Effects of Enzyme Activity of Soil in Area Submitted to Pasture in the Roraima State, Amazonia, Brazil.

EFFECTS OF ENZYME ACTIVITY OF SOIL IN AREA SUBMITTED TO PASTURE IN THE RORAIMA STATE, AMAZÔNIA, BRAZIL

Soil enzyme activities can provide information how soil management affects soil potential to perform processes, such as decomposition, and nutrient cycling. Were investigated the enzyme activities of soil (urease, phosphomonoesterase, ß-glucosidase and dehydrogenase) of Xhantic Hapludox submitted to pasture with two types of Brachiaria for ten years and  the  native forest  area, in two depths ( 0 – 10 and 10 – 20 cm) at Roraima State, Amazônia, Brazil. Twelve areas were selected for study of enzymatic activity. Four areas in conditions of native forest, four areas converted to pasture with Brachiaria decumbense and four converted to pasture with Brachiaria humidicola. The areas converted to pasture were deforested with chainsaw for tree felling. In the first year, the wood and stumps were removed by tractor, and after this the areas were burned for the total cleaning. The soil sampling was performed during the dry season (February and March 2012). In each area was delimited 0.5 hectares and represented by 10 single samples collected at 0-10 and 10-20 cm. The samples were transported to the laboratory, where they were air dried, passed through a 4 mm sieve and sent to the Laboratory of the University of Santiago de Compostela, Spain. The activity of enzymes (urease, dehydrogenase, phosphomonoesterase, and β-glucosidase) was measured in the soils. The enzyme activity range from 1.2 to 6.6 μmol NH₃ g^-1h^-1 (urease), 1.1 to 2.8 μmol PNP g^-1 h^-1 (phosphomoesterase), from 0.08 to 0.31 μmol PNP g^-1 h^-1 (β-glucosidase) and 0.05 to 0.20 μmol INTF g^-1 h^-1 (Dehydrogenase). The activity of enzymes was significantly reduced in areas managed with Brachiaria and was higher in the layer 0-10 cm. Among the managed areas, the enzyme activity was slightly higher in area with B. decumbense. These results may be explained by the lower of organic matter in managed areas.