In the southern highland (Planalto Sul) region of Santa Catarina, Brazil, most of the pine forests were planted without soil fertilization. Currently, many areas are in the second or third rotation, and their productivity may be limited by low soil fertility. An alternative to mitigate this problem would be fertilization in the established forest. This study was carried out with the objective of evaluating the effect of fertilization with N, P, and K at different growth stages of Pinus taeda. Experiments were conducted in one-, five-, and nine-year-old forests, all in the second rotation, in Cambisols located in the municipality of Otacílio Costa, Santa Catarina, Brazil. Treatments consisted of combinations of fertilization rates of N (N0=0, N1=70, and N2=140 kg ha-1 N), P (P0=0, P1=75, and P2=150 kg ha-1 P2O5), and K (K0=0, K1=60, and K2=120 kg ha-1 K2O), plus a control treatment without fertilization. The combinations used were N0P0K0, N0P1K0, N1P1K1, N1P2K1, N1P2K2, and N2P2K1. A completely randomized block experimental design was used, with three replications. The height and diameter at the root collar or at breast height of trees was measured; also the trunk volume of the plants and N, P, and K contents in needles at six and 18 months after fertilization were measured. In one-year-old plants, a significant increase in timber volume was obtained with the application of 70 kg ha-1 of P2O5. For five- and nine-year-old plants, fertilization with 70, 75, and 60 kg ha-1 of N, P2O5, and K2O, respectively, promote significant increase in timber volume, showing that fertilization of established pine forests increase productivity in areas of low fertility.
nutrients; application times; productivity
