Soil organic carbon and soil microbial biomass in Acacia mangium plantation in the Savanna of Roraima

The aim of this study was to evaluate the effects of Acacia mangium plantation in the Roraima's Savanna, on soil organic carbon and soil microbial biomass. Soil samplings were collected on the depths of 0-20 cm and 20-40 cm in two Acacia mangium plantation sites, about five years old, and in two sites of native savanna as reference. One of the A. mangium sites (located at Fazenda Cigolina) was composed by a homogeneous plantation (3.6 m between row and 2.0 m between trees) and, the other one (located at Campo Experimental Agua Boa Experimental - CEAB) was composed by a plantation on which the planting distances had strips of two rows 6 meters apart, 2.5 meters between trees and 30 meters between strips). Soil samples were analyzed regarding soil organic carbon, microbial biomass carbon, soil basal respiration and metabolic quotient, besides soil fertility attributes. Results showed that A. mangium plantations did not provide significant increases of organic carbon on the soil comparing with sites used as reference. However, generally, A. mangium plantation increased soil microbial biomass carbon and reduced metabolic quotient, indicating a possibility of soil organic carbon accumulation in long-term. It was also observed that, soil biomass microbial carbon was higher, followed by smaller metabolic quotient at CEAB A. mangium plantation compared with Cigolina and reference sites, showing that planting design exercised influence on soil microbial biomass.

Soil basal respiration; metabolic quotient; Amazonian; forest plantation; soil quality

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