Effects Of Different Amendments On Cadmium Activity And Cadmium Accumulation In Wheat In Calcareous Chao Soil

In recent years,the problem of heavy metal pollution in farmland soil is becoming more and more serious.Although the environmental capacity of heavy metal in alkaline soil is often higher than that of acidic soil,the Cd content of wheat grains in the northern calcareous soil still exceeds the national safety standard.The heavy metal Cd will not only affect the quality of wheat,but also enter the human body through the food chain and damage human function.The effects of different amendments on Cd activity in calcareous chao soil and Cd accumulation in wheat were systematically studied in this paper,explore the use of different amendments after soil-wheat system migration of heavy metals Cd transport,bioavailability of heavy metal Cd in soil,soil p H,the content of Cd in wheat grains,materials characterization.The suitable passivation materials were screened for field.(1)Although the physical and chemical properties of soil in field and pot experiments were different,the application of sepiolite,Si-Ca-Mg fertilizer,hydroxyapatite,lime,Ca-Mg-P fertilizer and two kinds of biochar materials could increase the soil p H value and facilitate the stabilization of soil Cd.The application of superphosphate,chicken manure and modified humic acid all reduced the soil p H value,which was not conducive to the stabilization of soil Cd activity.(2)The amendments have different properties,but it can reduce the content of DTPA-Cd and the activity of heavy metal Cd in soil.In general,the treatment effect of Si-Ca-Mg fertilizer is the best.The speciation analysis showed that the exchangeable and carbonate-bound Cd with higher activity in the soil were transformed into Fe-Mn ferric oxide,organically bound and residual Cd with lower activity,which greatly reduced the mobility of Cd in the soil.(3)According to the screening test of remediation and improvement materials for Cd contaminated soil in pot culture,Si-Ca-Mg fertilizer has a good inhibiting effect on Cd absorption and transport in various organs of wheat plant.Compared with the control,the content of Cd in roots,stems and leaves,glumes,grains decreased by71.49%,61.26%,86.44% and 90.87%,respectively,in wheat mature stage under the treatment of 1.2% Si-Ca-Mg fertilizer,which indicated that Si-Ca-Mg fertilizer had certain application value in remediation of heavy metal Cd pollution in calcareous soil.(4)The results of SEM-EDS showed that Si-Ca-Mg fertilizer,Ca-Mg-P fertilizer,hydroxyapatite and two kinds of biochar improved materials mostly contain C,O,Si,Ca,Al and other elements.The surface characteristics of each material are different.The Si-Ca-Mg fertilizer is ridge-shaped and the surface is smooth.The surface of the two biochar materials is rough and uneven,which is helpful for the adsorption and complexation fixation of Cd.(5)The effect of different amendments and their recombination on soil Cd activity and wheat absorption of Cd,Cu and Zn showed that,different amendments can reduce the contents of Cd,Zn and Cu in wheat grains.Meanwhile,the Cd/Zn ratio and Cd/Cu ratio in wheat grains can be significantly reduced by Si-Ca-Mg fertilizer,thus improving the edible safety of wheat more effectively.All these indicate that the application of Si-Ca-Mg fertilizer can effectively reduce the concentration of Cd in wheat grains.(6)Field experiment shows that Si-Ca-Mg fertilizer had a good passivation effect on heavy metals Cd,Cu and Zn in soil.The Cd content of the local wheat variety(Zhengmai-369)reached the national food safety standard by 0.5% treatment of Si-CaMg fertilizer.The application of Si-Ca-Mg fertilizer could reduce the Cu content in various organs of wheat plant,but had no significant effect on the Zn content in wheat grain.(7)The content of Cd in the grain of wheat variety Pingan-11 could still reach the national safety index without Si-Ca-Mg fertilizer,but the yield was reduced compared with that of local wheat to a certain degree.Compared with the local wheat varieties,Zhoumai-369 has a certain effect of increasing yield.The Cd content in grain can reach the national food safety level after 0.5% Si-Ca-Mg fertilizer treatment.The results showed that Si-Ca-Mg fertilizer had certain application value in remediation of heavy metal Cd pollution in calcareous aquic soil.Therefore,in practical application,the wheat variety Zhoumai-36 can be applied with Si-Ca-Mg fertilizer to achieve good economic effectiveness.