Objective  The effects of applying calcium (Ca) and magnesium (Mg) fertilizers on the quality and soil nutrients of integrative rice and shrimp system in paddy field were assessed, aiming to provide supports for the research of special fertilizer and high-efficiency management technology models on integrative rice and shrimp systems.

  Method  This experiment consisted of five treatments, namely conventional fertilization (Farmer Practice, FP), different dosages of Ca and Mg fertilizers (Optimized Treatments, OPT1, OPT2, OPT3), and controlled-release fertilizer treatment (OPT4). The total amount of Ca and Mg in OPT1-OPT3 were 50.4, 45.0 and 54.9 kg hm⁻², respectively, with reference to conventional application rates in paddy field.

  Result  The results indicated that adding appropriate fertilizer rates of Ca and Mg could not significantly improve the rice yield and shrimp yield compared with FP. Under different management conditions, the yields of rice and crayfish were 4176.11-4567.38 kg hm⁻² and 1740-2055 kg hm⁻², respectively. However, the application of Ca and Mg fertilizer could significantly improve the quality of rice and crayfish. The chalkiness and chalkiness rate of OPT3 rice decreased significantly (P < 0.05) by 71.43% and 50.74%. The gel consistency and protein increased significantly (P < 0.05) by 9.21% and 11.6%. Meanwhile, the Mg, protein and amino acid contents of crayfish increased significantly (P < 0.05) by 11.63%, 15.42%, and 8.57% compared with FP, respectively. In addition, this study found that the application of Ca and Mg fertilizers could significantly increase the soil exchangeable Ca content (P < 0.05), the OPT3 was the highest, reaching 3.19 cmol kg⁻¹, 29.15% higher than FP.

  Conclusion  In conclusion, it can be seen that the application of an appropriate amount of Ca and Mg fertilizer has an obvious effect on improving the quality of rice and shrimp, especially in OPT3 treatment, with 54.9 kg hm⁻² of Ca and Mg fertilizer application rates.