We investigated the effects of cotton stalk biochar addition on the soil nutrient characteristics of alkaline paddy soil and the migration and transformation of cadmium in a soil-rice system. An outdoor pot experiment was conducted with Tefengyou 2 rice as the testing material. We added cotton stalk biochar (0%, 1%, 2.5%, and 5%) in the alkaline paddy soil with cadmium content of 0, 1, 4, and 8 mg·kg-1. After rice harvesting, the effects of different concentrations of cotton stalk biochar on alkaline soil physical and chemical properties, cadmium enrichment and transfer in rice, and the occurrence of cadmium in soil were analyzed under different concentrations of cadmium stress. The results showed that ① adding cotton stalk biochar can effectively increase soil nutrient (P<0.05). After the addition of cotton stalk biochar, the organic matter increased by 25.74%-47.53%, and the available potassium content increased by 3.16-4.25 times. ② Cotton stalk carbon can reduce the cadmium content in soil and rice, especially after the application of 5% cotton stalk carbon, The cadmium content of brown rice at Cd4 and Cd8 concentrations decreased from 0.31 mg·kg-1 and 0.43 mg·kg-1 to 0.15 mg·kg-1 and 0.10 mg·kg-1, respectively, reaching the national standard. Cotton stalk biochar can significantly reduce the enrichment and transfer coefficient of cadmium in soil-rice systems and can increase the cadmium content in the residual cadmium but decrease the acid extractable cadmium, reducible cadmium, and oxidizable cadmium content (P<0.05). ③ Soil pH, conductivity, and nutrient indicators were significantly negatively correlated with cadmium content in rice and acid extractable cadmium, reducible cadmium, and oxidizable cadmium content in soil and were positively correlated with cadmium content in residual cadmium. The above results indicate that the application of cotton stalk biochar can significantly improve the soil nutrient of alkaline cadmium-contaminated paddy soil, and the application of cotton stalk biochar has a significant control effect on the migration and transformation of cadmium in alkaline soil and rice.
Keywords: alkaline soil; bioaccumulation factor; cadmium; cotton stalk biochar; fractions of cadmium; physical and chemical properties; translocation factor.