Effect Of Biochar On Growth Of Rice And Cadmium Forms In Cadmium-contaminated Soil

Soil is the basic environmental element that constitutes the ecosystem,and it is an important material basis for human survival and development.With the advancement of industrialization and urbanization,the problem of heavy metal pollution in China is becoming more and more serious,which has attracted the attention of people from all walks of life.Biochar is a kind of carbon-rich solid material,which is the product of animal and plant residues under the condition of limited oxygen and at low temperature?350-700°C?.Due to its porous,abundant functional groups,large specific surface area and high CEC characteristics,it can be used to repair heavy metal pollution in soil,thereby reducing the toxicity and effectiveness of soil heavy metals,and reducing their mobility.In this paper,corn cob biochar?CCB?and industrial biochar?GB?were used as remediation agents.The effects of CCB on the growth of rice in contaminated soil were studied by pot experiment.Through the soil indoor culture experiment,we studied the solid holding capacity of raw industrial biochar?GB?and phosphate modified industrial biochar?P-GB?on soil cadmium.This study provides a new theoretical and experimental basis for the application of biochar in the field of soil restoration.The main research contents and results are as follows:1.Effect of corn cob biochar on rice growth and cadmium uptake in cadmium-contaminated soilUsing CCB as experimental material and rice as indicator plant,pot experiment was conducted to study the effects of CCB on contaminated soil pH,available Cd,rice yield,rice biomass and Cd content of edible parts of rice.The results showed that:?1?Adding CCB could improve the soil pH,and the soil pH increased by 0.14,0.25 and 0.26,respectively,when the addition amount was 1%,3%and 5%,respectively,and all treatments reached a significant level.?2?The addition of CCB could reduce the content of available Cd in the soil,and its decline of the effective Cd content increased with the increase of the amount of CCB.When the addition amount was 5%,the decrease was 18.2%.?3?Applying CCB to cadmium-contaminated soil could significantly improve the growth indexs,such as panicle length,number of tillers per plant,panicle number,plant height,and 1000-grain weight.Compared with the control,these indicators increased by 10.92%,20.88%,12.78%,12.02%and 43.52%,respectively.?4?The addition of CCB in cadmium-contaminated soil could obviously promote the growth of above-ground and below-ground rice.The more the amount added,the more obvious the effect.?5?The addition of CCB significantly decreased the content of Cd in edible parts of rice.Compared with the control experiment,Cd content in edible parts of rice decreased by 37.6%,48.5%and 35.6%,respectively,when the addition amount was 1%,3%and 5%.2.Effect of industrial biochar and Its calcium phosphate modification on cadmium forms in soilThe industrial biochar produced by a company was used as raw material,modified biochar?P-GB?was prepared by the equal volume impregnation method of calcium phosphate solution.Through indoor incubation experiments,this experiment explored the effect of modified biochar?P-GB?and original industrial biochar?GB?on cadmium forms in soil,and combined with elemental analysis,N₂ adsorption-stripping experiment?BET?,Fourier transform infrared spectroscopy?FTIR?,X-ray diffraction?XRD?,Cold field emission scanning electron microscope?FESEM?and BCR extraction analysis experimental characterization.The mechanism of cadmium passivation by biochar was initially discussed.The results showed that:?1?GB's pH=9.76,P-GB's pH=10.10,P-GB's pH was 0.34 higher than GB,with stronger alkalinity;After modification,the ash content of biochar increased by16.9%,higher aromatic and less polarity.?2?GB and P-GB contained a large number of oxygen-containing surface functional groups,such as-OH,-COOH,C-O-C,and-OCH₃,which were aromatic.The total pore volume and pore size of modified biochar were increased.?3?Compared with control treatment?CK?,GB and P-GB treatments significantly increased the soil pH value after 30 days of culture,and the pH increased from 7.64 to 8.43 and 8.52,respectively,and the effect of pH increase positively related to the biochar applied;The pH of90 d in soil culture was similar to that of 30 d,indicating that the soil with biochar has a higher pH buffer capacity.?4?After 30 days and 90 days of cultivation,all treatments significantly reduced the content of available cadmium in the soil.Among them,the effect of adding 5%of P-GB was better,and the passivation effect of P-GB on cadmium is better than GB.?5?Compared with CK,the application of different amounts?1%,3%,5%?of GB and P-GB reduced the content of cadmium in the acid extracted form of the soil,which increased the content of reducible cadmium and residual cadmium in the soil.The results showed that the two kinds of biochar had passivation effect on cadmium in soil,and the treatment effect of3%of P-GB was better.