| Cadmium(Cd)contamination is a relatively common type of heavy metal contamination in agricultural fields at present.The development of rice yield and quality in China is largely constrained by heavy metals,and straw return is an effective agronomic measure that can regulate heavy metal pollution of agricultural products.Therefore,it is important to study the low cost,effective,high-yielding and Cd-reducing straw return method to improve the safe use of straw in Cd-contaminated farmland and to ensure food security production in China.we investigated the effects of straw biochar return(BR),straw return(SR),straw burned return(SBR)and straw removal(CK)in double-season rice fields under different Cd levels of stress with different Cd concentrations(0 mg/kg,1 mg/kg and 5 mg/kg,denoted by Cd0,Cd1 and Cd5,respectively).on soil Cd morphology,rice growth,the accumulation and distribution characteristics of heavy metals in the plants of double-season rice fields.The main findings were as follows:(1)Compared with CK,straw return and straw burned return significantly increased the number of grains per spike and yield in the early rice season in all three Cd concentrations,with increases ranging from 13.4-14.6% and 12.9%-17.8% for straw return and 11.8%-13.4% and 11.7%-13.2% for straw burne return,respectively.There was no significant difference in yield among four treatments in late rice season.Moreover,the yield and above ground biomass showed a decreasing trend with increasing Cd concentration in all treatments except straw return,which the aboveground biomass of straw return treatment were significantly higher than Cd0 concentration under Cd1 concentration.(2)Compared with CK,straw return and straw burned return significantly reduced Cd content in all parts of early and late rice plants at both Cd1 and Cd5 contamination levels,meanwhile reducing the Cd content of fine rice to below the standard limit value(0.200 mg/kg)at Cd1 contamination level.Straw biochar return significantly reduced early rice plant Cd content under Cd1 treatment and late rice plant Cd content under Cd1 and Cd5.The Cd content of all parts of rice plant increased with the increase of exogenous Cd concentration.The transfer and partition coefficients of cadmium in the stem were the highest for all treatments.(3)Compared with CK,straw biochar return significantly increased soil fast-acting potassium content and was significantly higher than other straw return methods at Cd1 and Cd5 concentrations,straw return significantly increased fast-acting potassium and effective phosphorus content,and straw burned return significantly increased early rice soil soluble organic carbon(DOC)content,which was significantly higher than other straw return methods.In addition,all three straw return methods significantly increased soil pH and organic matter content at all Cd concentrations.Overall,all of them achieved the purpose of soil acid control and fertilization.(4)Compared with CK,straw return significantly reduced the soil effective state Cd content in both early and late rice at Cd1 and Cd5 concentration,while straw burned return only reduced the effective state Cd content at Cd1 concentration in early and late rice,and straw biochar return only reduced the effective state Cd content at Cd1 concentration in late rice.The conversion of Cd from the reducible and oxidizable states to the residual state was promoted by different straw return methods at Cd5 concentration.Overall,combining yield characteristics and soil Cd uptake,the straw return treatment not only reduced the soil effective Cd content and Cd content in all parts of the rice plant,but also effectively increased the number of spikelets per spike and yield in early rice,with the best effect in Cd1 concentration;straw charred return in late rice significantly reduced the Cd content of the rice plant and the soil effective Cd content in Cd1 concentration. |
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