School of Civil & Environmental Engineering, Cornell University, Ithaca, NY, USA.
Department of Earth and Atmospheric Sciences, SUNY-Oneonta, Oneonta, NY, USA.
Environ Geochem Health. 2023 Nov;45(11):8135-8151. doi: 10.1007/s10653-023-01702-9. Epub 2023 Aug 7.
Rice is a global dietary staple and its traditional cultivation under flooded soil conditions leads to accumulation of arsenic (As) in rice grains. Alternate wetting and drying (AWD) is a widely advocated water management practice to achieve lower As concentrations in rice, water savings, and decreased methane emissions. It is not yet clear whether AWD leads to tradeoffs between concentrations of As and micronutrient elements (e.g., zinc, manganese, molybdenum) in rice grain. We analyzed pore water chemistry and rice grain composition data from a field experiment conducted in Arkansas, USA, in 2017 and 2018 to test the hypothesis that AWD will have diverging effects on oxyanion-forming (arsenic, molybdenum) vs. cationic (cadmium, zinc, manganese, copper) trace elements. This was hypothesized to occur via decreases in soil pH and/or precipitation of iron oxide minerals during oxidizing conditions under AWD. Solubility of all trace elements, except zinc, increased in more reducing conditions. Consistent with our hypothesis, AWD tended to increase grain concentrations of cationic elements while decreasing grain concentrations of oxyanionic elements. Decreases in total As in rice grains under AWD were mainly driven by changes in dimethylarsinic concentrations, with negligible changes in inorganic As. Linear mixed-effects modeling showed that effects of AWD on grain composition were more significant in 2017 compared to 2018. These differences may be related to the timing of dry-downs in the developmental stage of rice plants, with dry-downs during the heading stage of rice development leading to larger impacts on grain composition of certain elements. We also observed significant interannual variability in grain elemental composition from continuously-flooded fields and postulate the warmer temperatures in 2018 may have played a role in these differences.
水稻是全球主要的粮食作物，其传统淹水种植方式导致稻谷中砷（As）的积累。干湿交替灌溉（AWD）是一种广泛提倡的节水灌溉管理方法，可以降低稻米中砷的浓度、减少甲烷排放。然而，目前尚不清楚干湿交替灌溉是否会导致稻米中砷和微量元素（如锌、锰、钼）浓度之间的权衡。我们分析了 2017 年和 2018 年在美国阿肯色州进行的田间试验中的孔隙水化学和稻米成分数据，以检验干湿交替灌溉对形成阴离子（砷、钼）和阳离子（镉、锌、锰、铜）痕量元素的影响是否不同的假设。这是因为在 AWD 条件下的氧化条件下，土壤 pH 值降低和/或氧化铁矿物沉淀。除锌外，所有痕量元素的溶解度在更还原的条件下增加。与我们的假设一致，AWD 倾向于增加谷物中阳离子元素的浓度，同时降低谷物中阴离子元素的浓度。AWD 下稻米总砷含量的降低主要是由于二甲基砷酸浓度的变化，而无机砷的变化可以忽略不计。线性混合效应模型表明，与 2018 年相比，AWD 对谷物成分的影响在 2017 年更为显著。这些差异可能与水稻生长发育阶段的干燥时间有关，在水稻生长的抽穗期进行干燥处理会对某些元素的谷物成分产生更大的影响。我们还观察到连续淹水农田的谷物元素组成存在显著的年际变化，并假设 2018 年较高的温度可能在这些差异中发挥了作用。
