The Effects of the Combined Application of Biochar and Phosphogypsum on the Physicochemical Properties of Cd-Contaminated Soil and the Yield Quality of Chinese Cabbage

Chinese cabbage ( Brassica pekinensis (Lour.) Rupr.) is rich in many vitamins and many minerals and is an important green vegetable in people’s daily diet. Soil heavy metal Cd content exceeding safe values has a toxic effect on the growth of vegetables, which seriously affects human health. Biochar can effectively stabilize heavy metals in polluted soil, and phosphogypsum can improve the physical and chemical properties of soil and promote the growth of crops. To explore the remediation effect of biochar combined with different amounts of phosphogypsum on Cd-contaminated soil and the safe production of agricultural products, a pot experiment was conducted with corn straw biochar and harmless phosphogypsum as the test materials, and Chinese cabbage as the test plant. The soil pH; the alkali-hydrolyzed nitrogen content; the available phosphorus, potassium, and Cd content in the soil; the fresh weight of the Chinese cabbage; the Cd content in the edible part of the Chinese cabbage; and the vitamin C, chlorophyll, and soluble sugar contents in the leaves were measured and analyzed. The results showed that among all the treatments, the T3 and T4 treatments were the most effective in enhancing the soil pH and soil available nutrient content. Compared with CK, the T3 and T4 treatments significantly enhanced the soil pH by 0.27 and 0.29 units, respectively, and significantly increased alkali-hydrolyzed nitrogen content by 16.25% and 14.04%, available phosphorus content by 22.98% and 22.87%; and available potassium content by 8.50% and 10.13%. In addition, among all the treatments, the T3 treatment had the best effect on reducing the soil available Cd content and the Cd content in the edible part of the Chinese cabbage, which were significantly reduced by 17.05% and 49.35%, respectively, compared with CK, and the T3 treatment had the best effect on improving the yield and quality of the Chinese cabbage, significantly increasing the fresh weight of the Chinese cabbage by 31.86%, the soluble sugar level by 9.54%, the vitamin C level by 15.38%, and the chlorophyll level by 13.28%, compared with CK. In summary, 3000 kg/hm 2 of biochar combined with 3000 kg/hm 2 of phosphogypsum can significantly reduce the effectiveness of soil Cd, prevent the transfer of Cd to Chinese cabbage, reduce the ecological risk of Cd, and improve the yield and quality of Chinese cabbage. The results provide a theoretical basis for the safe production of agricultural products in Cd-contaminated soil and promote the recycling of resources for the benefit of the environment.