Resumo

HERNANDEZ-HERNANDEZ, Rosa M.; RAMIREZ, Elizabeth; CASTRO, Ignacio  e  CANO, Sandra. Changes in quality indicators of hillside soils reforested with pines (Pinus caribaea) and eucalyptus (Eucalyptus robusta). Agrociencia [online]. 2008, vol.42, n.3, pp.253-266. ISSN 2521-9766.

Maintaining soil quality is critical for environmental sustainability, an especially important aspect for tropical hillside soils. Several fractions of soil organic matter (OM) have been recognized as good indicators of soil quality and resilience. Therefore, organic carbon, light and heavy soil fractions, microbial biomass, basal respiration, humic and fulvic acids as well as aggregate stability were evaluated in hillside soils which surround the Reservoir La Mariposa, which supplies drinking water to the city of Caracas, Venezuela, where the vegetation has changed due to population increase. Using randomized stratified sampling, three soil samples (0-10 cm; each with 10 subsamples) were taken from three 20 x 30 m plots (experimental units), from four adjacent soils pertaining to humid forests (BH), secondary savannas (SS) and pine (Pin) and eucalyptus (Eu) (treatments) plantations. The objective was to determine the effect of reforestation on quality indicators using pines and eucalyptus in hillside soils. Using analysis of variance (one way) and Tukey test (p<0.05), a significant decrease in C (more than 55%) was found in Pin and Eu soils compared with that of BH. Other OM fractions: microbial biomass (BH:124.0 vs Pin:73.7 vs Eu:113.7 kg ha^-1), light fraction C (BH:3.9 vs Pin:1.2 vs Eu:2.3 Mg ha^-1), humic acid/fulvic acid relation (BH:5.0 vs Pin:2.3 vs Eu:3.7) showed similar behavior. Secondary savanna soils presented intermediate values for the organic fractions and higher values for aggregate stability. Considering the environmental fragility and the significant changes in the indicators evaluated, it appears adequate to allow the natural succession process to occur instead of continuing current reforestation practices for management of the zone.

Palavras-chave : Aggregates; microbial biomass; carbon; eucalyptus; pines.

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