ABSTRACT Amazonian soils have been suffering severe changes resulting from human activities in the region, causing significant changes in soil attributes that can contribute to greater susceptibility to erosion processes. Therefore, the present work aimed to estimate the erodibility in natural and anthropic environments in the southern region of the Amazon. Eight areas in the region were selected, including areas of native forest, savannah, cerradão, pasture and reforestation, delimiting 32 sampling points per area, with collections at a depth of 0.00-0.20 m, totaling 256 samples. Next, texture analysis and quantification of soil organic carbon were performed, and then erodibility was estimated by indirect prediction methods, Tukey’s test, Pearson’s correlation and factorial analysis of principal components. According to the results obtained, it was observed that the evaluated areas of native forest 1 and 2, cerradão and pasture present high susceptibility to erosion in relation to the cerrado, reforestation with genipap, teak and mixed areas. Therefore, it was noted that the high level of erodibility is associated with a greater predominance of sand fraction, K factor, Ki Kr and low clay content, as well as with the management employed in the areas.

Abstract The diversity of forest species is an intrinsic characteristic of the Amazon biome, with litter being the main responsible for the largest portion of nutrients returned to the soil. Thus, the objective of this study was to quantify the annual production of burlap and to determine the rate of decomposition over one year, comparing the results in the different study environments. The study was developed in the municipality of Humaitá-AM. For the evaluation of the litter production, ten cone collectors were randomly installed in each study area. Each litter sample was placed separately in properly identified paper bags and taken to the laboratory and dried in a forced air circulation oven at 65 ° C. The litter decomposition rate was estimated by mass loss analysis using litter bags. Litter production with the highest annual average was 8,03 Mg ha-1 year -1 for the native forest environment, with no significant difference for the other study areas. Among the fractions of the litter that contributed the most to the leaf, reaching a higher average percentage in the year of 72,1% for the environment of reforestation with teak (Tectona grandis L.). The decomposition of litter occurred more rapidly (0.0025 g g-1 day) in the reforestation environment with genipap (Genipa americana L.), requiring 277,26 days to decompose half of the leaf material.

Resumo A diversidade de espécies florestais é uma característica intrínseca do bioma Amazônico, sendo a serapilheira a principal responsável pela maior parcela dos nutrientes devolvidos ao solo. Dessa forma, o objetivo deste estudo foi quantificar a produção anual de serapilheira e determinar a velocidade de decomposição ao longo de um ano, comparando os resultados nos diferentes ambientes de estudo. O estudo foi desenvolvido no município de Humaitá-AM. Para a avaliação da produção de serapilheira, foram instalados de modo aleatório dez coletores cônicos em área de Floresta Nativa, área de Reflorestamento com Teca (Tectona grandis L), área de Reflorestamento com Jenipapo (Genipa americana L.) e ambiente de Reflorestamento considerado Misto, composto pelas espécies Mogno (Swietenia macrophylla King.), Andiroba (Carapa guianensis Aubl.), Jenipapo (Genipa americana L.), Teca (Tectona grandis L.) e Sumauma (Ceiba pentandra). Cada amostra de serapilheira foi colocada, separadamente, em sacos de papel devidamente identificados e levadas para laboratório e secas em estufa de circulação de ar forçado a 65°C. A estimativa da taxa de decomposição da serapilheira foi feita pela análise de perda de massa utilizando-se litter bags. A produção de serapilheira média anual foi de 8,03 Mg ha-1 ano-1 para o ambiente de floresta nativa, e não houve diferença significativa para as demais áreas de estudo. Entre as frações da serapilheira, a que mais contribuiu foi a foliar, atingindo maior média percentual no ano de 72,1% para o ambiente de reflorestamento com teca (Tectona grandis L.). A decomposição da serapilheira ocorreu de forma mais acelerada (0,0025 g g-1dia) no ambiente de reflorestamento com jenipapo (Genipa americana L.), sendo necessários 277,26 dias para que fosse decomposta metade do material foliar.

