Department of Plant and Soil Science, University of Delaware, Newark, DE, USA.
Environ Geochem Health. 2024 Jul 29;46(9):339. doi: 10.1007/s10653-024-02116-x.
Irrigation management controls biogeochemical cycles in rice production. Under flooded paddy conditions, arsenic becomes plant-available as iron-reducing conditions ensue, while oxic conditions lead to increased plant availability of Cd in acidic soils. Because Cd enters rice through Mn transporters, we hypothesized that irrigation resulting in intermediate redox could simultaneously limit both As and Cd in rice grain due to As retention in soil and Mn competition for Cd uptake. In a 2 year field study, we used 6 irrigation managements that varied in extent and frequency of inundation, and we observed strong effects of irrigation management on porewater chemistry, soil redox potentials, plant As and Cd concentrations, plant nutrient concentrations, and methane emissions. Plant As decreased with drier irrigation management, but in the grain this effect was stronger for organic As than for inorganic As. Grain organic As, but not inorganic As, was strongly and positively correlated with cumulative methane emissions. Conversely, plant Cd increased under more aerobic irrigation management and grain Cd was negatively correlated with porewater Mn. A hazard index approach showed that in the tested soil with low levels of As and Cd (5.4 and 0.072 mg/kg, respectively), irrigation management could not simultaneously decrease grain As and Cd. Many soil properties, such as reducible As, available Cd, soil pH, available S, and soil organic matter should be considered when attempting to optimize irrigation management when the goal is decreasing the risk of As and Cd in rice grain.
灌溉管理控制着水稻生产中的生物地球化学循环。在淹水的稻田条件下，随着铁还原条件的出现，砷变得对植物有效，而在酸性土壤中，好氧条件会导致 Cd 对植物的有效性增加。由于 Cd 通过 Mn 转运蛋白进入水稻，我们假设导致中间氧化还原的灌溉可能会由于 As 在土壤中的保留和 Mn 对 Cd 吸收的竞争，同时限制水稻籽粒中的 As 和 Cd。在一项为期 2 年的田间研究中，我们使用了 6 种不同程度和频率的灌溉管理方法，观察到灌溉管理对孔隙水化学、土壤氧化还原电位、植物 As 和 Cd 浓度、植物养分浓度和甲烷排放有强烈影响。随着灌溉管理的干燥，植物 As 减少，但在籽粒中，有机 As 的效果强于无机 As。籽粒中的有机 As，但不是无机 As，与累积甲烷排放呈强烈正相关。相反，在更有氧的灌溉管理下，植物 Cd 增加，而籽粒 Cd 与孔隙水 Mn 呈负相关。危害指数方法表明，在所测试的土壤中，As 和 Cd 的含量较低（分别为 5.4 和 0.072mg/kg），灌溉管理不能同时降低稻谷中的 As 和 Cd。当目标是降低稻米中 As 和 Cd 的风险时，应考虑许多土壤特性，如可还原 As、有效 Cd、土壤 pH 值、有效 S 和土壤有机质，以尝试优化灌溉管理。
