小麦秸秆生物质炭对旱地土壤铅镉有效性及小麦、玉米吸收的影响

Effects of biochar on Cd Pb availability and uptake by maize and wheat in upland soil

采用高(40 t·hm^(-2))、低(20 t·hm^(-2))两个不同施用量将小麦秸秆生物质炭施用到小麦-玉米轮作模式下的碱性旱地土壤,分析生物质炭对Pb、Cd污染土壤中小麦、玉米籽粒Pb、Cd的富集以及土壤Pb、Cd的生物有效性的影响。结果表明:旱地土壤中,小麦秸秆生物质炭在小麦、玉米两季均能有效提高土壤有机碳含量,两季最高增加量分别是对照的2.4倍和2.8倍;同时显著降低土壤Ca Cl2-Pb和Ca Cl2-Cd的含量,最大降幅分别达到53%和50%,进一步表现为小麦籽粒Pb、Cd含量的显著降低,降幅最高分别为43%和21%,但小麦籽粒Pb、Cd含量仍高于现行国家标准(Cd<0.1 mg·kg^(-1),Pb<0.2 mg·kg^(-1)),而对玉米籽粒Pb、Cd含量无显著影响。在对污染水平及施炭量的多因素方差分析中发现,20 t·hm^(-2)的施炭量可在短期内达到修复目的,而40 t·hm^(-2)施炭量的治理效果可至少维持两个生长季。因此,小麦秸秆生物质炭对碱性旱地土壤Pb、Cd污染的修复,主要是通过提高土壤有机碳含量以及生物质炭丰富的官能团对土壤Pb、Cd的吸附螯合及络合作用来降低土壤Pb、Cd的生物有效性,从而降低小麦籽粒的Pb、Cd富集,并且其持效性在一定生物质炭施用范围内随施用量的增加而延长。

A field study was conducted by applying wheat straw biochar with the high（40 t·hm-2）and low（20 t·hm-2）application rates in a wheat-maize rotation upland field. The indicators related to heavy metal pollution, including the available concentrations of Pb, Cd in soil and the uptake amount in grain of wheat and maize, were determined and analyzed after two growing seasons. The results showed that, compared to no biochar amendment, wheat straw biochar application significantly increased soil organic matter（SOM）by 2.4 and 2.8 times. The highest decrease rates of available Cd, Pb being 53% and 50% were observed in the form of Ca Cl2-Cd and Ca Cl2-Pb, respectively. The concentrations of Pb and Cd in wheat grain were also significantly reduced, and the decrease rates were as high as 43% and 21% respectively.However, the Pb and Cd concentrations in wheat grain were still higher than the current national standard. No obvious change of Pb and Cd concentration was observed in maize grain. A multivariate analysis indicated that biochar had significant remediation effect on upland heavy metal pollution with the application level of 20 t·hm-2in short term, while a long term effect（two growing seasons at least）was found under the application level of 40 t·hm-2. The further analysis implied that wheat straw biochar may significantly reduce the bio-available heavy metal in upland soil by adsorbing heavy metal with chelation and complexation effects dominated by biochar sourced functional groups, and the remediation effect can be last longer with the increase of application level in a certain range.