| In recent years,due to heavy metal pollution in soil and chemical fertilizer abuse,cadmium in rice seriously exceeded the standard,which has become a research hotspot.Studies have shown that organic fertilizer or biochar can effectively improve soil conditions,However,there are few studies on the effect of combined application of biochar and organic fertilizer on rice cultivation in heavy metal contaminated soil,Therefore,pot experiments were carried out to study the effects of biochar,organic fertilizer and their combination on Cd in different parts of rice in contaminated soil,and their effects on soil physical and chemical properties and rice yield.The following conclusions were obtained through experiments:(1)The results showed that the soil eh value of each treatment group decreased,Soil pH increased with the application of biochar,but tended to be neutral with flooding time.The content of nitrogen in paddy soil increased with the increase of biochar,Soil C/N ratio decreased with the increase of biochar.Soil available Cd decreased in different degrees in rice growth stage.(2)The content of Cd in rice plants showed the phenomenon of root>leaf>stem>brown rice.The Cd content in brown rice was reduced significantly by application of biochar(p<0.05),and with the increase of biochar addition,Cd accumulation in brown rice decreased gradually.With the addition of biochar,the grain quality of each treatment group increased significantly.The low content of biochar could promote the rice yield.(3)Different fertilization methods had a significant impact on soil properties,and the pH value of rice soil was greatly affected by oil cake organic fertilizer;high N treatment group had a more significant effect on the reduction of available Cd in soil at Rice maturity stage(p<0.05).With the application of organic fertilizer,Cd content in brown rice was significantly reduced(p<0.05).No matter what fertilization method,rice yield was increased(by grain),and the yield increased with the increase of fertilizer amount.Compared with the control,the yield of oil cake treatment groups was the most significant(p<0.05).(4)Biochar was combined with different fertilization methods,Soil pH decreased in the early stage and increased in the later stage,and Eh decreased significantly.The content of available Cd decreased gradually.Compared with the control,biochar and organic fertilizer could slightly reduce soil available Cd content with flooding time,but the difference was not significant(p<0.05).(5)The Cd content in brown rice was significantly decreased by biochar of organic fertilizer or inorganic fertilizer application(p<0.05),which was lower than the standard limit of rice Cd content in China(0.2 mg/kg).With the combination of low biochar and high vermicompost and high biochar and oil cake,the inhibition effect on Cd accumulation in brown rice was the most significant(p<0.05).The results showed that high content of organic fertilizer significantly increased rice grain quality by 137.9%and 148.1%.The rice yield was increased by 161.2%in the treatment of low content biochar combined with high content inorganic fertilizer.Combined application of high biochar and organic fertilizer(oil cake)can reduce Cd in brown rice and meet rice yield,which is a relatively ideal fertilization method for Cd contaminated soil. |
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