In agricultural fields soil compaction is a major cause of physical degradation. Degree of compactness (DC) is a useful parameter for characterizing compaction and the response of crops for different soils. The objectives of this study were: (1) to identify the critical DC and PR values for soybean [Glycine max (L.) Merrill] using plant growth variables and (2) to verify the relationship between DC and PR, and assess which parameter is recommended for the evaluation of soil compaction. The study was conducted in a greenhouse in a completely randomized factorial design of 4 textures × 5 compaction levels for sandy loam and sandy clay loam soils, and 3 compaction levels for the clayey and very clayey soils. Soil samples were collected from the surface of a Xantic Kandiudox from the NE region of the State of Pará, Brazil. The DC was calculated from the maximum bulk density obtained by the Proctor test, and the PR curve was determined in undisturbed samples equilibrated in different matric potentials. The growth and development of the soybean was favored in the DC range of 80 to 85%, regardless of soil texture. The critical degree of compactness for the growth of soybean was around 98% regardless of soil texture, while the critical values for penetration resistance at field capacity varied according to soil texture and bulk density and were 28.2, 5.6, 3.5, and 5.2 MPa for the sandy loam, sand clay loam, clayey and very clayey soils, respectively. The root length was the plant growth variable most susceptible to soil compaction. Change in soil penetration resistance was poorly related with change in degree of compactness showing that one parameter cannot be replaced by the other. Because PR is quickly determined in field and have a direct relationship with plant growth, for the soils evaluated in this study we recommend the use of soil PR to assess the state of soil compaction.

No abstract

The açaí palm (Euterpe oleracea Mart) is native to the floodplains of central and South America and is cultivated in Brazil for its berries, which are considered to be a 'superfood'. The waste açaí fiber and seeds obtained after fruit processing pose a challenge since they remain unutilised despite being an abundant waste by-product of açaí processing.This leads to a build-up of waste, regular dumping and environmental management challenges. Here we examine the potential use of açaí seed biochar as a soil conditioner. The biochar was produced from waste seeds in a handmade kiln, incorporated into two soils of different textures and then compacted in volumetric rings with a hydraulic press. The samples were kept in a greenhouse for a 270-day incubation period. After this, the samples were evaluated for their soil physical and chemical attributes. Nine months after the application of the açaí seed biochar, soil physical properties were not affected, except for the soil aggregate size distribution, for which the highest dosage resulted in a larger weighted average diameter. However, biochar increased phosphorus, potassium and magnesium contents, and reduced the aluminum content, which was reflected in an increase of the base saturation and a reduction in aluminum saturation. Therefore, within a relatively short time period, the biochar was found to improve soil chemical quality more so than soil physical properties, thus offering potential as a sustainable solution to manage açaí waste in the Amazon region.

In areas cultivated with oil palm, typically mechanized field operations using heavy vehicles may negatively affect soil physical properties and productivity. The aim of this study was to evaluate soil physical quality in an area cultivated with oil palm by monitoring the temporal variation of the soil water content and relating it to the critical limits of the least limiting water range. Soil bulk density (Bd), soil penetration resistance (SR), least limiting water range (LLWR), and water stress days (WSD) were used to assess soil physical quality in planting rows (PR) and the traffic zone (TZ) at depths 0-20, 20-40, and 40-60 cm. The Bd was higher and the LLWR was reduced in TZ only at the surface layer. The effect of temporal variation in soil water content on the soil physical quality was higher in TZ, mainly in subsurface layers. Bd and LLWR did not affect the fresh fruit bunch production; however, WSD in TZ at 20-40 and 40-60 cm layers provided evidence of effects of temporal variation of soil water content on oil palm productivity.

A análise granulométrica do solo é uma ferramenta básica no processo de caracterização do solo tanto para fi ns taxonômicos quanto para o entendimento do comportamento e manejo do solo. O objetivo foi avaliar a efi ciência do hidróxido de sódio (NaOH) e hexametafosfato de sódio (HMP), como dispersantes químicos na análise granulométrica pelo método da pipeta, bem como testar a efi ciência do método do densímetro sugerido pela Embrapa, em Latossolos de diferentes classes texturais do Estado do Pará. Foram utilizadas amostras de Latossolos Amarelos coletadas na camada de 0-20 cm de profundidade em quatro localidades distintas situadas no Pará, buscando compor a ampla variação textural representativa dos solos da região. O delineamento experimental utilizado foi inteiramente casualizado com quatro solos, três métodos de análise granulométrica e três repetições, totalizando 36 unidades experimentais. O NaOH foi mais efi ciente na dispersão das partículas do solo que o HMP. Utilizando o NaOH como dispersante químico, o método do densímetro foi tão preciso quanto o método da pipeta, sendo, portanto, o mais indicado para atender à constante demanda por análise textural nos laboratórios da região, devido à rapidez e praticidade na sua determinação.

