1. Soils Department, Federal University of Santa Maria, Avenida Roraima 1000, Santa Maria-RSSanta Maria 97105-900, Brazil.
2. Instituto Tecnológico Vale, Rua Boaventura da Silva, 955, Belém-PA 66055-090, Brazil.
3. Department of Ecology and Conservation Biology, Texas A&M University, 534 John Kimbrough Boulevard, Room 305, College Station, TX 77843-2120, USA.