RESUMO Os solos da região amazônica, apesar de estarem sob uma das florestas mais densas do mundo, são caracterizados, na sua maioria, pela baixa disponibilidade de nutrientes, sendo a serapilheira a principal via de entrada de nutrientes. O objetivo desse estudo foi quantificar a biomassa de raízes finas na época seca e chuvosa do ano, incluindo o carbono orgânico do solo, e comparar os resultados nos diferentes ambientes de estudo. O estudo foi desenvolvido em ambientes de floresta nativa e reflorestamento com idade acima de 20 anos, localizado no município de Humaitá- AM. Para avaliação da biomassa de raízes, foram realizadas coletas em dois períodos do ano: seco e chuvoso. Em cada uma das áreas de estudo foram escavadas manualmente cinco trincheiras, com dimensão de 0,40 m de profundidade por 0,40 m de largura, nas profundidades de 0-5, 5-15 e 15-30 cm. Para análise de carbono orgânico foram coletadas amostras de solo em forma de torrão nas mesmas profundidades. A produção de biomassa radicular no ambiente de floresta nativa ocorreu de forma mais intensa no período chuvoso, chegando a valores de 8,19 t. ha-1, superior a 3,57 t. ha-1 encontrado em reflorestamento. A densidade em função do volume de solo mostrou que a maior concentração se encontra nos primeiros 5 centímetros de profundidade, diferenciando significativamente nas camadas de 5-15 e 15-30 cm para área de floresta nativa. O carbono orgânico do solo apresentou significância entre o período seco e chuvoso para os ambientes de floresta natural e reflorestamento com jenipapo.

ABSTRACT The soils of the Amazon region, despite being under one of the densest forests in the world, are mostly characterized by the low availability of nutrients, with litter being the main route of nutrient entry. The objective of this study was to quantify the biomass of fine roots in the dry and rainy seasons of the year, including the organic carbon of the soil, and to compare the results in different study environments. The study was carried out in environments of native forest and reforestation aged over 20 years, located in the municipality of Humaitá – AM state. To assess the root biomass, collections were carried out in two periods of the year: dry and rainy seasons. In each of the study areas, five trenches, 0.40 m deep by 0.40 m wide, were dug manually at depths of 0-5, 5-15, and 15-30 cm. For the organic carbon analysis, soil samples were collected in the form of clods at the same depths. The production of root biomass in the native forest environment occurred more intensely in the rainy season, reaching values of 8.19 t. ha-1, greater than 3.57 t. ha-1 found in reforestation. The density as a function of the soil volume showed that the highest concentration is found in the first 5 centimeters of depth, differing significantly in the 5-15 and 15-30 cm layers for native forest area. The organic carbon of the soil showed significance between the dry and rainy seasons for the natural forest environments and reforestation with genipap.

ABSTRACT In the Amazon region, soil patches with an anthropic A horizon are found, called Indian black earths (IBEs). Indian black earths are highly fertile and, therefore, are deforested by small local farmers to cultivate without basic management that maintains soil and crop sustainability. Therefore, in order to evaluate the effect of using different cultures on the spatial variability of soil chemical attributes, three cultivated IBEs and one IBE under natural forest were selected for georeferencing and sample collection. The collection was made with a mesh system with 88 points per IBE, stratified in three layers: 0–0.05, 0.05–0.10 and 0.10–0.20 m. The soil was sampled, dried in the shade and sieved to obtain the fine earth fraction for analysis of chemical attributes. Descriptive statistical and geostatistical analyses were applied to the results. The use and management of soil influenced the spatial behavior of the chemical attributes of IBEs. The cultivation of Brachiaria over many years favored the reduction of the spatial variability of chemical attributes. The use of cacao and coffee crops also favored the homogeneity of the IBEs in relation to the natural forest, but not as much as for Brachiaria, likely due to the succession of crops that preceded these crops. The IBE in the forest contains a high natural spatial correlation in the first 0.1 m of the surface; however, more than 70% of this correlation is linked to a random variation.

ABSTRACT The objective of this work was to evaluate soil attributes and root distribution in areas under forest conversion to cultivated environments. The study was carried out in four areas: forest, cupuaçu, guarana and annatto, located in the municipality of Canutama, state of Amazonas. Soils and volumetric rings were collected in the layers 0.00 – 0.10; 0.10 – 0.20; 0.20 – 0.30; 0.30 – 0.40; and 0.40 – 0.50 m for analyses of physical and chemical attributes and root distribution. Univariate statistical analyses were carried out, the means were compared with the Tukey’s test (p < 0.05) and Pearson’s correlation (p < 0.05 and < 0.01). The forest area and the cultivated environments present soil chemical limitations for agricultural production, whereas the physical attributes presented satisfactory values. The chemical attributes underwent major changes and degradations upon conversion to agriculture. Major changes were observed in the layers of 0.00 – 0.10 and 0.10 – 0.20 m for the studied areas. Cupuaçu cultivation showed higher values of roots dry weight (RDW) and roots distribution (RD), with the highest values found in the 0.00 – 0.10 and 0.10 – 0.20 m layers.