Objectives This study aimed to investigate the integrated regulatory effects of different amelioration measures on soil acidity and fertility in acidic paddy fields, providing a scientific basis for soil acidification management.

Methods A field experiment was conducted from 2021 to 2023 in an acidic paddy field in Wuhu, Anhui Province, using a randomized block design with five treatments: control (CK), lime (LM), calcium–magnesium phosphate fertilizer (CMP), Chinese milk vetch+CMP (MV+CMP), and organic fertilizer+CMP (OF+CMP). After rice harvest, soil samples were collected from the 0-20 cm layer to determine soil acidity indicators (pH, exchangeable H, exchangeable Al, exchangeable acidity), fertility parameters (organic matter, total N, available P, and available K), and rice and wheat yields were monitored. Variance analysis, principal component analysis, and correlation analysis were applied to evaluate the integrated effects of different amendments.

Results Except LM treatment, the other amendment treatments all showed an increased trend in soil fertility and yield, but a decrease trend in acid indicators with the elongation of experimental years. By 2023, in terms of fertility enhancement, compared with CK, CMP, MV+CMP, and OF+CMP significantly increased soil organic matter by 6.63%, 7.31%, and 7.78%, total N by 5.76%, 8.78%, and 7.44%, available P by 14.69%, 27.20%, and 16.34%, and available K by 12.03%, 19.21%, and 26.43% (P<0.05). MV+CMP showed the greatest effect in organic matter and total N, whereas OF+CMP achieved the highest increase in available K. In terms of crop yield, compared with CK, MV+CMP and OF+CMP significantly increased rice yield by 8.92% and 9.06%, respectively (P<0.05), CMP and OF+CMP treatment increased wheat yield by 12.39% and 17.73%, while LM showed no significant effect on yield. In terms of soil acidity improvement, compared with CK, LM, CMP, MV+CMP, and OF+CMP significantly increased soil pH by 0.34, 0.28, 0.23, and 0.26, respectively, while reducing exchangeable H by 44.19%, 28.07%, 37.68%, and 36.51%, and exchangeable Al by 31.91%, 40.99%, 33.22%, and 36.30% (P<0.05). Among these treatments, CMP was particularly effective in reducing exchangeable Al, with a further reduction of 13.33% compared with LM (P<0.05).

Conclusions CMP exhibited pronounced efficacy in mitigating soil acidification and alleviating aluminum toxicity. Notably, its combined application with green manure or organic fertilizer delivered dual benefits of "acid neutralization" and "soil fertility enhancement," addressing both the immediate stress of acidity and the long-term need for nutrient-rich soil. For single-cropping rice regions, the milk vetch incorporate combined with CMP emerges as the optimal strategy due to its significant effect on elevating soil nutrient pools. In rice-wheat rotation systems, the combination of organic fertilizer with CMP proves more suitable as it fosters steady, sustained soil fertility improvement while driving consistent, notable yield gains across both crop seasons. Collectively, the synergistic integration of organic inputs and CMP represents a sustainable solution for remediating acidic paddy soils. By simultaneously reversing acidification, reducing toxic aluminum levels, and boosting soil organic matter and nutrient availability, this approach enhances soil quality in a holistic manner, laying a robust foundation for long-term, stable crop production and food security.