Study On The Stabilization,Phytoextraction,and Crop-Safe Production Of Typical Cadmium High Geological Background Soils From Eastern Yunnan

High geochemical background soils are widely distributed in the agricultural areas of south and southwest China.The characteristics of cadmium(Cd)enrichment in high geological background soils in the agricultural land differ greatly from those of the anthropogenically contaminated soils.High-Cd geological background agricultural soils show characteristically diverse enrichment types and complex pollution sources,leading to large-scale Cd pollution in rice and potential health risk to consumers.Yunnan province is a typical high geological background area with a high Cd pollution risk.However,few studies have addressed the stabilization and phytoextraction of metals from high geological background soils.Here,the aim was to investigate(1)soil pH,soil nutrients,and potentially toxic metal pollution in soils and edible parts of local major hot pepper and rice cultivars,and further develop soil Cd safety thresholds for hot pepper and rice production in the high-Cd geological area in a field study;(2)Cd stabilization efficiency of the high Cd geological soils in a field plot experiment;and(3)Cd phytoextraction efficiency of the high-Cd soils by the Cd/zinc(Zn)hyperaccumulator Sedum plumbizincicola and the resulting Cd uptake by rice to provide further understanding of the efficiencies and mechanisms of different strategies to remediate high geological soils for safe crop production.The main results are as follows.1.A field investigation was conducted and the physicochemical properties and Cd pollution characteristics of the high-Cd geological soils in Shilin County,Yunnan province,southwest China were analyzed.The agricultural soils in Shilin were acid.The Cd concentration in the agricultural soils was 10.6 times the baseline value.The soils showed Cd enrichment as well as the metalloid arsenic(As)and lead(Pb)enrichment with high metal(loid)concentrations but low availability.Cadmium concentrations in the edible parts of 21 cultivars of hot pepper and 3 rice cultivars exceeded the GB 2672-2022 limits.2.A field plot experiment was carried out to investigate the effects of different application rates of calcium carbonate,selenium fertilizer,and organic fertilizer on soil Cd availability and Cd accumulation in upland rice and hot pepper.As expected,calcium carbonate application significantly increased soil pH.The HCl-Cd concentrations in soils decreased with increasing application rate of calcium carbonate,together with significant decreases in Cd concentrations in the edible parts of rice and hot pepper.No significant effect was observed using other remediation treatments.3.Pot experiments were conducted to investigate Cd phytoextraction efficiency of the high geological background soils from Shilin,Fuyuan,and Luoping in Yunnan province by the Cd/Zn hyperaccumulator S.plumbizincicola.After three seasons of S.plumbizincicola growth the phytoextraction efficiencies of the soils from Shilin,Fuyuan,and Luoping were 30.4,50.4,and 67.4%(Cd)and 9.7,5.1,and 18.3%(Zn),respectively.Sedum plumbizincicola grew better when grown in soils from Fuyuan and a greater Cd phytoextraction efficiency when grown in soils from Shilin.The total and available Cd concentrations in soils showed a substantial decrease after three seasons of S.plumbizincicola growth.After subsequent rice cultivation the Cd concentrations in brown rice and rice straw decreased greatly under flooded conditions throughout the growth period,thus contributing to safe crop production.