Pedology, fertility, and biology of central amazonian dark earths

Abstract

A great challenge for the world's scientific community has been to find alternatives for the best use, management and conservation of the Amazonian tropical rainforest. The unbalance between increasing populations and the demand for food shows the urgency for looking for new alternatives that region, avoiding excessive degradation of natural ecosystems. In this respect, scientists in all countries in the tropics are working to understand the functioning of the rainforest and come up with alternatives to use and manage this natural resource, applying the best technology not only from an economic perspective, but principally from social and ecological perspectives. The replacement of the nutrients exported by crops is normally solved by inputs of chemical and organic fertilizers, in proportions that can vary with natural soil fertility and the nature and volume of the crops. Hence, problems like erosion, leaching, and compactation can only be solved by conservation practices utilized by farmers that change as function of land topography, precipitation, crop type, cover crop, or farming land use system, depending on the technology level of the community. Small farmers living in Manacapuru, Iranduba, Presidente Figueiredo, and Rio Preto da Eva, in Amazonas, Brazil, work on Amazonian Dark Earth (ADE) sites, cultivating vegetables and perennial crops like oranges, coconuts, cupuaçu, and others. Their land use systems include monocultures, two species mixes, and agrofor-estry systems. In general, the small farmers report that ADE is very fertile and they never need to apply chemical and organic fertilizers to get high productivity. On the other hand, studies have shown that ADE presents some nutrient limitations to plant production. Some small farmers are using large amounts of chemical and organic fertilizers and even liming unnecessarily. This intensive exploitation and the excessive use of nutrients is causing chemical degradation (Falcão et al. 2003) and even physical degradation of ADE (Teixeira and Martins 2003). © Springer Science + Business Media B.V. 2009.