蚯蚓粪对镉在土壤-水稻系统中迁移转化影响

Effects of vermicompost on the migration and transformation of heavy metal cadmium in soil-rice systems

为降低稻米中镉(Cd)含量,探究了牛粪源蚯蚓粪对水稻不同时期Cd吸收积累的影响。选取中性水稻土,采用盆栽试验,对牛粪源蚯蚓粪添加下水稻生长过程中土壤氧化还原电位(Eh)、pH和土壤Cd形态的变化规律及水稻重金属Cd积累量进行测定分析。结果表明:相较于对照(不添加蚯蚓粪),施加蚯蚓粪使水稻土壤Eh显著降低,显著降低水稻分蘖期土壤pH值,进入抽穗扬花期后无显著影响;蚯蚓粪的添加改变了土壤Cd的赋存形态,在分蘖期除低添加量6.3 g C·kg-1土外均显著降低环境活性态Cd含量,且添加量越大降幅越大,在水稻抽穗扬花期仅高添加量41.3 g C·kg-1土有显著降低效果,在完熟期各处理组均显著降低其含量;施加蚯蚓粪能显著降低水稻糙米中Cd的含量,蚯蚓粪施用量6.3 g C·kg-1土下糙米Cd含量降低48.08%,施用量达16.3 g C·kg-1土时糙米Cd含量降至0.157 mg·kg-1,符合国家稻米Cd控制标准,继续增加施用量后糙米Cd含量无显著差异。对于水稻植株,蚯蚓粪在41.3 g C·kg-1土下可显著降低全生育期各部位Cd含量,除抽穗扬花期茎部无明显规律外,其余各时期水稻根、茎及叶Cd含量均表现为蚯蚓粪添加量越大降低效果越明显。研究表明,蚯蚓粪在全生育期可通过降低土壤Eh影响土壤可交换态Cd含量从而降低水稻对Cd的吸收量。

To reduce Cd content in rice and to explore the effect of vermicompost(CV)on Cd absorption and accumulation in different crops of rice, a pot experiment was carried out to investigate the effects of CV on soil Eh value, pH value, fractionation of Cd in paddy soils,and Cd content in rice grains. The results show that CV can significantly reduce the Eh value of paddy soil. Moreover, it considerably reduced the pH of paddy soil at the tillering stage of rice. However, it had no significant effect after the crop entered the heading stage. The addition of CV changed the fraction of Cd in the crop. In the tillering stage, the environmentally active Cd content decreased significantly,except for the low addition of 6.3 g C·kg-1 soil. The larger the amount of CV added, the greater the decrease of Cd. In the heading stage of rice, an added CV of 41.3 g C·kg-1 soil had a significant reduction effect, and in the ripening stage, the content of Cd in each treatment group decreased drastically. The addition of CV significantly reduced the content of Cd in brown rice. The content of Cd in brown rice decreased by 48.08% when CV of 6.3 g C·kg-1 soil was added. When the amount of CV was increased to 16.3 g C·kg-1 soil, the Cd content of brown rice decreased to 0.157 mg·kg-1, meeting the national rice Cd control standard of less than 0.2 mg·kg-1. There was no significant difference in the content of Cd in brown rice among the groups with the increase in the amount of CV. The content of Cd in all parts of the rice plant decreased significantly in the whole growth period in 41.3 g C·kg-1 soil. While the Cd content showed no obvious pattern in the stem of the rice plant in the heading stage, the content of Cd in the roots, stems, and leaves of rice in other growth periods showed that the greater the amount of CV, the more obvious the effect. During the whole growth period, CV reduced the content of exchangeable Cd in the soil by decreasing the soil Eh, consequently reducing the amount of Cd absorbed by rice.