Finally, no interaction was detected between species and planting spacing factors, therefore, the species identified had a better performance regardless of the planting spacing used. ha-1) maximized the production of basal area and the volume for the species evaluated.as promising for commercial reforestation programs in areas with a water deficit in the tropical dry forest. and the Colombian provenance of Eucalyptus pellita F. The study identified the Brazilian provenances of Eucalyptus camaldulensis Dehnh, Eucalyptus urophylla S.T. Survival and growth were evaluated at twenty-four months of age. The planting spacing factor (three planting spacings) was assigned to the main plots and the species factor (nine eucalypt species) was assigned to the subplots. A split-plot arrangement with two replicates was used as the experimental design. The aim of this study was to evaluate the performance of nine eucalypt species planted with three different spacings under the environmental conditions of the tropical dry forest of the inter-Andean valleys of Colombia. The establishment of new forest plantations requires making important decisions starting with the selection of the species to be planted, as well as the choice of an adequate planting spacing to guarantee the maximization of wood production. The change imposed by the progressive increase in the Eucalyptus cultivation time positively influenced the activity and C transformation of SMB. Only the metabolic quotient among the microbiological indices was sensitive to the Eucalyptus cultivation time, with a significant reduction in rotation 3 (131.0 mg g⁻¹ day) compared to rotations 1 and 2 (average of 269.1 mg g⁻¹ day). Following a similar pattern, the microbial biomass carbon (MB-C) levels showed increases of 52 and 47% in rotation 3 in relation to rotation 1 and 2, respectively. This was reflected in increases in C immobilization in microbial biomass (MB-C) and in the efficiency of converting organic carbon to MB-C and reducing soil carbon losses. The increase in Eucalyptus cultivation time caused increases in litter accumulation and soil organic carbon, which represented an increase of 50% in rotation 1 compared to rotations 2 and 3. The carbon and nitrogen contents of the soil microbial biomass were determined by the fumigation-extraction method and the soil microbial activity was based on the amount of CO2 evolved. ![]() ![]() Soil collections were performed at a depth of 0–10 cm. The study was carried out in commercial plantations of Eucalyptus urophylla in the first, second and third rotations (area cultivated 4, 9 and 15 years ago, respectively) using a fragment of native forest as a reference. Therefore, the aim of this study was to evaluate changes in the biomass and microbial activity of tropical soil submitted to successive Eucalyptus cultivation rotations. Although there are several studies on SMB in Eucalyptus plantations in Brazil, there are still no records of investigations which have evaluated the effect of successive crop rotations on soil microbial biomass. Soil microbial biomass (SMB) is considered an important indicator of changes in the soil organic carbon dynamics.
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