1. Soil Department, Federal University of Rio Grande do Sul, Porto Alegre, Brazil
2. Engineering center, Federal University of Pelotas, Pelotas, RS, Brazil
3. Warnell School of Forestry and Natural Resources, University of Georgia, D.B. Warnell School of Forestry and Natural Resources, Athens, GA, USA
4. Agronomy Department, Federal University of Piauí, Bom Jesus, PI, Brazil