Neste trabalho foram avaliados fatores relacionados com a suscetibilidade a erosão em entressulcos de um Neossolo Litólico submetido a diferentes intensidades de uso e manejo do solo. O experimento foi realizado em condições de laboratório, utilizando-se amostras deformadas de solo colocadas em parcelas experimentais (0,23 m2) e declividade de 0,09 m m-1. O delineamento experimental utilizado foi em blocos casualizados, em que foram aplicadas chuvas simuladas com intensidade de 100 mm h-1 para os seguintes tratamentos: (I) solo cultivado com fumo sob preparo convencional (PC); (II) solo cultivado com fumo sob plantio direto (PD) e (III) solo sob mata nativa (MN). Para avaliar a suscetibilidade a erosão em entressulcos utilizaram-se índices referentes à relação energia cinética total (chuva e escoamento) sobre perda de solo, taxa média de desagregação e índice de estabilidade de agregados, cujos resultados mostraram que os fatores relacionados com a suscetibilidade a erosão em entressulcos estão associados não apenas com características e propriedades que conferem coesividade ao solo, mas, também, com condicionantes que afetam a hidráulica do escoamento e, consequentemente, a fase de transporte dos sedimentos.

The processes of occupation and exploitation in the Amazon have been increasing, and as a consequence, forest areas are being replaced by agroecosystems. As a consequence of this change, changes have been occurring in the soil attributes, and consequently, in the stability of aggregates in these environments. Thus, this work had two objectives: the first was to evaluate the impacts generated by the conversion of forests into agroecosystems on the soil attributes that are related to aggregates, in the southwestern region of the Amazon; the second objective was to evaluate the roles of pedophysical and pedochemical parameters on the stability of soil aggregates. The study was carried out on rural properties located in the southern part of Amazonas State, Brazil. Eight areas under different agroecosystems were selected: in the municipality of Canutama: (i) annatto, (ii) guarana, and (iii) cupuassu; in the municipality of Humaitá: (iv) cassava, (v) agroforestry, and (vi) sugarcane; and in the municipality of Manicoré: (vii) pasture and (viii) native forest. Unformed soil samples were collected from the 0.00–0.10 m layer and analyzed for aggregate stability, bulk density, soil organic carbon, and soil organic carbon stock. Univariate, bivariate, and multivariate analyses were performed. The largest soil aggregations occurred in the annatto, guarana, sugarcane, and pasture agroecosystems. We associate the greater aggregation capacity of soils with factors that are inherent to the cultivated species and soil properties. The first factor corresponds to the adaptability of the Amazonian and grass species and their ability to produce biomass. The second factor is related to the physical and chemical properties of Amazonian soils, largely influenced by the sand fraction, soil organic carbon, soil acidity, and availability of exchangeable Ca and Mg.

Light soils are more susceptible to degradation and need to be exploited in a conservational manner, thus avoiding rapid degradation. The objective of this study was to evaluate the physical-hydraulic properties of an Ultisol under no-tillage and crop-livestock integration in the Cerrado of eastern Maranhão state, Brazil. The evaluated managements were one area under no-tillage system for fourteen years (soybean/ millet) and three areas with different histories of adoption of the crop-livestock integration (CLI) system under no-tillage (soybean/millet), with the difference being: times of entry with CLI (2, 4 and 8 years), as well as a native Cerrado area, considered a control. Soil collection was carried out in June 2018 at depths of 0.00-0.10, 0.10-0.20, 0.20-0.30 and 0.30-0.50 m. Disturbed and undisturbed samples were collected to determine the following variables: bulk density, porosity, resistance to penetration, retention curve and available water capacity. Data were subjected to the calculation of means and confidence intervals (95%). The area with a recent history of crop-livestock integration showed better density, porosity, resistance to penetration, water storage capacity and available water. No-tillage for fourteen years leads to high resistance to penetration, less porosity and low water storage capacity. The integrated system (CLI) improves the quality of the physical- hydraulic properties and the values found are similar to those observed in an area under native vegetation.

The Seridó Desertification Region is a result of inadequate management of the native Caatinga vegetation, which generated degraded areas with little or no capacity for plant production. The area has experienced a succession of different land uses, but little is known about the impact of these changes. The present study tested the hypothesis that the intense degradation of the Caatinga drastically decreased vegetal biomass production, which favored direct soil exposure and resulted in a lower abundance and diversity of species and groups of vegetation as well as microorganisms. This study aimed to quantify some of the main physical, chemical, and microbiological properties of Alfisol ( Luvissolo Crômico órtico lítico ) and Entisol ( Neossolo Litólico eutrófico típico ) under different plant covers in the Seridó Desertification Region, in the municipality of Parelhas, in the state of Rio Grande do Norte (RN), Brazil. Three different areas were studied: an area of preserved Caatinga, a recovery area with jurema [ Mimosa tenuiflora (Willd.) Poir.], and a degraded area. Soil samples were collected from the 0.00-0.10 m soil layer and later characterized in terms of their physical and chemical properties. The microbiological characteristics analyzed were microbial activity (microbial biomass carbon and microbial respiration) and glomalin. The soil under the Caatinga vegetation exhibited better properties than the other analyzed soils. Aggregate stability was the physical property with the highest potential for differentiating between areas. Glomalin, which is associated with the presence of mycorrhizae, and which, in turn, is related to the uptake of P, which is often deficient in these soils, was the most discriminating microbiological variable according to an analysis of canonical variables. The total of Ca²⁺ and Mg²⁺ was the most discriminating chemical properties, and played a positive role in soil aggregation, especially Ca²⁺.

Solos arenosos representam um desafio para a produção agrícola. Assim, o objetivo deste estudo foi caracterizar o comportamento físico-hídrico de três classes de solos arenosos através da curva de retenção de água, índice S e distribuição de poros por tamanho no geombiente dos Tabuleiros Costeiros de Arez, no estado do Rio Grande do Norte. Amostras de solo com estrutura indeformada foram coletadas nos horizontes superficiais e subsuperficiais de três perfis de solos para caracterização físico-hídrica através dos seguintes atributos: Curva de retenção de água no solo, capacidade de água disponível às plantas, potencial matricial no ponto de inflexão, umidade no ponto de inflexão, água prontamente disponível, índice de vazios, capacidade de campo relativa (CCr), distribuição de poros por tamanho, carbono orgânico total e textura do solo. Tanto em superfície quanto em subsuperfície o teor de água disponível nos solos foi influenciado positivamente pelo conteúdo de carbono orgânico e, em subsuperfície pelo aumento do teor de argila e pelo percentual de areia fina. A distribuição de poros por tamanho se apresentou de forma regular, característica de solos arenosos, com predomínio de macroporos e mesoporos, exceto para os horizontes subsuperficiais do solo no terço inferior com caráter fragipânico, onde predominou micro e criptoporos. O índice S reduziu em profundidade e os valores de CCr ficaram abaixo de 0,6, indicando uma baixa capacidade de retenção de água no solo, independentemente da posição deles na paisagem. Embora, os solos no terço inferior tenham apresentado maiores teores de água disponível.