Wheat/oilseed rape-rice rotation is popular in paddy fields in Asia countries, especially in China. The return of the preceding crop straw can improve soil fertility and promote the growth of the later crop. Sulfur (S) is one of the essential nutrients, which can improve the yields, qualities and pathogen resistances of wheat, oilseed rape and rice plants. In general, oilseed rape from the Brassica family requires much more S than wheat or rice from the Gramineae family. Some of the paddy fields in China are polluted by cadmium (Cd) - a toxic heavy metal with high mobility. The transfer of Cd from soils to brown rice poses a threat to human health, in particular to those who use rice as the staple food. Recent studies recommended that S could be used as efficient method for controlling Cd in brown rice. However, the effects of S application on Cd accumulation in the edible parts of wheat/oilseed rape are rarely studied; in further, the residual effects of S on the later rice are still unknown for wheat/oilseed rape-rice rotation systems. For one aspect, the thesis seeks to answer the scientific question: whether the application of S in the wheat/oilseed rape season, combined with straw return, will affect the Cd concentration in the grain of the later rice. Insight with the key mechanisms such as soil Cd availability, Cd enrichment in plaque on the rice root surface, and Cd transfer in rice plants will be important to answer this question. For another aspect, the thesis will also seek to answer the technical question: whether the application of S prior to the preceding wheat/oilseed rape can reduce the concentration of Cd in the brown rice to less than the limit value (0.2 mg kg-1, GB2762-2017). Based on the investigations, the thesis has tried to figure out the best S application levels to limit Cd in the brown rice under wheat/oilseed rape-rice rotation. The following greenhouse pot experiments were performed. A pot experiment was used to simulate wheat/oilseed rape-rice rotation. Crops were grown in low Cd soils (background, 0.35 mg Cd kg-1) and high Cd soils (with the addition of 10 mg Cd kg-1, as CdCl2) supplied with four S levels (0, 30, 60, 120 mg S kg-1, as Na2SO4). We examined the effects of S application on Cd uptake by the preceding crops - wheat (HM-33) and oilseed rape (HHY-5). Then, we continued to investigate the subsequent effects and mechanisms of S application on Cd uptake by the later rice (Kitaake) in wheat/oilseed rape-rice rotation with the return of straw of the preceding crop to the soil. We got the following results for the wheat-rice rotation system. As to the preceding wheat, S application increased concentration of Cd in wheat grain irrespective of soil Cd levels (Chapter 2). For instance, wheat grain Cd concentration increased by 15%, 35%, and 160% (p＜0.05) at 30, 60, and 120 mg S kg-1 levels respectively for low Cd soils. Without Cd stress or S stress (≤ 60 mg kg-1), the reason could be that S application increased available Cd in rhizosphere soils around wheat roots and thus increased Cd uptake by wheat. Under Cd stress or S stress, the reason could be attributed to the increase of Cd transfer from wheat root to the grain. With the increase of S levels to the preceding wheat, brown rice Cd concentration peaked at 60 mg S kg-1 irrespective of soil Cd levels (Chapter 3). With application of S ≤ 60 mg kg-1 prior to the preceding wheat, Cd uptake increased by rice and thus increased the concentration of Cd in brown rice both for low and high Cd soils. At the highest S level (120 mg S kg-1), S application decreased Cd transfer from root to brown rice for low Cd soils, but the protection effects of S disappeared under Cd stress conditions. In general, S application increased Cd uptake by wheat (rice), or promoted Cd transfer from root to wheat grain (brown rice). For the oilseed rape-rice rotations system we got the following results. Irrespective of soil Cd levels, rapeseed Cd concentration and the Cd transfer factors from roots to rapeseeds peaked at 30 mg S kg-1 (Chapter 4). The results indicate that application of S at 30 mg S kg-1 may significantly stimulate the transfer of Cd in oilseed rape plants. The influence of S on rice following