Distribuição e caracterização química da fertilidade dos solos do estado do Amazonas.

Abstract

The soils of the Amazon tropical humid area are represented by about 75% of Oxisols and Ultisols and formed basically by two geomorphologics units, Upland ( Terra Firme a regional denomination), with a relief that varies from slightly wavy to wavy, presenting flat and dissected areas, constituted by small hills and narrows valleys that are located out of the reach of the rivers floods, with predominance of acids soils of high Al toxicity that occupy about 80% of the region. The floodplains (locally designated as Várzea ), includes areas with approximately 60,000 km2 with different fertility gradients, due to the deposition of sediments of varied mineralogical origin, organic composition and particles sizes, derived from the Andes Mountains and falling of rivers banks. The soils of Amazon are characterized by small availability of nutrients. The present study was carried out to provide more substantial data about soil fertility of Amazonas State, Brazil. Results from 3340 soil samples from all 62 counties of the State and that were collected during the past 30 years were used. In the absence of geographical coordinates, it was assumed that sampling points were uniformly scattered over each county. Chemical attributes (P, K, Ca, Mg, Al, H+Al and base saturation) showed high variability, exception made to pH and CEC. The soils of region were mainly characterized by high acidity (pH), high level of exchangeable Al and H+Al, intermediate content of organic matter and low contents of P, K, Ca and Mg. Overall, base saturation was lower than 20%, value considered low for most crops. Studies, in genetic improvement native plants with higher potential of production and soil fertility are necessary, for sustainable agriculture in Amazonas State, Brazil.