SOIL PROPERTIES AND THEIR VARIATIONS ON 2 CONTIGUOUS HILLSLOPES IN NORTHEAST BRAZIL

Information on spatial distribution of soil properties in a landscape is not only required for soil mapping and classification but also for soil management. Spatial patterns of soil properties in a landscape ar e the results of systematic variations in pedogenic processes controll ed by environmental factors of which landscape position is important. In northeast Brazil, Lithosols (Ustorthents) whose surface horizons ar e directly underlain by lithic or paralithic contacts occupy upper slo pe positions with steep gradient; the Cambisols (Ustropepts) occupy th e mid- and lower slope positions. In some cases Non-Calcic Brown soils /Planosol (Haplustalfs) occupy lower slopes. We examined the propertie s of two contiguous hillslopes in granitic and gneissic saprolite to d etermine whether there were any systematic variations among landscape positions and to interpret pedogenesis in the hillslopes. Particle siz e distribution, and the Ti content of sand plus silt and saprolite sho wed that the two hillslopes were formed on different parent materials. At Site 1, soil property variations along the slope, measured by stan dard deviation from the means, were attributed to variability in paren t material rather than to landscape position. Except for solum thickne ss, which increased systematically downslope, variations in sand, clay , ECEC and pH were not related to landscape position. Increasing solum thickness downslope was explained by the effect of erosion on the upp er, and deposition at the lower slopes. Silt and organic carbon conten ts at Site 1, and Fe-o and Fe-d contents at Site 2 significantly decre ased downslope. One possible explanation for this trend, in addition t o erosion and deposition, is the effect of slash and burn agriculture on the lower slopes, and the changes in redox conditions caused by per iodic waterlogging.