Abstract:
Aiming at the problem of cadmium (Cd) pollution in paddy fields in the acidic red soil region of southern China, this study took a typical cadmium-contaminated rice-growing area in Hengyang City, Hunan Province as the object, and comprehensively evaluated the effects of five measures, including clean water irrigation (T1), sedimentation and source interception (T2), straw returning (T3), straw removal (T4), and lime application (T5) on the accumulation and transformation of Cd in the soil-rice system. The five-year field experiment shows that the atmospheric deposition flux of cadmium in the experimental area exhibits obvious monthly dynamic differences. Dry and wet deposition is the main way of deposition, with a monthly average of 0.15 mg·m
−2. The cadmium deposition flux in summer half year is 3 ~ 5 times higher than that in winter half year, and the annual average decrease of cadmium flux from 2017 to 2019 is 21.6%. Lime treatment increases soil pH from 5.47 to 6.26, facilitating the transformation of cadmium to residual state. Lime treatment increases the proportion of residual state from 17% to 35%, decreases cadmium activity with 78.8% reduction of cadmium content in roots and 60.0% - 80.0% reduction in grains; which significantly reduces the enrichment of cadmium in rice plants by 46.3% - 80.0%. Compared with the initial value (0.41 mg·kg
−1), the total cadmium content in the surface soil is decreased by 12.1% and 10.5% under clean water irrigation and straw removal, respectively; while the straw returning group is increased by 9.3%. Straw removal from the field could effectively reduce the accumulation of cadmium in stems and grains with 43.0% reduction of cadmium content in roots. Atmospheric deposition could significantly reduce the accumulation of cadmium in the aboveground part of rice. Straw returning could lead to the migration of cadmium from root to aboveground part, and increase the accumulation of cadmium in root and stem. The atmospheric deposition process may be an important source of cadmium in soil and rice in cadmium-contaminated areas. The applications of lime and purification of irrigation water in farmland in cadmium-contaminated areas are the technical practices for the safe use of farmland soil.