Soil Chemical Attributes of Amazonas State, Brazil

Amazonas State is the largest state in Brazil and mainly covered by tropical forest. Because of the importance of the tropical forest in maintaining soil health and a clean environment, conservation of the Amazon forest is a national priority. However, sustainable agriculture development is necessary in the state for the welfare of the local population. Maintaining soil fertility at an adequate level is an important component of sustainable farming. Very little information is available about soil fertility of Amazonas State. The objective of the present study was to evaluate chemical soil properties of Amazonas State of Brazil. Results include chemical properties of 3,340 samples, covering 62 municipalities of the state collected at 0-20cm deep during 30 years (1975-2005). Chemical properties [phosphorus (P), potassium (K) extracted with Mehlich 1, calcium (Ca), magnesium (Mg), aluminum (Al) extracted with potassium chloride (KCl) 1.0 molL-1, potential acidity (H + Al) extracted with calcium acetate, and base saturation] presented great variation, except cation exchange capacity (CEC) and pH (water). Most of the soil samples were characterized as having high acidity; medium level of organic-matter content; low levels of P, K, Ca, and Mg; and high levels of Al and H + Al. Overall, base saturation was less than 20%, a value considered very low for most of annual crops. Soils from upland areas were more acidic and have poor fertility compared with lowland soils. To maintain sustainability of cropping systems, use of an adequate level of liming and chemical fertilizers are necessary on these soils.