Estimates of deforestation in the Brazilian Amazon, primarily for shifting cultivation and pastures, exceed the land area for the State of Rondônia. An experiment was conducted on a Xanthic Hapludox near Manaus, Brazil to establish soil nutrient depletion patterns and fertilizer and lime requirements for continuous cultivation after slash-and-burn clearing. Yield responses to N, P, K, Mg, S, B, Cu, Mn, Zn and lime were evaluated during eight years of cultivation. Seventeen crops were grown during the period from 1981 to 1990, and yield responses were detected for P, K, lime and Mg beginning with the first, second, third and 11 th crops, respectively. Only corn crops responded to N and the requirements increased with each crop. In the absence of fertilizer and lime soil N, P, K, Ca, Mg, C and pH decreased and percent Al saturation increased with time of cultivation. Mean crop yields, with liming and fertilization based on soil analyses, were 4.1 t ha-1 yr-1 as opposed to 0.2 t ha-1 yr-1 in the check treatment. Total grain yields obtained from 1 ha, during eight years with adequate fertilizer and lime management, would correspond to yields from 24 ha of land under shifting cultivation practices.
humid tropics; Oxisol; deforestation; shifting cultivation; sustainable agriculture