[Zoning and Safe Utilization Method of Heavy Metal Contaminated Cultivated Land at Block Scale]

The safe use of arable land is one of the important measures to ensure food security and to realize the construction of ecological civilization. In order to solve the problem of blindly selecting technical measures in the process of safe use and restoration of pollution-risk cultivated land, 244 surface soil samples and 100 sets of rice-root soil samples were collected in Echi Town, Qianjiang District, Chongqing. Based on the contents of five heavy metals of Cd, Hg, Pb, As, and Cr, as well as soil oxides, organic matter, and pH and other indicators, a prediction model was established using multiple regression and geostatistical analyses, and the plots were assigned values, combined with the soil and soil in the plots. The total amount of heavy metals in the rice, the available content of heavy metals in the soil, and the pH of the soil guided suggestions for the safe use of cultivated land at the corresponding plot scale. The results showed that the soil in the study area was mainly and strongly acidic. The percentages of Cd exceeding the soil pollution risk screening value and control value were 33.61% and 2.05%, respectively. The effective content of Cd accounted for 60%, and the Cd exceeding rate of rice was 28%. There was an obvious ecological risk of Cd in the study area. The available Cd content of the soil was mainly affected by the total amount of soil Cd and pH. The enrichment of Cd in rice was mainly affected by the content of soil organic matter, Mn, and CaO. The zoning results showed that the priority protection category of the soil in the study area accounted for 59.30%; the safe use category accounted for 40.44%, of which safe use (IAa), safe use (IAb), safe use (IBa), safe use (IIAa), safe use (IIAb), and safe use (IIBa) accounted for 19.49%, 8.01%, 1.43%, 7.04%, 1.41%, and 3.06%, respectively; and strict control accounted for 0.26%. This method combined the safety risks of soil and agricultural products and aided formation of specific recommendations for safe use, which provided a method of reference for the safe use of contaminated farmland in accordance with local conditions.