oilseed rape related to soil Cd levels and differed to that in wheat-rice rotation (Chapter 5). For low Cd soils, concentrations of Cd in brown rice from treatments with S addition were smaller than brown rice from the non-S addition treatment. This is because S application inhibits Cd transfer from rice root to brown rice. For high Cd soils, concentrations of Cd in brown rice peaked at 60 mg S kg-1. When the application of S ≤ 60 mg kg-1, S application significantly increased Cd uptake by rice roots but also reduced Cd transfer from root to brown rice. Finally, Cd concentrations in brown rice increased with the increasing S levels in the range of 0-60 mg S kg-1. At the highest S level (120 mg S kg-1), the concentration of Cd in brown rice remained unchanged compared with 60 mg S kg-1 treatment for high Cd soils. This is because S application not only promoted Cd uptake by the later rice but Cd solubility is relatively low under high S levels. Also, high S application tended to increase Cd transfer from the root to brown rice. Although the color of iron plaque on the rice root surface changed from red-brown to dark-brown when S application levels increased irrespective of soil Cd levels, iron plaque had little effects on Cd accumulation in brown rice. Based on the investigations the following overall conclusions and recommendations can be made. Sulfur application to wheat-rice rotation increased concentrations of Cd in wheat grain and brown rice. The concentrations of S in Cd-contaminated paddy fields are relatively high in the south of China. We recommended that we do not apply S-containing fertilizer, for instance, calcium superphosphate, for wheat-rice rotation in paddy fields. For oilseed rape-rice rotation, Cd accumulation in rapeseed was stimulated by 30 mg S kg-1; Cd accumulation in brown rice suppressed by S application for low Cd soils. Thus, we recommend to cultivate this in S-sufficient paddy fields or supply enough S fertilizers. For high Cd soils, oilseed rape could be treat as a Cd-remediation plants; the rapeseeds could be used only for industry purpose but not for food. When oilseed rape-rice rotation is cultivated in low Cd soils, concentrations of Cd in rapeseed and brown rice were relatively low, and their risks were negligible. When we compared the brown rice Cd concentration between wheat-rice rotation and oilseed rape-rice rotation at the same S and Cd levels, the differences were not significant. The largest difference appeared when S was supplied at 60 mg kg-1 to the high Cd soils, which resulted in almost double the amount of Cd in brown rice from wheat-rice rotation than brown rice from oilseed rape-rice rotation (0.23 mg kg-1 vs. 0.14 mg kg-1). The requirements on Cd concentration by the National Food Safety Standard of China are stricter than the recommendation by FAO/WHO. According to National Food Safety Standard - Maximum Levels of Contaminants in Foods (GB 2672-2017), the requirements are that wheat grain < 0.1 mg Cd kg-1, rapeseed < 0.5 mg Cd kg-1 and brown rice < 0.2 mg Cd kg-1. For low Cd soils, the Cd concentration in the edible parts from oilseed rape-rice rotation system met for the above requirements. However, Cd concentrations in wheat grain for all S application levels were higher than the above limit value even for low Cd soils. For high Cd soils, the Cd concentration threshold in brown rice at 60 mg S kg-1 could not be met for the wheat-rice rotation system. In summary, for low Cd soils, the risk of Cd in wheat grain exceeding the limit values (GB 2672-2017) was greater than that of rapeseed; however, the risk of Cd above the threshold value in later rice was low, irrespective of wheat-rice and rape-rice rotation. For high Cd soils, Cd concentrations in the edible parts of the preceding wheat and oilseed rape always exceeded the limit values, approximately by 57-78 times for wheat grains and 5.2-12 times for rapeseeds, respectively. As a result, it might be discreetly suggested to treat the preceding crop (wheat and oilseed rape) as Cd-remediation crops, and monitoring the Cd accumulation in the later rice. The wheat/oilseed rape-rice rotation systems might be a method for Cd-remediation and rice-production simultaneously.