[Effects of Amendments and Straw Return on Soil and Rice Cd Content in a Rice/Rape Rotation System]

To investigate the synergistic effects of acidic soil amendments and straw return on soil properties and cadmium (Cd) content in rice under a rice/rape rotation system and to provide a scientific basis for acidic purple soil improvement and heavy metal pollution remediation, a field experiment was conducted with six treatments: no fertilization (CK), NPK (F), NPK + straw return (FT), NPK + calcium magnesium phosphate fertilizer + straw return (FGT), NPK + lime powder + straw return (FST), and NPK + biochar + straw return (FBT). The study evaluated crop yield, soil organic matter (SOM), pH, total Cd, available Cd (DTPA-Cd), and Cd content in rice straw, husk, and grains to elucidate their interactive effects. The results demonstrated that: ① Compared with CK, FGT, FST, and FBT significantly increased SOM (P < 0.05), with FBT elevating SOM by 3.56 g·kg^-1 and 9.88 g·kg^-1 during the rape and rice seasons, respectively. For crop yield, FBT enhanced rape yield by 61.7%, while FST increased rice yield by 14.4%. ② Relative to F, FGT, FST, and FBT significantly raised soil pH (P < 0.05), with FST increasing pH by 0.99 and 2.66 units in the rape and rice seasons, respectively. Compared to that in CK and F, FT increased total soil Cd by 3.1% and 1.2%, whereas FGT, FST, and FBT reduced total Cd by 9.4%-16.9% and available Cd by 23.1%-30.7%. FBT decreased Cd content in rice grains by 44.2%. ③ Cd enrichment and translocation varied across rice tissues. Enrichment coefficients followed the order straw > husk > grains, and the translocation coefficient from straw to husk was lower than that from husk to grains. ④ Correlation analysis revealed significant negative correlations (P < 0.05) between SOM and DTPA-Cd, total Cd, grain Cd, and straw Cd. In Cd-contaminated acidic purple soil under rice/rape rotation, the combined application of straw return with amendments (e.g., calcium magnesium phosphate, lime powder, biochar) significantly enhanced SOM, crop yield, and soil pH (P < 0.05) and effectively reduced available Cd and Cd content in rice tissues, with the FBT treatment (biochar combined with straw return) demonstrating the most comprehensive improvement.