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Modeling water flow and solute transport in soils under different irrigation management practices.

机译：在不同灌溉管理方式下模拟土壤中的水流和溶质运移。

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摘要

In this study, several important topics related to water flow and solute transport in soils under different irrigation conditions were studied using numerical modeling. