Objectives Effects and key influencing factors of intercropping remediation on maize Cd concentrations in Cd-contaminated maize farmland were analyzed, in order to provide technical parameters for the farmland soil remediation during production.
Methods The data were obtained by searching from the published papers in “CNKI” and “Web of Science” database from 2006 to 2020, using “Cd contamination”, “intercropping”, “maize” etc. as the main keywords. According to the requirement of meta-analysis, there were 770 sets of data for Cd concentrations in maize from 33 literatures. The effect value of intercropping was defined as the response ratio of its intercropping over monoculture treatment within a same trial, and meta-analysis method was used to quantitatively analyze the contribution of each factor on remediation response effect.
Results Compared with monoculture maize, intercropping remediation in field could significantly reduce Cd concentration in maize grain, stem-leaves and root, especially with the highest decrease rates in grain. Centipede grass + Amaranthus paniculatus L., Centipede grass, Amaranthus paniculatus L. and Solanum nigrum significantly inhibited the concentration of Cd in maize grain. And Cd concentrations in grain of Dongdan, Haihe 28 and Lüyu 269 were decreased significantly under intercropping remediation. Weak acid or neutral soil enhanced the inhibition of intercropping remediation on Cd concentration in maize grain. In both safe utilization and strict control farmland, Cd concentration in maize grain was significantly reduced with intercropping remediation. Row spacing with 0–30 cm significantly reduce Cd concentration in roots, but row spacing had no effects in grain and stem-leaves. However, meta-analysis showed that intercropping remediation had no significant effect on the reduction of Cd concentration in maize, for there were many intercropping plants and maize varieties in intercropping remediation under pot culture conditions. In addition, the effects of intercropping plants such as corngrass, ryegrass and alfalfa, as well as the main crop Jinzhumi, were different in field or pot trails.
Conclusions Intercropping remediation can significantly inhibit the concentration of Cd in maize and improve the remediation efficiency of Cd-contaminated maize farmland. The selection of suitable maize cultivars and intercropping remediation plants has a significant impact on improving the effect of intercropping remediation. At the same time, the row spacing of maize and intercropping plants, soil pH and Cd concentration before remediation also have a certain impact on the remediation effect of intercropping. The results provide some technical parameters and theoretical basis for the remediation technology of Cd contaminated corn in China.
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