Sediments carried away by the muddy waters of the Guamá River and the heterogeneity of these substances are responsible for the soil formation and diversity of chemical characteristics in the periodically flooded areas. This study aimed at determining the physical and chemical attributes of a low floodplain (varzea) soil of the Guamá river, in different periods, cultivated with Paramaribo canarana (Echinochloa polystachya H.B.K) or canarana erecta lisa (Echinochloa pyramidales Lam). The experimental design was entirely randomized, in a 4 x 4 factorial scheme (4 depths and 4 sampling periods) with 6 replications. Composite soil samples were collected at six equidistant points from a transection, at depths of 0-10, 10-20, 20-30, and 30-40 cm in May, August and November/2002 and February/2003. Soil texture, organic matter, pH in H2O, pH in KCl, extractable P, exchangeable K, Al, Ca, and Mg and the micronutrients Cu, Mn, Zn, and Fe were determined. The soil of the area under study is classified as Gleysol, i.e., little developement, poorly drained, normally acid, with a silt- clay-loam horizon. The soil chemistry composition was affected by seasonality. During the rainy season and when the most intense flooding occurred in the floodplain, in February, the pH, Cu and soluble iron concentrations increased and Mg and exchangeable aluminum decreased. During lower soil humidity periods base saturation and CTC were higher. Iron was the nutrient that showed the greatest variation in the flooded soil; the increases exceeded 1000 % during the period of more pronounced flooding (February).
Soil fertility; seasonality; Echinochloa polystachya; Echinochloa pyramidalis
