Influence Of Swine Manure-derived Biochar On Cd Availability And Uptake By Rice In Acidic And Alkaline Paddy Soils

Cadmium（Cd）is one of the most serious environmental problems in agricultural soils in China,particularly in pa ddy soils.In recent years,biochar,derived from the pyrolysis of biomass feedstocks in the lab-scale have shown to have potential to improve Cd remediation in soils,because of its highly porous structure,active functional groups and generally high p H.There is limited information on the pilot-scale conversion of animal amnures to biochar,and the effects of biochar on the availability and Cd uptake in plant in the field experiment.In this study,heavy metal-loaded swine manure were selected as the feedstock for preparing biochar at a range of temperatures and Cd-contaminated paddy soils were treated with these biochars.The objectives of this study are to:（1）determine and compare the chemical fractionation and bioavailability of heavy metals,and assess the phytotoxic effect of heavy metals in the resulting biochars;（2）compare the effects of swine manure and its biochar applied at different rates on the availability and uptake of Cd in rice plant in acidic and alkaline paddy field soils;（3）investigate the continuous application rate of biochar on the uptake of Cd and nutrient in rice grains.Main results are summarized as follows:（1）Biochars derived from the pyrolysis of composted swine manure,were characterized and the effects of pyrolysis temperature on availability of heavy metals were investigated.Results showed that the pilot-scale pyrolysis process converted the exchangeable heavy metals to a relatively stable fraction,and significantly decreased the available heavy metals in swine manure-derived biochar.The pyrolysis process thus reduced the potential ecological risk of the treated swine manure by reducing the release of heavy metals contained in the biochar.GI values indicated that biochars produced from pilot-scale pyrolysis process had no phytotoxicity,while biochars produced from lab-scale pyrolysis exhibited a moderate phytotoxicity.（2）The addition of swine manure and its biochar in an acidic paddy soil significantly increased the p H,and decreased the concentrations of Ca Cl₂-extractable Cd.Cd in the acid-soluble fraction was decreased in the soil amended with biochar while it increased in the residual and reducible fractions.The concentrations of Cd in rice shoots,roots,husks and grains significantly decreased with the increasing ratios of biochars.The concentration of Cd in rice grain was treated with 5%bochar lower than the guideline limit of 0.2 mg kg^-1 for Cd.（3）There was no significant diference on the p H in an alkaline soil amended with swine manure-biochar.Biochar applied at high rates of 5%significantly decrease the Ca Cl₂-extractable Cd in soil at the rice tillering stage.The treatment of swine manure-biochar can directly transform the acid-soluble fraction of Cd to r esidual Cd fraction in soils.Compared with the treatment of raw swine manure,the application of biochar can decrease the accumulation of Cd in rice grains.（4）In the second year,the continuous addition of swine manure-biochar significant decreased the availability and uptake of Cd in rice in acidic paddy soils.However,there was no significant diference on the p H and available Cd in the alkaline soil.Compared with the addition rates of biochar,the addition rate of 5%once before rice planting showed a stable passivation effect on soil available Cd,and decreased the accumulation of Cd in rice grains.However,there was no significant difference on uptake of mineral elements in rice grains.