[Synergistic Repair Effect of Calcite-Based Passivator and Low-Accumulation Maize].

In this study, a field experiment of soil passivation and low accumulation-crops was carried out for typical northern alkaline cadmium and lead compound-polluted farmland soil. Calcite was used as the main passivation material, and a small amount of slaked lime, zeolite powder, and biochar were combined to form a group passivation agent. The effects of passivators on soil physicochemical properties, bioavailability of the heavy metals Cd and Pb, and the yield and plant (stalk and seed) content of heavy metals Cd and Pb in low-accumulation maize were investigated under different grouping conditions of calcite+slaked lime (CL), calcite+zeolite (CZ), calcite+biochar (CB), and calcite+slaked lime+zeolite+biochar (CLZB). The results showed that:① all applications of passivating agent ensured the normal growth of maize and slightly increased the 1000 grain weight and maize yield. ② The effects of different calcite-based passivators on soil physical and chemical properties were different. The CL, CZ, CB, and CLZB treatments increased soil pH by 0.46, 0.25, 0.12, and 0.13 units, respectively, but had no significant correlation with soil fertility index (P>0.05). ③ DTPA leaching and ion exchange state contents of Cd and Pb in soil could be significantly reduced by different calcite-based combinations with passivators, and the reduction rates of Cd and Pb in DTPA leaching were 49.36% and 72.55%, respectively. The reduction rates of ion exchange Cd and Pb contents were 55.39% and 78.52%, respectively. ④ The contents of Cd and Pb in stems, leaves, and grains of low-accumulation maize were further reduced by different passivating agents. The contents of Cd and Pb in the stems and leaves of maize were reduced by 45.93% and 67.00% after CLZB treatment, and the contents of Cd and Pb in grains were decreased by 25.17% and 46.62%, respectively. Moreover, the contents of Cd and Pb in DTPA extraction and ion exchange states were significantly positively correlated with the contents of Cd and Pb in corn stems, leaves, and grains (P<0.01). The results showed that the combined use of combination passivators and low-accumulation crop varieties can obtain better restoration effects in the remediation of cadmium and lead combined-polluted farmland in the middle alkaline soil in northern China.

[Cadmium Accumulation Characteristics of Different Heat Varieties Under Cadmium Stress].

In order to provide technical support for the safe utilization of heavy metal-polluted farmland, we screened wheat varieties with a low accumulation of Cd in grain via a pot experiment. For this purpose, we respectively investigated the enrichment and transport characteristics of Cd in various plant parts of 119 wheat varieties under the conditions of 1.5 mg·kg-1 (low content) and 4.0 mg·kg-1 (high content) Cd-contaminated soil and explored the correlation between the Cd content of different organs of wheat and the relationship between Cd content in soil and the uptake of Cd by wheat. The results showed that:① there were significant differences in the ability to accumulate and transport Cd in roots, stems, leaves, and grains of tested wheat varieties (P<0.05). Under the condition of low Cd content, the Cd enrichment ability of each part of the wheat plant was as follows:leaf>stem ≈root>grain; under high-content stress conditions, the Cd enrichment ability of each part of the wheat plant was:leaf>root>stem>grain; under different content conditions, the Cd transport ability of each part of the wheat plant was:leaf>stem>grain. Cd content in the wheat shoot was positively correlated with total Cd content and ion-exchangeable Cd content in soil (P<0.01) and was closely related to strong transpiration under the pot experiment. ② The correlation coefficient r of BCFCd of wheat roots, stems, leaves, and grain was -0.267 to -0.645, showing a very significant negative correlation (P<0.01), indicating that with the increase in soil Cd content, the migration and accumulation degree of Cd in wheat plant organs showed a downward trend. Moreover, the negative correlation between BCFCd and soil Cd content in stems was significantly higher than that in roots, leaves, and grains, indicating that the enrichment of Cd in wheat plants largely depended on the accumulation and transportation of stems. ③ The correlation coefficient r of Cd content between the root and stem, root and leaf, root and grain, stem and leaf, stem and grain, and leaf and grain in low-and high-content groups was 0.450-0.763, showing a very significant positive correlation (P<0.01), indicating that there was a close transport relationship among the wheat organs, and the degree of translocation from the root to stem and stem to leaf was higher than that from the stem to grain and leaf to grain. ④ Using cluster analysis and enrichment and translocation coefficient sequencing, this study screened 16 and 11 wheat varieties with low Cd accumulation under the soil cadmium content of 1.5 mg·kg-1and 4.0 mg·kg-1, respectively. Among them, Luohan 7 could be used as the optimal wheat variety with low Cd accumulation under the conditions of low-, medium-, and high-Cd content.