Chemical characteristics of soils of a toposequence under pasture in front of a pioneering Eastern Amazon

Abstract

The occupation of the Amazon in a disorderly manner with the replacement of forests by
crops or pastures, whose management has been inadequate, has led to degradation of large areas
by changes in soil attributes. Aiming to evaluate changes in chemical attributes
soil in relation to relief position, a study was carried out near Maraba (PA) in an area
with pasture (Brachiaria Brizantha), aged four years. The area was subjected to traditional preparation practices, with clearing and burning of primary forest biomass and the first year with rice cultivation. Grassland ecosystem, grazing by cattle and burned as management of the area were conducted. Samples were taken from vertical sections, the top, slope and low slope, in a sequence with 300 m long. The results showed a decrease of the elements (P, K, Ca, Mg, Na) with increasing soil depth. In the case of P, there are increased levels of the area with fragments of the source material. The distribution of phosphorus followed the content of organic matter in different soil types along the toposequence in
order Oxisol <Cambisol <Gleissolo. The low amounts of bases and the high content of aluminum in the exchange complex indicate a high degree of weathering of soils.