不同管理措施对土壤-水稻系统中镉积累转化的影响

Effects of different management practices on cadmium accumulation and transformation in soil-rice system

  • 摘要: 针对南方酸性红壤区稻田镉(Cd)污染问题,本研究以湖南省衡阳市某典型镉污染稻作区为对象,综合评估了清洁水灌溉(T1)、沉降截源(T2)、秸秆还田(T3)、秸秆离田(T4)、施用石灰(T5)等5种措施对土壤-水稻系统中镉积累与转化的影响。5年的田间定位试验发现:试验区大气沉降镉通量呈现出明显的月动态差异,干湿沉降是主要的沉降途径,月均值为0.15 mg·m−2,夏半年镉沉降通量较冬半年高3 ~ 5倍,2017—2019年镉通量年均降幅达21.6%;石灰处理土壤pH由5.47提升至6.26,有利于镉向残渣态的转化,残渣态占比由17%升至35%,镉活性降低,累积降低根系镉含量78.8%,籽粒镉含量60.0% ~ 80.0%,显著减少水稻植株中镉的富集,降幅达46.3% ~ 80.0%;清洁水灌溉和秸秆离田分别使表层土壤总镉含量较初始值(0.41 mg·kg−1)下降12.1%和10.5%,而秸秆还田组上升9.3%;秸秆离田能有效减少茎和籽粒中镉的积累,并使根系镉含量降低43.0%;大气沉降截源可显著降低镉在水稻地上部位的富集量,秸秆还田会导致镉从根部向地上部迁移,增加了镉在根和茎的富集。大气沉降过程可能是镉污染区土壤和水稻中镉的重要来源,镉污染区农田施用石灰、净化灌溉水等是农田土壤安全利用的技术措施。

     

    Abstract: Aiming at the problem of cadmium (Cd) pollution in paddy fields in the acidic red soil region of southern China, this study took a typical cadmium-contaminated rice-growing area in Hengyang City, Hunan Province as the object, and comprehensively evaluated the effects of five measures, including clean water irrigation (T1), sedimentation and source interception (T2), straw returning (T3), straw removal (T4), and lime application (T5) on the accumulation and transformation of Cd in the soil-rice system. The five-year field experiment shows that the atmospheric deposition flux of cadmium in the experimental area exhibits obvious monthly dynamic differences. Dry and wet deposition is the main way of deposition, with a monthly average of 0.15 mg·m−2. The cadmium deposition flux in summer half year is 3 ~ 5 times higher than that in winter half year, and the annual average decrease of cadmium flux from 2017 to 2019 is 21.6%. Lime treatment increases soil pH from 5.47 to 6.26, facilitating the transformation of cadmium to residual state. Lime treatment increases the proportion of residual state from 17% to 35%, decreases cadmium activity with 78.8% reduction of cadmium content in roots and 60.0% - 80.0% reduction in grains; which significantly reduces the enrichment of cadmium in rice plants by 46.3% - 80.0%. Compared with the initial value (0.41 mg·kg−1), the total cadmium content in the surface soil is decreased by 12.1% and 10.5% under clean water irrigation and straw removal, respectively; while the straw returning group is increased by 9.3%. Straw removal from the field could effectively reduce the accumulation of cadmium in stems and grains with 43.0% reduction of cadmium content in roots. Atmospheric deposition could significantly reduce the accumulation of cadmium in the aboveground part of rice. Straw returning could lead to the migration of cadmium from root to aboveground part, and increase the accumulation of cadmium in root and stem. The atmospheric deposition process may be an important source of cadmium in soil and rice in cadmium-contaminated areas. The applications of lime and purification of irrigation water in farmland in cadmium-contaminated areas are the technical practices for the safe use of farmland soil.

     

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