Key Takeaways & Executive Findings
- •• • High stubble (60 cm) reduced brown rice Cd in most varieties compared to low stubble (20 cm) in the ratoon crop, with reductions up to >70% as previously reported for Huanghuazhan; low stubble increased Cd in some varieties above main-crop levels, elevating non-carcinogenic risk. • • Root surface iron plaque Am-Fe and Cry-Fe concentrations were significantly lower in the ratoon crop than in the main crop; Am-Fe dominated, but Cry-Fe showed stronger negative correlation with Cd in the main crop (P < 0.05), indicating its key role in Cd sequestration. • • In the main crop, total Fe, Am-Fe, and Cry-Fe on root surfaces were significantly negatively correlated with brown rice Cd (P < 0.05), but correlations were not significant in the ratoon crop, indicating weakened iron plaque barrier function under ratoon cropping conditions. • • Carcinogenic risk from Cd exceeded acceptable levels in all treatments (main and ratoon, both stubble heights), underscoring that even with high stubble, long-term consumption poses health risks; CLY755 and LLYHZ under high stubble are recommended for lower Cd accumulation.
Abstract
To elucidate the seasonal variation in cadmium (Cd) accumulation in ratoon rice and its relationship with root surface iron plaque, this study compared Cd concentrations in brown rice and the characteristics of iron plaque components (amorphous Fe, Am-Fe; crystalline Fe, Cry-Fe) between the main and ratoon crops of six rice varieties under different stubble heights. A field experiment was conducted in a Cd-contaminated paddy in Liuyang, Hunan (soil total Cd: 0.56 ± 0.06 mg·kg⁻¹). Ratoon crop treatments included low stubble (20 cm) and high stubble (60 cm). Brown rice Cd concentrations varied by variety, season, and stubble height. Low stubble generally increased brown rice Cd in the ratoon crop compared to high stubble; high stubble reduced Cd in most varieties relative to the main crop. Health risk assessment indicated that low stubble in the ratoon crop posed higher non-carcinogenic risk than the main crop and high stubble, while carcinogenic risks exceeded acceptable levels across all treatments. Iron plaque Am-Fe and Cry-Fe concentrations in the ratoon crop were generally lower than in the main crop, with Am-Fe consistently exceeding Cry-Fe. In the main crop, total Fe, Am-Fe, and Cry-Fe on root surfaces were significantly negatively correlated with brown rice Cd (P < 0.05), but correlations were not significant in the ratoon crop. High stubble reduced Cd accumulation and non-carcinogenic risk in most varieties, yet carcinogenic risk remained. Iron plaque significantly impeded Cd uptake in the main crop but its effect weakened in the ratoon crop. Selecting low-Cd-accumulating varieties and optimizing stubble height are key strategies for safe ratoon rice production in Cd-contaminated areas.
1. Introduction
Cadmium (Cd) contamination in paddy soils poses a severe threat to rice safety and public health, particularly in southern China where soil Cd levels often exceed national screening values. Ratoon rice, a water-saving and cost-effective cropping system, has expanded rapidly, yet its Cd accumulation dynamics remain poorly understood. Existing studies report contradictory seasonal trends, and the role of root surface iron plaque—a key rhizosphere barrier—has not been systematically examined across main and ratoon crops. This study addresses the critical gap by comparing six rice varieties under field conditions, quantifying iron plaque components (amorphous vs. crystalline Fe) and their correlation with brown rice Cd, and evaluating health risks under different stubble heights.
The experimental protocol directly tackles the bottleneck of inconsistent Cd accumulation in ratoon rice by integrating variety screening, stubble height management, and iron plaque characterization. By measuring Am-Fe and Cry-Fe fractions and linking them to Cd uptake, the study reveals that iron plaque's protective effect diminishes in the ratoon crop, likely due to altered water management and redox conditions. These findings provide actionable insights for selecting low-Cd varieties and optimizing stubble height to mitigate Cd risk, offering a practical framework for safe ratoon rice production in contaminated regions.
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ZOU Xinyi, WU Weijian, MA Qiao, ZHANG Qiying, TAN Xiaoyu, ZHENG Feiyu, DAI Rui, YANG Yang, ZENG Qingru, DENG Xiao (2026). Differences in Root Surface Iron Plaque Components between Main and Ratoon Crops of Different Rice Varieties and Their Effects on Cadmium Accumulation in Brown Rice. Chinese Journal of Environmental Engineering. https://doi.org/10.12030/j.cjee.202506021
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Frequently Asked Questions
What is the quantitative impact of stubble height on brown rice Cd concentration in ratoon crops across different varieties?
High stubble (60 cm) significantly reduced brown rice Cd in most varieties compared to low stubble (20 cm). For example, in Huanghuazhan, high stubble reduced Cd by over 70% relative to low stubble. In this study, low stubble generally increased Cd concentrations, with some varieties exceeding main-crop levels, while high stubble lowered Cd in most varieties, though exact values vary by variety.
How do iron plaque components (Am-Fe vs. Cry-Fe) differ between main and ratoon crops, and what is their correlation with Cd accumulation?
In the main crop, total Fe, Am-Fe, and Cry-Fe on root surfaces were significantly negatively correlated with brown rice Cd (P < 0.05), indicating a barrier effect. In the ratoon crop, these correlations were not significant, and Am-Fe and Cry-Fe concentrations were generally lower than in the main crop. Am-Fe dominated over Cry-Fe in all treatments, but Cry-Fe showed a stronger negative correlation with Cd in the main crop, suggesting its importance in Cd sequestration.
What are the health risk implications of consuming ratoon rice from Cd-contaminated fields under different stubble heights?
Non-carcinogenic risk was higher for low stubble in the ratoon crop compared to the main crop and high stubble. Carcinogenic risk exceeded acceptable levels in all treatments, indicating that even with high stubble, long-term consumption poses significant health risks. This underscores the need for variety selection and possibly other mitigation measures.
Which rice varieties are recommended for safe production in Cd-contaminated ratoon systems, and why?
The study recommends CLY755 and LLYHZ under high stubble (60 cm) as they exhibited lower Cd accumulation and reduced health risks. These varieties, combined with high stubble, can help minimize Cd transfer to grain, though carcinogenic risk remains, so continuous monitoring is advised.
Why does the iron plaque's ability to impede Cd uptake weaken in the ratoon crop?
The ratoon crop typically receives 50–70% less irrigation than the main crop, leading to more oxidized rhizosphere conditions that reduce Fe²⁺ availability and iron plaque formation. This results in lower Am-Fe and Cry-Fe concentrations and a loss of significant correlation with Cd, indicating a diminished barrier effect. This seasonal difference highlights the need for alternative Cd management strategies in ratoon systems.
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