Fertilization of Pinus taeda L. on an acidic oxisol in southern Brazil: growth, litter accumulation, and root exploration

Brazil has extensive areas planted with Pinus taeda L. primarily in southern areas with poor soil fertility and nutritional management. Identifying optimal management practices can be difficult since forest floor litter, along with concomitant roots, may impact tree nutrition by interacting with fertilizer/lime applications. Seeking to evaluate this interaction, a nutrient omission experiment with seven treatments was designed to evaluate mid-rotation fertilizer/lime application to a P. taeda stand in southern Brazil. The seven treatments were: complete (N, P, K, B, Zn, Cu, Mo, and lime as a Ca and Mg source); NPK omission; micronutrient omission; K omission; Zn omission; lime omission; and control. Treatments were applied when the stand was five and seven years old, followed by harvest at twelve years. Pinus taeda responded positively, with commercial volume gains of 100% (60 to 122 m 3 ha −1 ) when N and P were applied. Application of these nutrients also enhanced volume of logs in the 23–35-cm-diameter log class. No responses to K, lime (Ca and Mg), or micronutrient (Zn, Cu, B and Mo) amendments were observed. Nutrients and lime increased total litter accumulation, especially under omission of K. Roots were found in fragmented and humified forest floor layers, and omission of K enhanced total root mass (Mg ha −1 ), specific root length (m g −1 ), root length (km ha −1 ), and relative root mass (Mg Mg −1 of litter). Significant gains in P. taeda productivity on low fertility oxisols can be attained if the correct nutrients are applied at mid-rotation of these short-rotation forest systems.