Abstract:The adaptability of plant growth in soil conditions on Chinese tropical coral islands is severely limited by the alkaline environment and soil nutrient deficiencies. Improving coral sand is essential to facilitate the rejuvenation of coral island vegetation and maintain the healthy development of the coral island ecosystem. In this study, we investigated the effects of four common soil amendment materials (vermiculite, perlite, biochar and calcium-based bentonite) on the physicochemical properties, nitrogen leaching and total nitrogen content of coral sand under the same gradient using an indoor soil column simulation test. The results showed that the application of biochar significantly reduced the pH of coral sand by 1.4% compared to the control (CK), and calcium-based bentonite, biochar, and vermiculite were able to significantly increase the cation exchange capacity of coral sand to 24.21, 10.43, and 9.43 times that of CK. Meanwhile, during the leaching process, nitrogen was rapidly leached out mainly in the form of nitrate nitrogen, and the application of biochar, calcium-based bentonite and vermiculite could not reduce the nitrogen leaching loss, but it could achieve the effect of promoting nitrogen fixation in coral sands by promoting nitrogen fixation through other pathways, which resulted in the reduction of total soil nitrogen loss under the addition of the three amendments versus CK by 40.92%, 27.32% and 25.09%, respectively. The utilization of biochar, vermiculite and calcium-based bentonite can therefore effectively improve the quality of coral sand soil, which is of great significance for the improvement of coral sand and the restoration of tropical coral island vegetation, among which biochar has the most significant improvement effect and is the ideal material for the improvement of coral sand.