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The cultivation of Hevea brasiliensis (rubber) is promoted as a productive and ecological alternative, especially in agroforestry systems, although research is still required to address its impact on soil chemical conditions. This study aimed evaluate the possible effects of five types of land use on the chemical properties of horizons A and B in soils of the Colombian Amazon: agroforestry system of H. brasiliensis with timber and fruit trees, agroforestry system of H. brasiliensis associated with stubble, H. brasiliensis monoculture, secondary forest as positive control and native grass as negative control. The conditions of pH, exchangeable aluminum, organic carbon, potassium, phosphorus, calcium, magnesium, base saturation and cationic exchange capacity were evaluated. Similarities in soil chemical properties were found between secondary forest, agroforestry systems with fruit trees and agroforestry systems associated with stubble. The H. brasiliensis monoculture did not present significant differences with the native pasture. The pH was the only variable affected by soil use, while the percentage of organic carbon and the contents of phosphorus, calcium, magnesium and potassium changed depending on the A and B horizons, demonstrating that the variability of the chemical fertility of the clay soils of the Amazon are more related to the characteristics of their horizons than to the type of land use. [ABSTRACT FROM AUTHOR]

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This study aimed to evaluate the early growth of three rubber tree clones (Hevea brasiliensis) (FX 4098, FDR 5788, and control IAN 873) in four planting systems with cupuasu (Theobroma grandiflorum) and banana trees (Musa AAB) at two localities in Caquetá (Colombian Amazonia). A completely randomized block design with three replications and split-plot arrangement, analyzed with a general linear mixed model, was used at each locality. Total height (AT), trunk circumference (CT), canopy area (AC) and leaf area index (IAF) were evaluated one and two years after establishment of rubber trees. Trunk circumference was the variable most correlated with different growth indices (r ≥ 0.94). Four growth indices were strongly influenced by temporal and clonal variation and by planting system (p < 0.01). The only significant differences between the two localities were for AC (p < 0.05). System x clone interaction was significant for IAF (p < 0.01). After two years, the highest growth indices were observed in rubber tree clone FX 4098 (AT = 4.43 m; CT = 13.00 cm, AC = 4.62 m2; LAI = 1.37), and in two of the three agroforestry systems (AT ≥ 4.08 m, CT ≥ 11.43 cm, AC ≥ 4.01 m2; IAF ≥ 1.54) compared with the control system (monoculture). [ABSTRACT FROM AUTHOR]