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【Objective】The present paper aimed to study the occurrence form of cadmium (Cd) accumulation in soil aggregates of Cd-contaminated brown calcareous soil matrices of paddy fields in the Karst area of northwestern Guangxi, and to provide data reference for safe rice production in this type of Cd-contaminated paddy fields in the region. 【Method】The sampled soil aggregates were separated into five aggregates as ＞ 2.000 mm, 1.000-2.000 mm, 0.050-1.000 mm, 0.074-0.250 mm and ＜0.074 mm, the composition of soil aggregates particle size, Cd content of different particle size aggregates and their main occurrence patterns from 0-20, 20-30, 30-50 and 50-80 cm depth profiles in the Karst area of northwest Guangxi were studied.【Result】The proportion of 0.250-1.000 mm size aggregates in each profile was stable, above 30.00%, with no significant difference between profiles (P＞0.05), the proportion of ＞2.000 mm size aggregates in the 0-20 cm soil profile (tillage layer) was the largest (40.20%), and as the depth of the profile increased, the proportion of ＞2.000 mm size aggregates decreased rapidly, and the proportion of ＜0.250 mm size aggregates showed a gradual increasing trend. Analysis of the Cd content of agglomerates of different particle sizes showed that, in 0-20, 20-30 and 30-50 cm soil profiles, Cd was mainly enriched in ＞2.000 mm particle size aggregates, with contents as high as 2.22, 1.66 and 0.95 mg/kg, respectively, and in the 50-80 cm soil profile, Cd was mainly enriched in 1.000-2.000 mm particle size aggregates. ＞2.000 mm particle size aggregates contributed most to the whole soil Cd content in the 0-30 cm soil layer. The occurrence form of Cd in the aggregates at different profile depths showed obvious differences, the proportion of Cd in aggregates of all particle sizes in the 0-20 cm profile was mainly in the organic matter binding state, with the smallest proportion of Cd in the exchangeable state (except for ＜0.074 mm particle size aggregates), and the proportion of Cd in the exchangeable state in the aggregates increased greatly with the increase of the depth of the profile, when the profile depth was increased to under 30 cm, the Cd in the aggregates mainly existed in carbonate bound state, and with minimal content in the residue lattice state.【Conclusion】In the typical Cd-contaminated brown calcareous soil matrices of paddy fields in the Karst area of northwestern Guangxi, the Cd is mainly enriched in aggregates of ＞2.000 mm and 1.000-2.000 mm particle size, the Cd in the aggregates of each particle size in the 0-20 cm tillage soil is mainly in the form of organic matter bound state, and with the smallest proportion in the form of exchangeable state. With the increase of the profile depth, the proportion of exchangeable Cd increases greatly, while the proportion of Cd in the stable form decreases significantly. Therefore, in the actual production process, it should focus on improving the content of large particle size soil aggregates and avoiding excessive intensive ploughing and deep tilling, reducing the exchangeable state Cd content in the ploughed soil, and ultimately reducing the risk of excessive Cd in rice during rice production. [ABSTRACT FROM AUTHOR]

【Objective】The study aimed to analyze the characteristics of cadmium (Cd) absorption and accumulation in different rice varieties under Cd polluted field in karst area of northwest Guangxi, so as to provide a reference for the safe production of rice in the region.【Method】19 rice varieties mainly cultivated in northwest Guangxi were used as test materials by the method of filed plot experiment, the production traits, yield and Cd content in different parts of rice were measured, and the characteristics of Cd enrichment and transport in different rice varieties were analyzed. After that, the low accumulation of rice varieties was recommended for the regional planting.【Result】The yield of 19 rice varieties was obviously different. Among them, the yield of Shenliangyou 9569 was 627.8 kg/667 m² significantly higher than that of other rice varieties (P<0.05, the same as below), and Yahangjinzhan had the lowest yield (429.5 kg/667 m²);The average content of Cd in different parts of rice was root>brown rice>straw>chaff. Among them the content of Cd in brown rice of Teyou 6811, H Liangyou 991 and Wushansimiao was 0.35, 0.37 and 0.37 mg/kg respectively all significantly lower than that of other varieties, and significantly reduced to 68.5%, 66.7% and 66.7% respectively when compared with the highest Cd content rice varieties Hengfengyou 777;The Cd enrichment coefficient in brown rice of Hengfengyou 777 was the highest, when Teyou 6811, H Liangyou 991, Yahangjinzhan and Wushansimiao had the lowest Cd enrichment coefficient in brown rice which significantly than the other varieties; As for the Cd transfer factor (TF) of different parts of rice, the transfer factor of root-to-straw was the lowest, and the transfer factor of chaff-to-brown rice was the highest (except for Xiangyou 1126), the transfer factor of chaff-to-brown rice of Teyou 6811, H Liangyou 991 and Wushansilmiao were significantly lower than those of other varieties. The TF of chaff-to-brown rice of Teyou 6811, H Liangyou 991 and Wushansilmiao were significantly lower than those of other varieties. Correlation analysis showed that content of Cd in brown rice was significantly positively correlated with Cd content in root, and extremely significant correlation (P<0.01) with the TF of chaff-to-brown rice and the Cd enrichment coefficient in brown rice.【Conclusion】The Cd content, Cd enrichment coefficient in brown rice and TF of chaff-to-brown rice of Teyou 6811, H Liangyou 991 and Wushansimiao were relatively low, indicating that the varieties mentioned above have the potential of low Cd accumulation. The varieties should be promoted as low Cd accumulation ones in karst area of northwest Guangxi with other remediation techniques. However, Hengfengyou 777, Yixiang 2239, Fengliangyou 3305, Xiangyou 1126, F You 498 and Guang 8 Youhuazhan account have a higher content of Cd in brown rice, therefor, they should not be recommended to be planted in the polluted fields with soil Cd content greater than 1.12 mg/kg in karst area of northwest Guangxi. [ABSTRACT FROM AUTHOR]