This study addressed the constraints of salinity–alkalinity stress on sustainable agricultural development by conducting a two-year field experiment to investigate the ameliorative effects of different treatments on soda alkaline soil, including chemical fertilizer alone (CK), decomposed straw (S), decomposed straw combined with woody peat (SP), biochar (SC), and organic fertilizer (SO). Five treatments were established, and soil physicochemical properties, aggregate composition, microbial biomass carbon (MBC), and crop responses were systematically measured under each treatment. The nitrogen harvest index (NHI) was calculated, and alkalinity reduction efficiency was ranked. Furthermore, clustering heatmaps and principal component analysis were employed to comprehensively evaluate the amelioration effects of different amendments on soda salinity–alkalinity soil. The results showed that compared with CK, the SP treatment significantly reduced soil pH, exchangeable sodium percentage (ESP), and salinity by 6.56%, 50.04%, and 37.84%, respectively. In addition, SP optimized aggregate structure by promoting the accumulation of readily oxidizable organic carbon (ROC) and enhancing microbial activity (MBC), ultimately achieving efficient nitrogen utilization in crops, with an NHI of 65.76%. Although the SO treatment achieved the highest rice yield (11,504 kg/hm2) by stimulating the turnover of dissolved organic carbon (DOC), it also posed a higher risk of carbon loss. The SC treatment exhibited a remarkable carbon sequestration effect but carried the risk of exacerbating soil alkalization. Overall, the findings indicate that different amelioration strategies can be selected according to specific goals, such as “short-term high yield” or “high-quality sustainability”, thereby providing important theoretical support and practical guidance for precise and targeted reclamation of salinity–alkalinity soils.