Integrated Nutrient Management Improves Potato Growth, Yield Components, and Phosphorus Use Efficiency Across Contrasting Acidic Tropical Soils

Weathered acidic soils are characterized by severe phosphorus (P) fixation and aluminum (Al3+) toxicity, limiting crop productivity. Integrated nutrient management (INM), combining mineral fertilizers, organic amendments, and biofertilizers, offers a promising strategy to overcome these constraints. Unlike conventional single-site fertilizer comparisons, this study examined how mineral, organic, and phosphate-solubilizing biological inputs interact with contrasting acidic soil environments across successive seasons, allowing simultaneous assessment of immediate crop productivity and residual soil fertility. Field experiments were conducted over two consecutive cropping seasons (2022–2023 and 2023–2024) at three sites in Tete Province, Mozambique: Ntengo-wa-mbalame, Rinzi, and Angónia Research and Technology Transfer Centre (CITTA). The experiment followed a 2 × 3 × 11 factorial arrangement in a randomized complete block design with four replications. Eleven treatments comprising mineral N, P, K, and S fertilizers, vermicompost, and a multifunctional multi-strain phosphate-solubilizing biofertilizer (Bio-Rock P) were evaluated. Soil chemical properties and crop performance were influenced by site and season (p ≤ 0.001). Ntengo-wa-mbalame had the most favorable fertility, achieving a maximum yield of 34.96 t ha−1 in Year 1, whereas high acidity and exchangeable Al at Rinzi restricted canopy development and increased small, non-commercial tubers (<45 mm). Across sites, exclusive mineral fertilization showed numerical trends toward greater soil pH declines (up to 26%), whereas INM treatments maintained more stable soil pH levels (declines limited to 2.2–10.8%) and significantly reduced toxic exchangeable Al3+ down to 0.03 cmolc kg−1, likely through organo-metallic complexation. Treatments combining mineral inputs, vermicompost, and biofertilizers, particularly T7, showed strong residual effects, increasing available P from 55.34 to 87.02 mg kg−1 by Year 2 while maintaining marketable tuber yields and nutrient recovery statistically comparable to or exceeding mineral fertilization. PCA showed that P agronomic efficiency (P-AE) was positively associated with biomass, tuber number, and total tuber yield. Overall, INM improved nutrient availability, moderated soil acidity and Al toxicity, and supported potato productivity, providing an ecologically sustainable strategy for fragile tropical agrosystems.