Caracterização química, física, microbiológica e estabelecimento de indicadores e índices de qualidade de solos sob cacaueiros nativos na Amazônia

Abstract

Fruit native exploitation has a high potential for generating income linked to sustainable development and maintenance of ecosystem services. Cacao tree (Theobroma acao L.) is a fruit native to Amazon found under the dossal of trees in island regions. The native areas provide organic almonds for the production of fine chocolates. Objective of this study was to characterize and establish indicators and indexes of soil quality under native cacao trees, depending on the physical, chemical and microbiological properties of the soil. Deformed and undisturbed soil collections were carried out, depth 0-0.10 m, on Tatuoca Island (ST), Combu Island (SC) and Pacajá Community (SP), State of Pará. The soils were characterized in terms of chemical properties (pH, organic carbon, P, K, Ca, Mg, Al, potential acidity, total of bases, cation exchange capacity and base saturation) physical (texture, water content, microporosity, macroporosity, total porosity, textural, residual, structural and total void ratio textural and structural, bulk density, particle density and aggregate stability); microbiological, (basal respiration and carbon of microbial biomass, microbial density); biochemical (solubilization of P, production of siderophores, indole acetic acid - AIA, catalase, easily extractable glomalin content - FE-PRGS and total glomalin - T-PRGS); biological (root mass). High concentration of organic carbon contributed positively to results of total of bases, cation exchange capacity and base saturation in soils. Base saturation was >50% in soils. Tatuoca Island, Combu Island, Pacajá Community soils have textural class silty clay loam, silty loam and loam, respectively. Double exponential equation showed the bimodal behavior of pore distribution with the highest peak regarding the textural porosity in three soils. Minimum data set – CMD formed from principal component analysis – ACP selected the variables: pH in water, total of bases, total porosity, bulk density, carbon of microbial biomass and basal respiration as indicators of soil quality under native cacao trees. Soil quality indexes were high, next to 1, indicating the good quality of these soils. Density of microorganisms and biochemical characterization were realized in Tatuoca Island soil, where were a high number of colonies forming units bacterial (8.84x10+4). 13 bacterial isolates presented a halo characteristic of P solubilization in NBRIP medium, 4 produced siderophores, 3 produced AIA and 23 were positive for catalase. Glomalin was not the main link agent for aggregates, but there was a positive correlation between easily extractable glomaline and the aggregate mass with diameter < 2 mm. Total glomalin interacted positively with the phosphorus content. The root mass increased with the increase of the phosphorus content in Tatuoca Island soil. Soil quality indexes can be used for monitoring soil quality in a planted cocoa area and soils subject to hydromorphism and microorganisms from groups 1 and 2 of cluster analyses showed potential for promoting plant growth.