Impactos ambientais causados pelas queimadas nos solos do Distrito de Miranda no Município de Parambu - Ceará

Abstract

We evaluated the environmental impacts caused by the fires in soils of the District of Miranda in the Municipal district of Parambu, Ceará State through the analysis of the environmental physical-chemical parameters of the soils, the texture analysis, and the use of plots having collectors to store the soil transported by the rains and the determination of the soil erodibility factor (K). The soil samples were collected in the cultivation and native forest areas at depths of 0 - 20 cm and 20 - 40 cm, in the dry season. We compared the results of the analyses to the limits determined by EMBRAPA (1979). The pH parameter presents values among low acidity and average alkalinity and the organic matter content, with values between 0.6 and 1.3%, varied from low to average. The macronutrients (Nitrogen, Potassium, Calcium, Magnesium, Phosphorus and Sulfur), in spite of presenting values that differ from the sequence of EMBRAPA (1979), are present in the two areas. The exchangeable Aluminum presented a uniform concentration (0.00 cmolc/Kg), favoring the soil of the areas once its high content in the soil is highly harmful to most plants. The Cation Exchange Capacity – CEC, presented a larger concentration in the cultivation area (varying from 8 to 10 cmolc/Kg), showing that in that area, in which there were fires, because of its location there is the retention and fixation of a larger amount of exchangeable metallic cations in the soil, while in the native forest area the CEC value was low (varying from 3 to 4 cmolc/Kg). The degrees of base saturation, ranging from 89 to 100%, indicated a low leaching capacity. The Acidity potential, with values between 0.00 and 0.49 cmolc/Kg, indicates a low capacity of acidity in the soil. The values of the exchangeable sodium contents ranged from 0.06 to 0.41 cmolc/Kg, being classified as high. The electrical conductivity with values smaller than 4 dS/m, the exchangeable sodium percentage, with a value smaller than 15 and the pH value smaller than 15 classify the soil of the area in relation to those parameters as normal. The soil texture classification as sandy loam prevailed in the two areas and depths. The soils were classified according to EMBRAPA-CNPS (1999) in the Planossolo Hidromórfico ORDER, in the area of native forest ‘red’ and area of cultivation ‘red-yellow’ SUBORDER and Eutrófico BIG GROUP. The measures of soil loss were from 2 to 3 cm. The approximate K parameter value varied from 0.31 to 0.37 at the depth of 20 cm, what indicates high erodibility in the soil. The evaluation of the environmental impacts concerning the fires, through the macronutrients indexes, carried out in the cultivation and native forest areas, showed that that technique did not affect the results even when it was not properly conducted. The soil of the cultivation area, with annual fires, presented values of erosion responsible for the decrease of the agricultural lands.