Effects Of Biochar/Biochar-based Fertilizer On Cd Accumulation And Transport In Rice Under Incorporation Of Astragalus Sinicus

Heavy metal pollution in paddy fields has become one of the major problems threatening food security in China.Particularly,because of the acidic soil in southern paddy fields,it leads to high biological effectiveness of heavy metals on soil,which are easily absorbed by rice.Astragalus sinicus is a major green manure crop for rice cultivation in southern,which plays an essential role in fertilizer reduction and synergism and high-yielding rice.The application of biochar and biochar-based fertilizer is one of the key tools for the current remediation of heavy metal-contaminated paddy fields.In this paper,under the conditions of Astragalus sinicus application(0.08 kg·pot^-1)in a pot experiment,different biochar dosing rates(25 g-pot^-1,50 g-pot^-1,100 g-pot^-1)and different biochar-based fertilizer dosing rates（10%biochar-based fertilizer,20%biochar-based fertilizer,30%biochar-based fertilizer,40%biochar-based fertilizer）were set and expressed as CK（control）,C25,C50,C100 and B10,B20,B30,B40,respectively.to study its effects on the growth and development of rice and the accumulation and translocation of heavy metals in various organs of rice,and to analyse its mechanism of remediation on soil heavy metal pollution through the characterization of biochar and biochar-based fertilizer.The following conclusions were drawn.（1）Effects of biochar on Cd accumulation and transport in rice under incorporation of Astragalus sinicusApplication of biochar improved rice seed yield compared to no biochar addition,with significant increases of 52.5%and 33.7%at 25 g·pot^-1and 50 g·pot^-1of biochar addition,respectively.And the application of biochar reduced the Cd content in rice seeds by 13.2%,14.1%and 11.0%in C25,C50 and C100 treatments,respectively,compared to CK.Biochar inhibited the translocation of Cd in all organs of rice,and the translocation coefficients of all translocation processes were reduced.Compared with CK,the reduction in TF_{above-ground parts/root}ranged from 5%to 11.6%,TF_straw/rootranged from 1.5%to 10.4%,and TF_seed/strawranged from 6.1%to 12.1%.（2）Effects of biochar-based fertilizer on Cd accumulation and transport in rice under incorporation of Astragalus sinicusThe addition of a certain quantity of biochar-based fertilizer to Astragalus sinicus application conditions substantially increased its rice yield compared to the CK group,while the changes in both showed a positive correlation.Both applications of biochar-based fertilizer and chemical fertilizer were able to reduce Cd content in rice hulls and brown rice,and the greatest reduction of Cd content in brown rice was observed when30%of N fertilizer application was replaced,with a 29.2%reduction compared to CK.The application of a certain level of biochar-based fertilizer significantly weakened the translocation capacity of Cd from rice roots to other organs above ground,and its translocation factor was reduced 29.2%compared to CK when biochar-based fertilizer replaced 30%N fertilizer,while the corresponding translocation factor TF _{brown rice/husk} was the lowest.（3）The characterization of biochar and biochar-based fertilizer revealed that both biochar and biochar-based fertilizer have porous structures and a large number of functional groups were found on the surface of both in the IR analysis,which may be the main reason for their passivation of Cd in soil and inhibition of Cd uptake by rice.