[Mechanism and Effects of Soil Immobilization-foliar Inhibition Systems on Alleviating Cd in Accumulation Wheat...

In order to explore effective pathways for reducing Cd accumulation in wheat grains from Cd-contaminated farmland， a pot experiment was conducted in calcareous soil contaminated by long-term sewage irrigation to explore the mechanism and effects of the systems of soil immobilization-foliar inhibition on Cd transport and accumulation in soil-wheat plants. The systems of T1-T9 were composed of three types of soil passivators （apricot kernel biochar， agricultural and forestry waste biochar， and agricultural and forestry waste + steel slag biochar） and three types of foliar inhibitors （EDTA-Zn， Vitality 18 with amino acid， and Si-containing foliar fertilizer）. The results showed that T1， T3， T2， T4， and T8 significantly reduced Cd concentrations in wheat grains following the decreasing trend， and T1， T2， T4， T8， T3， and T7 likewise notably alleviated Cd accumulation in the grains according to the rank of decrease， whereas T5， T6， and T9 did not significantly impact grain-Cd and Cd accumulation in grain compared with that in CK. Meanwhile， the system of apricot kernel biochar and EDTA-Zn （T1） reduced the concentration and accumulation of Cd in wheat grains maximally， with reductions of 51.06% and 51.79%， respectively. Additionally， the mechanism of T1 alleviating Cd accumulation in wheat grains was clarified. The application of apricot kernel biochar （BC1） resulted in a significantly positive correlation between the proportion of changeable Cd （F1-Cd） and the relative abundance of RB41 （belonging to Acidobacteria） and negative relationship between the F1-Cd proportion and the relative abundance of Sphingomonas （belonging to Proteobacteria） in the rhizosphere soil. Furthermore， BC1 addition dramatically decreased the relative abundance of genus RB41 by 47.01% and increased the relative abundance of genus Sphingomonas by 10.71%， which increased soil pH and reduced the proportion of F1-Cd by 14.17% and accordingly enlarged the proportions of carbonate-bound Cd and iron-manganese-bound Cd by 10.41% and 11.00%， respectively. Additionally， T1 decreased root-Cd and Cd bio-accumulation factor of roots by 52.04% and 49.99%， respectively. Foliar application of EDTA-Zn during the grain-filling stage significantly reduced the Cd translocation factor from stem-leaf to rachis （at maturity） and from glume to grain （during grain-filling stage） by 45.45% and 31.29%， respectively. Finally， T1 significantly alleviated grain-Cd and Cd accumulation in wheat grains. In summary， the better pathway for effectively reducing Cd accumulation in wheat grains consists of applying apricot kernel biochar before sowing and foliar spraying of EDTA-Zn during the grain-filling stage in moderate Cd-contaminated farmland. These findings provide an effective and technical pathway for ensuring wheat grain safety production and guaranteeing safety utilization of Cd-contaminated agricultural land in the calcareous soil of North China.