. The greatest total stocks of carbon in soil fractions were, in decreasing order: (101.3 Mg ha-1 of C - AFS) > (98.4 Mg ha-1 of C - FP) > (92.9 Mg ha-1 of C - SS) > (64.0 Mg ha-1 of C - P). The forms of land use in the Amazon influence C distribution in soil fractions, resulting in short- or long-term changes.

As várzeas do rio Solimões são áreas inundáveis com predomínio de Gleissolos, onde se estabeleceu grande parte da população rural do Estado do Amazonas. Os objetivos deste trabalho foram caracterizar e classificar cinco perfis de Gleissolos, distribuídos em três áreas da bacia do Médio Amazonas, localizados nas várzeas dos municípios de Manacapuru e Iranduba. Após a descrição morfológica dos solos, coletaram-se amostras dos seus horizontes para caracterização física, química e mineralógica. Similarmente, todos os perfis apresentaram expressiva gleização na matriz do solo, com cores cinzenta a cinzenta-esverdeada, nos horizontes mais superficiais, e cinzenta-clara a cinzenta-escura, nos subsuperficiais, denotando a redução do ferro. Os teores mais elevados da fração areia em horizontes de subsuperfície indicaram presença de diferentes camadas de deposição fluvial, enquanto os elevados teores de silte evidenciaram a natureza sedimentar recente e o baixo grau de desenvolvimento pedogenético desses solos. Os cátions predominantes nos solos foram Ca2+ e Mg2+, que apresentaram porcentagens de sódio trocável (PST), com amplitude de variação entre 0,70 e 2,09. Os valores de carbono orgânico encontrados foram menores de 80 g kg-1, apresentando a natureza mineral dos sedimentos recém-depositados. A composição mineralógica da fração argila revelou presença significativa de argilominerais 2:1, mas sem grande variabilidade entre os perfis. Esses resultados refletiram-se em elevada soma e saturação por bases, caracterizando solos eutróficos e com argila de atividade alta.

The floodplains of the Solimões River are areas periodically flooded with predominance of Gleisols,where have lived a large number of small farmers of the region. The purpose of this study was to characterize and classify five profiles of Gleysoils distributed in three floodplain areas of the Middle Amazon basin, located in the municipalities of Manacapuru and Iranduba. After the morphological description, the soil horizons were sampled to perform physical, chemical and mineralogical analyses. Similarly, significant gleization was observed in all profiles of the soil matrix, with gray to gray-green color in the surface, and light to dark gray in the subsurface horizons, denoting iron reduction. The highest levels of the sand fraction in the subsurface horizons indicated the presence of different layers of fluvial deposition, while the high silt contents evidenced the nature of recent sediments and the low degree of pedogenetic development of these soils. The predominant soil cations were Ca2+and Mg2+, with a percentage of exchangeable sodium (ESP), varying from 0.70 to 2.09. The organic carbon contents were lower than 80 g kg-1, indicating recently deposited mineral sediments. The mineralogical composition of the clay fraction showed a significant presence of 2:1 clay minerals, but little variability among profiles. These results are reflected in high sum of bases and base saturation, characterizing eutrophic soils with high clay activity.

O cultivo protegido de oleráceas é uma atividade em expansão no Amazonas. Várias são as vantagens em comparação ao cultivo sob condições de campo: colheita durante o ano todo, precocidade, aumento de produtividade e melhoria da qualidade dos produtos. O objetivo deste trabalho foi caracterizar o modelo de cultivo protegido utilizado em Iranduba, região de Manaus, com ênfase na produção de pimentão. Com base nas respostas obtidas em um questionário aplicado a nove produtores da região, verificou-se que 67% dos produtores entrevistados nunca tinham produzido hortaliças anteriormente e que a maioria utiliza casa-de-vegetação do tipo capela convectiva, com tamanho variando entre 160 e 495 m², a um custo de R$ 7,30 a 10,0 por m². A área média cultivada foi de 0,68 ha por produtor. O pimentão é a hortaliça predominante nas casas-de-vegetação. Para o seu cultivo, apenas 22% dos entrevistados realizaram análise de solo e calagem. Ainda assim, as quantidades de calcário e adubos utilizadas não são baseadas na análise. O solo é preparado mecanicamente por 89% dos entrevistados e todos utilizam gotejamento e fertirrigação. A água é proveniente de poços artesianos, mas não é feita análise da sua adequação à atividade. Pragas e doenças são controladas utilizando os agrotóxicos disponíveis no mercado, não raro nas mesmas dosagens e aplicações recomendadas para o cultivo convencional. A produtividade de pimentão no primeiro plantio atinge 125 t ha-1, com queda brusca, de até 40%, a partir do segundo plantio. Enquanto metade dos produtores entrega a produção a atravessadores, a outra metade comercializa em feiras e supermercados. Apesar de enfrentarem diversos desafios (assistência técnica deficiente, alto custo e baixa durabilidade das estruturas, falta de cultivares adaptadas ao clima local, indefinição de práticas de condução das lavouras), 67% dos produtores entrevistados gostariam de ampliar a área com cultivo protegido.

The protected cultivation of vegetables is an activity in expansion in Amazonas State, Brazil. There are several advantages in comparison to the cultivation under field conditions: harvest all year long, precocity, increase of productivity and improvement of the quality of the product. The aim of this work was to characterize the use of protected cultivation model in Iranduba, region of Manaus, with emphasis on sweet pepper production. On the basis of the answers gotten in an questionnaire applied to the nine producers of the region, 67% of the producers interviewed had never produced vegetables previously and that most of them used the convective chapel greenhouse type, with size varying between 160 and 495 m², at a cost of R$ 7,30 to 10,0 on each m². The cultivated average area was of 0,68 ha for producer. The sweet pepper is the predominant vegetable in the greenhouse. For its culture, only 22% of the interviewed ones had carried through soil analyses and soil liming. Even so, the used amounts of lime and fertilizer were not based on soil analyses. The soil is prepared by tractor by 89% of the interviewed ones and all use dripping and fertirrigation. The water comes from artesian wells, but analyses of its adequacy for the activity are not made. Plagues and illnesses are controlled using the available agricultural defensive in the market, usually in the same dosages and applications recommended for the conventional cultivation. The sweet pepper productivity in the first planting reaches 125 t ha-1, with a sudden fall, of up to 40%, from the second planting on. While half of the producers deliver the production to midlemen, the other half is commercialized in fairs and supermarkets. Although the diverse challenges (deficient technical assistance, high cost and low durability of the structures, lack of suitable cultivars for the local climate, definition lack of management of the culture), 67% of the interviewed producers would like to extend the area under protected environment.