Nanjing Agricultural University, College of Resources and Environmental Sciences, Nanjing, 210095, China.
Nanjing Agricultural University, College of Resources and Environmental Sciences, Nanjing, 210095, China.
Environ Pollut. 2020 Jun;261:114151. doi: 10.1016/j.envpol.2020.114151. Epub 2020 Feb 10.
Rice is a major dietary source of the toxic trace metal Cd. Large variation in Cd concentration in rice grain was documented by global and regional surveys, with this variation difficult to predict from soil tests. Even within individual fields, a large spatial variation is often observed but the factors controlling this within-field spatial variation are still poorly understood. In the present study, we used field- and laboratory-based experiments to investigate the effects of a gentle slope gradient within paddy fields (a common farmers' practice to facilitate water flow from the inlet to the outlet) on Cd availability and grain Cd concentrations in unlimed and limed soils. In our field experiments, a gentle slope resulted in large spatial variations in soil redox potential (Eh) and pH upon soil drainage during rice grain filling. As a result of these variations in Eh and pH, there was a 6- to 7-fold spatial within-field variation in grain Cd concentrations, which were the highest in the irrigation inlet area associated with higher Eh values and the lowest in the outlet area with lower Eh values. Our results highlight that soil Eh, and more importantly, field-moist soil pH during grain filling determine grain Cd concentration and accordingly, incorporating measurements of soil redox status (or water content) and pH of field moist soils (rather than air-dried soils) during grain filling may improve the prediction of grain Cd concentrations. Delaying drainage during grain filling or increasing soil pH by liming is effective in reducing grain Cd accumulation.
稻米是有毒微量元素镉的主要膳食来源。全球和区域调查记录了稻米中镉浓度的巨大差异，这种差异很难通过土壤测试来预测。即使在单个田块内，也经常观察到很大的空间变异性，但控制这种田间空间变异性的因素仍知之甚少。在本研究中，我们使用田间和实验室实验来研究稻田内缓坡梯度（农民为了便于水流从进水口流向出水口而采用的一种常见做法）对未施石灰和施石灰土壤中镉的有效性和稻米镉浓度的影响。在我们的田间实验中，缓坡导致在水稻灌浆期间土壤排水时土壤氧化还原电位（Eh）和 pH 值出现很大的空间变化。由于 Eh 和 pH 值的这些变化，田间粮食 Cd 浓度存在 6 到 7 倍的空间变化，在与较高 Eh 值相关的灌溉进水口区域最高，在 Eh 值较低的出水口区域最低。我们的结果表明，土壤 Eh，更重要的是，在灌浆期间田间湿润土壤的 pH 值决定了稻米的 Cd 浓度，因此，在灌浆期间纳入土壤氧化还原状态（或含水量）和田间湿润土壤 pH 值的测量（而不是风干土壤）可能会提高对粮食 Cd 浓度的预测。在灌浆期间延迟排水或通过施石灰提高土壤 pH 值可有效减少粮食 Cd 积累。
