During the past several decades, extensive areas of the humid tropical Amazon have been cleared for the introduction of pasture or subsistence farming and later abandoned after a few years of use. An option for recovering these areas is the planting of rubber trees because it is a native tree that could restore conditions similar to those existing before the clearing. In addition, the high economic value of natural rubber is a source of income for small producers. In soil management under the Amazon conditions, low phosphorus (P) has been the most limiting factor. Under natural conditions, P is provided to the plants almost exclusively by organic matter mineralization. The aim of this study was to evaluate a chronosequence of reforestation with rubber trees planted at different times in cleared areas, with primary forest as a reference. The amounts of litter and P content in the plant, in the litter, and in soil, as well as biological indicators (acid and alkaline phosphatase and P microbial biomass) associated with the P cycle in a Xanthic Ferralsol (Oxisol), in the Central Amazon were assessed. Rubber tree growth resulted in changes in total organic carbon, with an increase of 104.6% in the 45-year-old rubber trees compared with the 6-year-old rubber tree plantation. This was also observed for acid and alkaline phosphatase activities, which were close to those of the primary forest. The formation of litter and the P content of the microbial biomass in soil were higher in rubber areas. The P immobilized into microbial biomass was the main reserve to meet the plant's nutritional demand for phosphorus. The content of P available in the soil, regardless of the extractants (Mehlich 1, Mehlich 3, and Bray 1) and the age of vegetation cover were below the levels indicated as appropriate.
1 Embrapa Soybean, Paraná State, Brazil.
2 Federal University of Amazonas, Amazonas State, Brazil.
3 Estadual University of Londrina, Paraná State, Brazil.
Address for correspondence: Dr. Adônis Moreira, Embrapa Soybean, Caixa Postal 231, 86001-970, Londrina, Paraná State, Brazil. E-mail: firstname.lastname@example.org
Financial Disclosures/Conflicts of Interest: This study was supported by CNPq (National Counsel of Technological and Scientific Development).
Received August 30, 2013.
Accepted for publication December 12, 2013.