Objective The acidification materials were used to intensify soil acidification and the impacts of changes in soil pH on Cd activity in soil and rice yield and quality after acidification of Cd contaminated soil were explored, with a view to providing theoretical support for the remediation of Cd contaminated soil.

Method Through a soil culture experiment, the dynamic changes of soil pH and available Cd content in Cd contaminated soil after application of acidification materials were analyzed to explore the impacts of soil pH changes on Cd activity. By using a rice pot experiment, the effects of soil pH reduction on rice yield and quality were explored by analyzing the changes in rice biomass, yield and its components, Cd contents of rice plants and rice after soil acidification.

Result The application of acidification materials can accurately reduce soil pH and form a certain pH gradient in the test soil. The soil pH values decreased by 0.33 and 0.67 units, and the soil available Cd contents increased by 0.04 and 0.07 mg/kg, respectively, with an increase of 21.05% and 36.84%. There was a significant negative correlation between soil available Cd and soil pH. The decrease in soil pH resulted in the inhibition of rice growth and plant emaciation. Compared with CK, the aboveground biomass of rice under pH 4.77 and pH 5.11 treatments decreased by 9.61% and 2.48%, respectively. Moreover, the effective number of panicles and filled grains, and seed setting rate of rice decreased with the decrease of soil pH, resulting in a decrease of 11.58% and 1.74% in the rice yield of pH 4.77 and pH 5.11 treatments compared with CK. Soil acidification led to the activation of heavy metals, resulting in an enhanced ability of rice plants and rice to enrich Cd. The Cd content of pH 4.77 and pH 5.11 plants increased by 87.52% and 1.13% compared with CK, respectively, while the Cd content of rice increased by 134.55% and 165.45% compared with CK.

Conclusion Soil pH affects the form of Cd, and soil acidification increases the bioavailability of Cd. There is a significant negative correlation between soil available Cd and soil pH. Soil acidification impedes the growth of rice, reduces biomass in the above ground parts, decreases the number of panicles and filled grains, and reduces yield. Acidification also increases soil Cd activity, enhances ability of rice to absorb and enrich Cd, and increases the risk of heavy metal pollution correspondingly.