Exploring peat-free nursery substrates from Amazonian agro-residues for Euterpe precatoria using multivariate and predictive approaches

Forest restoration and agroforestry expansion in the Amazon require reliable nursery systems capable of producing high-quality seedlings while reducing dependence on externally sourced growing media. This study evaluated 15 peat-free substrate formulations prepared from Brazil nut shell, acerola pit, açaí pit, cupuaçu peel and a regional commercial substrate for Euterpe precatoria seedling production and explored their performance using multivariate and predictive approaches. Principal component analysis showed that the first two components explained 75.4% of total variation, separating higher-performing formulations from substrates characterized by wider C ratios, higher electrical conductivity and greater bulk density. Exploratory factor analysis identified complementary growth, physical-structure/water-retention and chemical-buffering dimensions. The GAM-like model achieved an out-of-fold R 2 of 0.338 (RMSE = 0.776), while exploratory classification yielded an AUC of 0.62 under leave-one-mixture-out cross-validation. Brazil nut shell + acerola pit and acerola pit + commercial substrate were consistently among the highest-performing formulations, whereas pure açaí pit showed restricted seedling development. Higher-performing formulations occurred within provisional ranges of pH 4.6–6.7, C 17.0–33.9, electrical conductivity 0.1–0.6 dS m −1 , water retention capacity 120–275%, and cation exchange capacity 129–382 mmolc dm −3 . These ranges represent candidate screening benchmarks rather than validated operational thresholds. Overall, the study provides an exploratory framework for screening Amazonian agro-residues as peat-free nursery substrates and identifies formulations and physicochemical profiles requiring independent multi-site validation.