Optimizing Performance of Eucalyptus Clones With Nutrient Balance Approach : Quantifying and Evaluating Responses In Typic Kandiudult

Abstract

Eucalyptus plantations in Riau Province, which serve as the backbone of Indonesia's pulp industry, face declining productivity challenges due to soil fertility degradation. The dominant soil in this region is Typic Kandiudults, characterized by strongly acidic pH (3.4-4.7), high aluminium toxicity, and very low levels of essential nutrients such as phosphorus (P) and potassium (K). These conditions are exacerbated by long-term intensive monoculture practices. Meanwhile, dependence on volatile imported fertilizers demands higher nutrient use efficiency. Conventional uniform fertilization approaches for all clones are deemed ineffective, necessitating precision strategies that consider the specific physiological characteristics of each Eucalyptus clone. This research aims to quantify nutrient uptake and efficiency of each Eucalyptus clone based on total biomass, quantify the nutrient contribution of harvest residues returned to the soil, and validate the effectiveness of the Nutrient Balance (NB) approach based on field trial results. The study was conducted in two phases. The first phase involved destructive biomass sampling of five superior Eucalyptus clones (Pelita 1, Pelita 2, Grandis Pelita 1, 2, and 3) at harvest age of 5 years. Samples were analysed to calculate Biological Utilization Coefficient (BUC) and Nutrient Use Efficiency (NUE). The second phase was field validation using the twin plot method, where NB-based fertilization plots were compared with standard operational procedure (SOP) plots on Pelita 1 clone over one full rotation. The results revealed significant physiological variation among clones. BUC analysis showed differences in nutrient acquisition efficiency and recycling contribution. Grandis Pelita 3 stood out with the highest BUC-Left on Site for K (0.16) and Ca (0.16), indicating its superior ability to recycle nutrients. Meanwhile, NUE analysis revealed highly varied efficiency in converting nutrients into biomass. Pelita 2 and Grandis Pelita 2 showed the best NUE for P (9628 and 9069 kg biomass/kg P respectively) and Mg. Conversely, Grandis Pelita 1 showed unfavourable specialization for P-deficient soils, with the lowest P NUE (2184 kg biomass/kg P) despite its high N NUE. This data proves that each clone has unique physiological strategies in facing nutrient stress. Another key finding is the vital contribution of harvest residues to nutrient cycling. BUC-Left on Site values showed that harvest residues return 16-41% of absorbed P and 14-16% of absorbed K back to the soil. This makes residues not just waste, but a crucial recycled nutrient source for production system sustainability, while reducing dependence on external fertilizers. The integration of BUC and NUE data then became the foundation for the Nutrient Balance (NB) approach. The NB approach calculates precise fertilizer doses by considering initial soil nutrient status, production targets, and the specific clone's acquisition (BUC) and conversion (NUE) efficiency. Field validation on Pelita 1 clone proved the effectiveness of this approach. NB-based fertilization successfully achieved high productivity targets (MAI 50) with 25% better input efficiency compared to SOP fertilization. This success demonstrates that meeting nutrient requirements based on the clone's physiological characteristics is superior to general dose application. Overall, this research successfully developed and validated an integrated BUC-NUE-NB framework for precision nutrient management. This framework transforms biomass and nutrient data into powerful predictive and prescriptive tools. The practical implication of these findings is the opportunity for industry players to implement different management strategies for each clone type. High-recycling clones like Grandis Pelita 3 are suitable for low-input systems, efficient clones like Pelita 2 for maximum productivity targets, while specialized clones require specific interventions. Thus, this research contributes not only to productivity enhancement but also to environmental sustainability and production cost efficiency in Eucalyptus plantations on Indonesia's marginal soils.