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Measuring and modelling the transport and root uptake of chemicals in the unsaturated zone

机译：测量和模拟不饱和区中化学物质的迁移和根吸收

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To determine the mechanisms prescribing the movement and uptake of chemicals in the soil of the rootzone, controlled experiments were carried out in four lysimeters growing tomatoes. Each lysimeter had a depth-wise array of 9 Time Domain Reflectometry (TDR) probes to monitor the soil's water content. Chloride was used as an inert tracer, and was applied with the nutrient solution used for irrigation. Sulphate was used as a reactive tracer, and was applied as a pulse resident in the upper 100 mm of the soil. The measured water contents and the concentrations of the chemicals in the soil profile at the end of the experiment were compared to a deterministic model based on Richards' equation and the convection–dispersion equation linked with various macroscopic sink terms for root water and chemical uptake. The uptake function based on matric pressure head seems to describe the uptake of water and chemicals of our tomato plants best. At high soil solution concentration chloride and sulphate exclusion occurred. Our simple model could be used to describe the major features of coupled water and chemical uptake. However, our approach of inverse modelling to infer the parameters for solute transport and root uptake could not be used to distinguish between soil-based mechanisms and plant uptake mechanisms. The choice of the root water uptake model had only a small effect on the final water content profiles, but led to differences in the final solute profiles of sulphur and chloride. This indicates that tracers might provide improved determination of the uptake mechanisms.
机译：为了确定规定根部区域土壤中化学物质移动和吸收的机制，我们在种植了4个蒸渗仪的番茄中进行了对照实验。每个测渗仪具有9个时域反射仪（TDR）探针的深度阵列，以监控土壤中的水分含量。氯化物用作惰性示踪剂，并与用于灌溉的营养液一起使用。硫酸盐用作反应性示踪剂，并作为驻留在土壤上部100 mm的脉冲施用。在实验结束时，将测得的水含量和土壤剖面中化学物质的浓度与基于Richards方程和对流扩散方程的确定性模型进行比较，该方程与根部水分和化学物质吸收的各种宏观汇项相关联。基于母体压头的吸收功能似乎可以最好地描述我们番茄植物对水和化学物质的吸收。在高土壤溶液浓度下，发生氯化物和硫酸盐排斥。我们的简单模型可以用来描述水和化学物质吸收的主要特征。但是，我们用于推断溶质运移和根系吸收参数的逆模型方法不能用于区分基于土壤的机制和植物吸收机制。根系吸水模型的选择仅对最终的水分含量分布影响很小，但导致最终的硫和氯化物溶质分布存在差异。这表明示踪剂可能会改善对摄取机制的确定。

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