Remediating flooding paddy soils with schwertmannite greatly reduced arsenic accumulation in rice (Oryza sativa L.) but did not decrease the utilization efficiency of P fertilizer

Planting rice (Oryza sativa L.) in As-contaminated paddy soils can lead to accumulation of arsenic (As) in rice grains, while the application of phosphorus (P) fertilizers during rice growth may aggravate the accumulation effect. However, remediating flooding As-contaminated paddy soils with conventional Fe(III) oxides/hydroxides can hardly achieve the goals of effectively reducing grain As and maintaining the utilization efficiency of phosphate (Pi) fertilizers simultaneously. In the present study, schwertmannite was proposed to remediate flooding As-contaminated paddy soil because of its strong sorption capacity for soil As, and its effect on the utilization efficiency of Pi fertilizer was investigated. Results of a pot experiment showed that Pi fertilization along with schwertmannite amendment was effective to reduce the mobility of As in the contaminated paddy soil and meanwhile increase soil P availability. The schwertmannite amendment along with Pi fertilization reduced the content of P in Fe plaque on rice roots, compared with the corresponding amount of Pi fertilizer alone, which can be attributed to the change in mineral composition of Fe plaque mainly induced by schwertmannite amendment. Such reduction in P retention on Fe plaque was beneficial for improving the utilization efficiency of Pi fertilizer. In particular, amending flooding As-contaminated paddy soil with schwertmannite and Pi fertilizer together has reduced the content of As in rice grains from 1.06 to 1.47 mg/kg to only 0.38-0.63 mg/kg and significantly increased the shoot biomass of rice plants. Therefore, using schwertmannite to remediate flooding As-contaminated paddy soils can achieve the dual goals of effectively reducing grain As and maintaining the utilization efficiency of P fertilizers.

Automated summary

Planting rice in As-contaminated paddy soils can lead to As accumulation in rice grains, which can be aggravated by P fertilizers. However, remediation using Fe(III) oxides/hydroxides cannot effectively reduce grain As and maintain P fertilizer utilization simultaneously. In this study, schwertmannite was proposed as a remedy for flooding As-contaminated paddy soil due to its strong sorption capacity for As and its positive effect on P fertilizer utilization. The results showed that the application of schwertmannite along with P fertilization effectively reduced As mobility in the contaminated soil and increased soil P availability. Moreover, it reduced P content in Fe plaque on rice roots, benefiting P fertilizer utilization. The amendment of schwertmannite and P fertilizer together significantly reduced As content in rice grains and increased rice shoot biomass, achieving the dual goals of reducing grain As and maintaining P fertilizer utilization efficiency.