Comparative Dynamics of Nutrient Release through Litter Decomposition in Eucalyptus grandis Hill ex Maiden and Pinus taeda L. Stands

The installation of commercial stands with exotic forest species on low fertility soils originally covered by native pastures is an unusual situation worldwide. In recent years, the area occupied by forest systems designed for pulp or wood production with immediate replanting has increased strongly in the Pampean region of South America. In this context, the study of nutrient recycling from forest litter decomposition acquires particular relevance. This work seeks to evaluate and compare the nutrient release from the decomposition of forest litter produced by 14-year-old Eucalyptus grandis Hill ex Maiden and Pinus taeda L. stands and test the applicability of a new sampling methodology in the nutrient recycling assessment. For two years, the evaluation of N, P, K, Ca, Mg, Fe, Mn, Cu and Zn dynamics during litter decomposition was carried out. In general, K concentration decreased through decomposition, meanwhile, all other nutrients showed some degree of immobilization, but this was counteracted by biomass loss for most of them. This mainly resulted in net nutrient release from litter. A higher release rate of all nutrients from P. taeda forest litter compared to E. grandis, with the exception of Mn, was verified. Fe immobilization was observed in both species showing a higher immobilization rate in E. grandis compared to P. taeda. Finally, Zn exhibited immobilization processes in E. grandis and releases in P. taeda. This might suggest higher temporal and quantitative availability of nutrients in P. taeda, due their faster return to the soil. These findings could be relevant in the development of models for sustainable management, adapting the demand for nutrients to the supply during forest rotations.