Objective The application of lime can reduce the bioavailability of cadmium (Cd) in acid soil by adjusting pH, though the unsuitable amount can likewise have an unfavorable effect on the soil and rice production. Moreover, silicon (Si), calcium (Ca), magnesium (Mg), and phosphorus (P) are abundant in calcium-magnesium-phosphate fertilizer, however, it is yet unknown how these components relate to Cd uptake and accumulation in rice. Therefore, this study was conducted to evaluate the influence of the co-application of calcium-magnesium-phosphate fertilizer, potassium carbonate, and lime on Cd accumulation in rice as well as to investigate the interrelationship between Si, Ca, Mg, P, and Cd.

Method One control and four lime treatments were set up in this field experiment. The control group (CK) was conducted with compound fertilizer as the basic fertilizer and urea + potassium chloride as the topdressing; calcium magnesium phosphate fertilizer + urea + potassium carbonate as the base fertilizer, urea and potassium carbonate as the topdressing, then apply lime (0, 300, 450, 600 kg ha⁻¹, marked as T1 ~ T4) as the experimental group.

Result The results showed that all treatments with calcium magnesium phosphate fertilizer and potassium carbonate significantly reduced the Cd content of brown rice compared with CK. The treatment with 600 kg ha⁻¹ lime had the best effect, and the Cd content of brown rice decreased from 0.50 mg kg⁻¹ to 0.18 mg kg⁻¹, meeting the national food safety standard. The pH value of the soil increased by 0.57 units, the concentration of CaCl₂-extractable Cd in soil decreased by 41.77%, while the bioavailable Si, Ca, and Mg content increased significantly. On the other hand, the correlation fit showed that Si, Ca, Mg, and P in rice roots and straw were negatively correlated with Cd in brown rice (P < 0.05). The results of structural equation modeling showed that soil pH, as well as bioavailable Si, Ca, and Mg, were the main factors inhibiting the accumulation of Cd in brown rice, with a standardized total effect of pH > Si > Mg > Ca.

Conclusion In conclusion, calcium-magnesium-phosphate fertilizer with lime significantly reduced the risk of Cd contamination in rice grain, which increased the bioavailable Si, Ca and Mg while increasing soil pH and reducing the available Cd, thus inhibiting the Cd accumulation in rice.