| Through field experiments,the absorption and accumulation of Cd by calcium-based soil conditioners T1,T2 and T3 in the whole growth period of rice were studied,and the effects of different calcium-based conditioners on the absorption and transport of Cd in the soil-rice system and the formation of iron film on the root surface of rice were analyzed in five typical growth stages of rice(tillering stage,jointing stage,ear pumping stage,filling stage and maturity stage),and the key period of hindering and controlling the accumulation of Cd in rice was analyzed.According to the remediation of Cd pollution in paddy fields and the Cd reduction effect of brown rice,the best conditioner with the best effect was selected based on ecological and economic benefit analysis,which provided a basis for the remediation of Cd polluted farmland and the Cd reduction of brown rice.The main findings are as follows:(1)Application of calcium-based soil conditioners significantly increased the soil pH and decreased the DTPA-Cd content at different growth stages of rice in all treatments.Among them,the T3 treatment had the greatest impact on soil pH and the best effect on Cd reduction,The DTPA-Cd content of treatment effectiveness being T1>T2>T3.The pH values of all treatments showed a consistent pattern of change during different growth stages,with the order of pH values being maturity stage>filling stage>jointing stage>tillering stage>heading stage,while the DTPA-Cd content showed the opposite pattern of change.All treatments promoted the transformation of Cd from weakly acidic extraction and reducible forms to oxidizable and residual forms in the soil.The transformation rate in the T3 treatment was higher than that in T1 and T2,and the proportion of residual Cd was highest at the maturity stage.(2)Application of calcium based conditioner significantly increased plant height,fresh weight of aboveground and fresh weight of underground(P<0.05),and the plant sizes were T3>T2>T1.However,it had no significant effect on tillering number,panicle length,panicle number,grain number per panicle,1000-grain weight and yield,and the yield of each treatment showed the order of T3>T2>T1.Calcium based conditioner T3 had a better effect on rice growth and yield.(3)After the application of calcium-based soil conditioner,the contents of DCBFe and DCB-Mn in the rice root surface were significantly increased,promoting the formation of iron-manganese plaque,with the best effect observed in the T3 treatment.The changes in the DCB-Fe and DCB-Mn contents among the treatments showed a consistent trend across different growth stages,with the highest values observed at the maturity stage,followed by the tillering,filling,jointing,and heading stages.The application of all treatments significantly promoted the adsorption of Cd by the ironmanganese plaque on the rice root surface,with the strongest effect observed in the T3 treatment.The highest amount of Cd adsorbed onto the iron-manganese plaque was observed at the maturity stage,followed by the tillering stage.The changes in the DCB-Cd content among the treatments showed a consistent trend with those of the DCB-Fe and DCB-Mn contents across different growth stages.(4)Application of calcium-based soil conditioner significantly reduced the Cd content in the roots,stems,leaves,and brown rice of rice at different growth stages.The Cd content in rice parts showed the following trend: T1>T2>T3,with T3 being the most effective in reducing Cd in brown rice.The Cd content in all treatments was below 0.2 mg/kg,which meets the national food safety standard(GB2762-2017).The Cd content in roots,stems,and leaves showed a consistent pattern: mature stage>filling stage>tillering stage>jointing stage>booting stage.(5)The concentration and transport coefficients of Cd were decreased by all treatments,and the concentration and transport of Cd were in the order of T1>T2>T3.The effect of T3 treatment on Cd enrichment and transport of brown rice was better than that of T1 and T2.The Cd enrichment and transport coefficient of each growth stage showed as follows: mature stage > filling stage > tillering stage > jointing stage > heading stage,the Cd accumulation of rice was in late growth stage > early >middle stage,the Cd enrichment ability of different rice parts was root > iron film >stem > leaf > brown rice.The transport coefficient of Cd from the iron membrane on the root surface to the root was the largest,indicating that the root system was the key part to prevent Cd from entering the stem and leaves,and the best time to control the transport of Cd from each part of rice to brown rice was from filling to maturity.(6)From the perspective of ecological benefits,the effects of soil Cd pollution remediation and preventing Cd uptake and transport in rice were as follows:T3>T2>T1.From an economic perspective,The yield increase rate,output value and net income of all treatments were T3>T2>T1.Based on the overall consideration of ecological and economic benefits,T3 showed the best performance. |
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