| With the rapid development of intensive and large-scale livestock and poultry breeding industry in China,the numbers of farms are gradually increasing,and a large number of livestock and poultry manure is also produced.Due to the use of various feed additives containing heavy metal elements,a large number of heavy metals such as Cu,Zn,Cr and Pb are discharged into the environment with livestock manure,endangering human health.Composting is one of the main ways of recycling livestock and poultry waste,while traditional composting has the disadvantages of over standard heavy metal content and low maturity.The results show that adding biochar in composting can passivate the heavy metals in livestock manure and improve the quality of composting.Therefore,this experiment is to study the effects of biochar on the basic physical and chemical properties of compost,the content of heavy metals and their morphological changes,and the growth of soil and vegetables in the process of composting.This study provides a reference for the application of biochar in deer manure and straw compost.In this experiment,deer manure and straw were used as composting raw materials,and the proportion of biochar added was 0%,2.5%,5.0%,7.5% and 10.0%(dry basis).There were five groups of experiments(CK,BC1,BC2,BC3 and BC4 treatment groups in turn).The five groups of composting were started at the same time with the carbon nitrogen ratio(C / N)of30 and the water content is 60%.The physical and chemical properties,the content and morphology of heavy metals in the composting process were studied.BC2 treatment group had the longest duration of high temperature,which was 13 days.BC3 treatment group had the highest urease activity.After composting,with the increase of the proportion of biochar added,the water content gradually decreased and the degradation rate of OM gradually increased,which indicated that the addition of biochar promoted the water holding and water holding function and humification process of the reactor.The trend of pH change in each group was similar.But the pH peak value of the treatment group with biochar was higher than that of the CK treatment group.From the maturity point of view,after composting,the C /N ratio of CK group was 22.18,and the C/N ratio of the treatment group with biochar decreased to below 20,which was much higher than that of CK treatment group.The GI of CK treatment group was 81.00%,and that of BC2 treatment group was 98.40%.The compost maturity of BC3 group was better than that of CK group.At the end of composting,due to the decline of the quality of the compost,the heavy metalsshowed a relative concentration effect.The contents of Cu,Zn,Cr and Pb in all treatment groups were higher than those before composting,and the growth rate is 11.07-33.13%.BC4 treatment group has the best passivation effect on Cu and Zn.BC3 treatment group has the best passivation effect on Cr,and BC2 treatment group has the best passivation effect on Pb.The results of redundancy analysis showed that the correlation between the shape change of heavy metal Cu and the physical and chemical properties was the highest(96.23%),followed by Zn(89.11%),Pb(83.54%)and Cr(76.49%).The results of pot experiment showed that the application of compost can significantly improve the yield,chlorophyll content and nitrogen content of pakchoi,and reduce the nitrate content in Pakchoi,and the higher the proportion of biochar,the better the effect.The application of compost has no significant effect on the phosphorus content of pakchoi,and the potassium content of Pakchoi increases with the proportion of biochar.In all experimental groups,the content of heavy metals in the blank treatment group was the lowest,and the content of heavy metals in the biochar treatment group was lower than that in the CK treatment group,and the difference was significant.The BC4 treatment group had the best effect on the decrease of Cu(71.50%)and Pb(75.86%)bioavailability,the BC2 treatment group had the best effect on the decrease of Zn(69.92%)bioavailability,the BC3 treatment group had the best effect on the decrease of Cr(47.62%)bioavailability.After the application of compost,the soil pH of the blank group and the compost group increased by 0.11-0.63.However,the EC of soil decreased to a certain extent,with a decrease of 12.50-36.59%.At the end of pot experiment,the decrease of soil OM was 4.55%-8.68%.With the increase of the proportion of biochar,the degradation rate of OM increases gradually.The content of TN,TP and TK decreased to some extent.The bioavailability of heavy metals Cu and Pb increased during compost application,which had the risk of being reactivated.The results of principal component analysis and comprehensive score showed that adding 2.5%biochar was the best way to improve soil quality. |
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