SOIL PROPERTIES DYNAMICS INDUCED BY PASSAGE OF FIRE DURING AGRICULTURAL BURNING

Characteristics of an ecosystem are altered both as sudden modifications induced by the passage of the fire and the delayed changes derived from the simultaneous modifications of various soil physical and chemical parameters. Effects of fire on soil properties was performed in experimental plots, whose fuel amount was altered in order to obtain different heating intensities with the aim of determining changes in the soil physico-chemical parameters at varying heating temperatures. The research was conducted in a continuous cropped arable experimental plots located at the University of Uyo Teaching and Research Farm (UUTRF), Use-Offot, Uyo, Nigeria for four growing seasons, between March, 2010 to October, 2011. Core and bulk samples from the burned and adjacent unburned plots (control) were collected for physico-chemical analysis using standard procedures. These induced temperatures were highly variable on the soil surface. Temperature differences significantly (P < 0.05) affected sand, total nitrogen, organic carbon and pH contents of the soils positively (r = 0.518, 0.478, 0.582, 0.595 respectively), whereas a reduction in the soil temperature increased the concentrations of clay, 1mm, 0.05mm and 0.25 mm stable soil aggregates in the soil (r = -0.619, -0.578, -0.780, -0.526 respectively) after burning. Exchange acidity increased to 5.12 cmolkg-1 at 400C from 0.80 cmolkg-1 at initial temperature of 250C at the surface soil. Though aggregates formation was significantly higher (P = 0.05) after burning than the control soil locations, this soil will easily be distressed with the least application of force. The pH decreased to 5.4 at higher temperatures following burning before ashes mineralized. However, both organic matter and ECEC increased at increasing soil temperature. Potassium content remained surprisingly constant as the soil temperature increased. Despite the merits of quick release of occluded nutrients, heating temperatures of slash-and-burn method of land clearing altered soil quality attributes.