Nitrogen, phosphorus, and potassium requirements for Eucalyptus urograndis plantations in southern Brazil

Although areas planted with eucalyptus have increased under the subtropical conditions of southern Brazil, fertilization has followed practices from nearby tropical regions. The objective of this study was to determine the response of Eucalyptus urograndis to N, P, and K in two regions of Parana State (Jaguariaiva and Ventania) on a sandy oxisol following two harvest cycles of Pinus taeda. Site preparation prior to the new experiment included the application of rock phosphate (26.2 kg ha(-1) of P) by in-row subsoiling. Five rates of N and P (0, 13, 26, 52, and 105 kg ha(-1)) and K (0, 29, 58, 116, and 232 kg ha(-1)) were separately tested. Treatment response was evaluated by determining maximum technical efficiency, height, and diameter at breast height (DBH) at 3, 6, 9, 12, 18, 24, 30, and 36 months after planting, and volume at 36 months. At all assessments, N additions did not influence growth parameters indicating that N demands were met by organic matter/litter mineralization. Phosphorus enhanced growth until the 18th month, with maximum gains at months 9 and 6 for Jaguariaiva and Ventania (56 and 59% of DBH for the 105 kg ha(-1) P rate, respectively). Potassium improved growth only after the 24th month; maximum rate occurred at 166 kg ha(-1) of K with a volume of 163 m(3) ha(-1) at the Jaguariaiva site at 36 months. In conclusion, findings indicated that Eucalyptus urograndis grown in southern Brazil could be responsive to P and K fertilization, but not to the addition of N fertilizer.