Abstract: 【Objective】Newly reclaimed red soils suffer from severe acidity, low organic-matter stocks and poor nutrient availability, which severely constrain their rapid fertility build-up and sustainable use. This study evaluated how combined additions of organic amendments and calcium-based conditioners (lime and calcium salts) modulated soil acidity, carbon stabilization and crop performance, and clarified the underlying synergistic mechanisms.【Method】A field trial was established in 2023 on a newly reclaimed red soil in Ji’an, Jiangxi Province, China. Six treatments were installed: chemical fertiliser only (CK); CK plus organic amendments and 1 500 kg ha?1 calcium salt (T1); CK plus organic amendments and 3 000 kg ha?1 calcium salt (T2); CK plus organic amendments and 1 500 kg ha?1 lime (T3); CK plus organic amendments and 3 000 kg ha?1 lime (T4); and CK plus organic amendments and 7 500 kg ha?1 fermented residue (T5). Soil physico-chemical properties, nutrient availability, organic-carbon fractions, microbial biomass carbon (MBC), dissolved organic carbon (DOC), micro-structure (SEM) and rapeseed biomass were determined by physical fractionation, electron microscopy and multivariate statistics.【Result】Calcium-based conditioners significantly alleviated soil acidity and enhanced phosphorus availability. Soil pH rose by up to 16.2 % under lime treatments, while available P increased more than six-fold relative to CK. Organic amendments rapidly enlarged the soil carbon pool; total organic carbon and particulate organic carbon gained up to 84.0 % and 263.9 %, respectively. However, sole fermented residue intensified acidification and reduced carbon stability. SEM and multivariate analyses revealed that the combination of native humus with low-rate lime or medium-low-rate calcium salt promoted a porous structure, raised MBC and DOC by up to 94.6 % and 122.7 %, respectively, and simultaneously stimulated both above- and below-ground rapeseed biomass, which exceeded a seven-fold increase over CK.【Conclusion】The co-application of organic amendments and calcium-based materials effectively regulates acidity, improves phosphorus availability, stabilises organic carbon and boosts crop growth in newly reclaimed red soils. This synergistic management offers a practical pathway for rapid fertility enhancement and sustainable utilisation of such soils, and provides theoretical and technical guidance for improving cultivated-land quality in red-soil regions.