The aim of this study was to evaluate the critical soil bulk density from the soil penetration resistance measurements for soybean root growth in Brazilian Amazon Oxisols. The experiment was carried out in a greenhouse using disturbed soil samples collected from the northwest of Para characterized by different texture. The treatments consisted of a range of soil bulk densities for each soil textural class. Three pots were used for soybean growth of and two for the soil penetration resistance curve. From the fitted model, the critical soil bulk density was determined considering the penetration resistance values of 2 and 3 MPa. After sixty days, plants were cut and root length, dry mass of root, and dry mass of shoots were determined. At higher bulk densities, the increase in soil water content decreased the penetration resistance, allowing unrestricted growth of soybean roots. Regardless of soil texture, the penetration resistance of 2 and 3 MPa had a slight effect on root growth in soil moisture at field capacity and a reduction of 50% in the soybean root growth was achieved at critical soil bulk density of 1.82, 1.75, 1.51, and 1.45 Mg m-3 for the sandy loam, sandy clay loam, clayey, and very clayey soil.

RESUMO: Embora a palma de óleo seja cultivada em grande escala e em diferentes tipos de solos no estado do Pará, mudanças nas propriedades físicas do solo nestas áreas não vêm sendo monitoradas. Assim, o objetivo do trabalho foi avaliar a qualidade física de um Latossolo Amarelo cultivado com palma de óleo após 30 anos de implantação. Amostras de solo com estrutura deformada e indeformada foram coletadas nas profundidades de 0-20 e 20-40 cm, na zona de tráfego. O grau de compactação (GC) foi calculado a partir da densidade máxima do solo obtida pelo teste de Proctor e sua resistência à penetração (RP) determinada em amostras equilibradas em dez potenciais matriciais. Influência das mudanças temporais da umidade do solo na RP também foram avaliadas. Os parâmetros GC e RP demonstraram que a área avaliada apresenta compactação. O GC nas duas profundidades ficou acima de 90% sendo mais intenso na camada de 0-20 cm. Porém, quando avaliado pela RP, o estado de compactação foi mais evidente na camada de 20-40 cm e, as variações na umidade do solo ao longo de um ano mostraram que nos meses mais secos o solo apresenta valores limitantes de RP nesta camada. Desta forma, este estudo indica que o crescimento e desenvolvimento da palma de óleo pode estar sendo restringido pela compactação e sobretudo pela elevada resistência à penetração nos meses de menor disponibilidade de água. ABSTRACT:Although oil palm is cultivated on a large scale and in different soil types in the state of Pará, changes in the soil's physical properties in these areas have not been evaluated. Thus, the objective of this study was to evaluate the physical quality of a Yellow Latosol cultivated with oil palm, 30 years after implantation. Soil samples with disturbed and undisturbed structure were collected at 0-20 and 20-40 cm depths, in the machinery traffic zone. The degree of compaction (DC) was calculated from the maximum soil bulk density obtained by the Proctor test, and soil penetration resistance (PR) was determined in soil samples equilibrated in ten matric potentials. Temporal changes in soil moisture in PR were also evaluated. Both parameters showed that the evaluated area has an indication of compaction. The DC in both depths was above 90% and was more severe in the 0-20 cm layer. However, when evaluated by PR, the compaction was more evident in the 20-40 cm layer, and variations in soil moisture over a year showed that in the drier months, the soil showed high values of PR in this layer. Thus, this study indicates that the growth and development of oil palm may be restricted by the soil's compaction and mainly by the high penetration resistance in the months of reduced water availability.

Direitos para esta edição cedidos à Atena Editora pelos autores. Open access publication by Atena Editora Todo o conteúdo deste livro está licenciado sob uma Licença de Atribuição Creative Commons. Atribuição-Não-Comercial-NãoDerivativos 4.0 Internacional (CC BY-NC-ND 4.0).O conteúdo dos artigos e seus dados em sua forma, correção e confiabilidade são de responsabilidade exclusiva dos autores, inclusive não representam necessariamente a posição oficial da Atena Editora. Permitido o download da obra e o compartilhamento desde que sejam atribuídos créditos aos autores, mas sem a possibilidade de alterá-la de nenhuma forma ou utilizá-la para fins comerciais. Todos os manuscritos foram previamente submetidos à avaliação cega pelos pares, membros do Conselho Editorial desta Editora, tendo sido aprovados para a publicação com base em critérios de neutralidade e imparcialidade acadêmica.A Atena Editora é comprometida em garantir a integridade editorial em todas as etapas do processo de publicação, evitando plágio, dados ou resultados fraudulentos e impedindo que interesses financeiros comprometam os padrões éticos da publicação. Situações suspeitas de má conduta científica serão investigadas sob o mais alto padrão de rigor acadêmico e ético.