Effects Of Different Modifiers On Cadmium Contaminated Soil And Chinese Cabbage Growth

With the rapid development of society,the pollution of heavy metals in soil is becoming more and more serious.Chinese cabbage is an indispensable vegetable in people’s daily life.Cadmium in the soil can enter the human body through the food chain and endanger human health.How to effectively repair heavy metal contaminated soil and reduce the absorption of Cd by vegetables has become a hot issue that needs to be solved urgently.The application of modifiers is a feasible method for remediation of heavy metal contaminated soil,and has broad application prospects in the control and remediation of heavy metal pollution in soil.This article studies the basic properties of peat,modified peat,and biochar,and uses the three materials as modifiers.The amount of modifier is set according to the equivalent carbon amount,a total of 10 treatments were set up,CK,without adding modifier;P1-P3,adding 1%,2.5%,5%peat respectively;MP1-MP3,adding 1%,2.5%,5%modification peat respectively;BC1-BC3,adding 1.5%,3.8%,7.5%biochar respectively.Through pot experiment of Chinese cabbage in greenhouse,the effects of different modifiers on soil physical and chemical properties,enzyme activities,chemical fraction of Cd,and the effects of modifiers on the growth and quality of Chinese cabbage were studied.The main results are as follows:(1)The sample peat is an acidic(pH=4.5)herbal peat,with a loose and porous structure.After modification,the porous characteristic become more significant,and has a smoother surface texture.The carbon layer structure of biochar is compact and porous.Modified peat has the largest cation exchange capacity,which is 27.17 cmol·kg-1,followed by biochar.The pore diameter of peat is large,but the specific surface area and pore volume are small.After modification,the specific surface area,pore volume and average pore diameter of peat have increased.The three modifiers are mainly mesoporous materials.(2)The application of modifiers can improve the physical and chemical properties of the soil.Peat can significantly reduce the soil pH,while modified peat and biochar can increase the soil pH.Peat can significantly increase the soil EC.The P3 treatment can increase the soil cation exchange capacity by 25.2%.(3)Application of modifiers alleviates the inhibition of soil enzyme activity by cadmium,and the soil urease activity increased with the increase of the amount of modifier applied.The P3 and MP3 treatment can significantly increase urease activity by 76.3%and 70.6%.Modified peat has the best effect on improving the activity of soil catalase.Applying different amounts of modified peat can significantly increase the activity of catalase,which increased by 9.2%,14.3%and 18.4%.The application of low amount of biochar can significantly increase the activity of soil catalase,but increasing the application amount,the activity of catalase decreased instead.Different treatments of peat could significantly increase soil invertase activity,which increased by 61.3%,74.9%and 70.9%respectively.Modified peat and biochar had no significant effect on soil invertase activity.With the increase of application amount,the soil invertase activity in the biochar treatment showed an increasing trend and then decreased.(4)The application of modifier has no significant effect on soil cadmium content.The externally added cadmium makes the cadmium mainly in the state of weak acid extraction and has strong activity.The P3 treatment increased the cadmium content of weak acid-extractable fractions in the soil by 5.6%,the application of modified peat and biochar can effectively reduce the weak acid-extractable fractions of Cd.The MP3 treatment has the best effect,with a decrease of 24.2%.Cadmium in soil changes to stable,low activity fractions.All treatments with the modifiers can increase the residual cadmium content in the soil.(5)The application of modifiers can promote the growth of Chinese cabbage,and with the increase of the application amount,the dry weight of the shoots showed an upward trend.The treatments with high application amount can significantly increase the dry weight of the shoots,and the application of peat and modified peat is better than biochar in increasing production.Application of modifiers can also alleviate the toxic effects of cadmium and improve the quality of Chinese cabbage.Peat,modified peat and biochar can significantly increase the chlorophyll content at the maximum application amount.The soluble sugar content increased with the increase of the amount of the modifier.The BC2 and BC3 treatment can significantly increase the soluble sugar content of Chinese cabbage,with an increase of 37.5%and 38.9%respectively.(6)The content of Cd in the shoots of Chinese cabbage is less than that in the root.The application of modified peat and biochar can significantly reduce the Cd content in the shoots of Chinese cabbage,and with the increase of the application amount,the Cd content of the plants showed a downward trend.The MP2 and MP3 treatments significantly reduced the Cd content in the roots of Chinese cabbage.The MP3 treatment can effectively reduce the transfer and accumulation of cadmium in the soil to the shoots,and the enrichment coefficient is significantly reduced by 21.3%.