Objective The aim was to investigate the effects and safety of continuous application of soil conditioners on acidic soil.

Method This study compared the efficacy of quicklime and two novel conditioners (ST and MT), with a no-conditioner control, on soil amelioration. A water spinach cultivation trial was conducted to validate the safety of the long-term application.

Result Compared with no conditioner application, continuous applications of the new types of soil conditioner significantly increased soil pH by 0.61-2.39 units, increased alkali-hydrolyzed nitrogen by 0.75% - 10.89%, and markedly increased available phosphorus by 38.62% - 222.89%. Concurrently, water spinach yield increased significantly by 120.81% and 132.64%, with improvements in nutrient accumulation and agronomic traits. Compared to traditional quicklime, the novel conditioners were more effective in increasing alkali-hydrolyzed nitrogen (2.97% - 8.22%) and available phosphorus (9.39% - 186.19%). They also reduced soil bulk density, increased the proportion of macro-aggregates, and enhanced water spinach yield and nutrient accumulation. Between the two novel conditioners, MT demonstrated superior overall performance in improving agronomic traits, nutrient accumulation and yield of water spinach compared with ST.

Conclusion Continuous application of the novel soil conditioners safely and effectively ameliorates acidic soil while enhancing crop productivity, and MT conditioner shows the best overall performance and promising potential for widespread adoption.