1. Dep. of Soil Science; Univ. de São Paulo; CP 9 13418-900 Piracicaba São Paulo Brazil
2. CP 39 68625-000 Paragominas Pará Brazil
3. Dep. of Soil Science and Agricultural Engineering; Univ. Estadual de Ponta Grossa; Av. Gen. Carlos Cavalvanti, 4748 84030-900 Ponta Grossa Paraná Brazil
4. Instituto Federal Catarinense; Campus Sombrio Rua das Rosas, s/n 88965-000 Santa rosa do Sul Santa Catarina Brazil