| The contaminated area of heavy metal has expanded each year in China. In order to define the value of biochar for controlling contaminated soil of cadmium, physical, chemical properties and cadmium adsorption-desorption kinetics behavior of biochar were researched for base, difference of rice straw direct crushing and charring into paddy soil of cadmium were compared, influence of cadmium combined forms and their relationship of biochar combined with soil were investigated, effect of physiological, biochemical traits and cadmium absorption, distribution, transport and accumulation of rice under cadmium stress with different biochar application were analysed, and variation of different returning to field measures on the quality of rice and cadmium content of brown rice were also studied. Be hope to provide a theoretical basis for cutting the cadmium residues in agricultural products, repairing paddy soil with heavy metal cadmium contaminated, preventing the spread of polluted area. The main results are as follow:1. The chemical properties analysis of different HTT biochar showed that the production rate of biochar was reduced from60%to34%, ash content was increased from12%to33%, volatile down to a quarter of rice husk, pH value was increased rapidly before HTT reaching400℃. When the HTT reached500℃, the CEC and BET surface area were increased significantly; amplification of T-500compared with the raw materials reached41%and85%. Biochar’s micro surface structure appeared clearly, ruly and porous structure was increased. Influence of physical and chemical properties in biochar was contributed to increase its adsorption properties.2. The kinetic fitting model suitable for biochar was built according maximum adsorption, solid retention capacity on balance and correlation analysis between physical and chemical properties of biochar. The main types are as follow:(1) Desorption of rice husk and biochars at three different pyrolysis temperatures were increased with the rising of initial Cd2+concentration. The adsorption effect of HTT500℃was the most, could reached99.55%in0.5mg/L Cd2+solution, and adsorption also shortened by biochar.(2) Cd2+desorption amount increased with the extension of the oscillation time, desorption of biochar at high pyrolysis temperature reached balance the fastest and was fitted with Elovich equations the best.(3) The energy spectrum analysis of biochar showed that they all had cadmium on the surface after desorbing. At the same time, the cadmium ions fixation of biochar increased with HTT.(4) Correlation analysis also showed that pH, CEC and BET surface area had a positive effect on adsorption-desorption ability of biochar.3. Analysis of cadmium combined forms in soils with different biochar treatments showed that the amount of exchangeable cadmium reduced3%,8%and11%respectively, although the other forms increased variedly. A significant negative correlation trend was showed on the linear regression analysis of physical and chemical properties with available cadmium in soil. It was found that the biochar application had a positive effect on reducing available cadmium in soil.4. Free proline and MDA content of rice flag leaf showed varying degrees of increase with the soil cadmium concentration rising. In biochar treatments, free proline content of C1and C2lower than that of CK relatively, and this effect was amplified by biochar application rate. Contents of SOD and POD down first and then increased, indicated that high biochar application ratio might cause another kind of stress and suppress the positive function on cadmium amelioration.5. The effect of cadmium accumulation was significantly in different organs of rice by biochar application. The cadmium accumulation of various organs (leaves, stems, sheath, brown rice) in different biochar application decreased by21%,19%,26%and19%compared with CK. Stepwise regression analysis of yield traits indicators and cadmium accumulation in brown rice showed that the biochar could affect the storage of the rice grain for reducing cadmium accumulation of brown rice.6. Cadmium content of brown rice with two ways of returning,(rice straw charring and crushing directly to field) had reduced significantly. The reductions were56-60%or52-57%for rice straw charring and crushing directly to field. The reduction of cadmium content in brown rice by straw charring to field was better than straw crushing directly to field.In summary, biochar could not only reduce the cadmium accumulation of brown rice by controlling the transport of cadmium, but also decreased cadmium content by increasing the storage of the rice grain. Therefore, it is a win-win measure to managing the heavy metal pollution of soil management and carbon sequestration. |
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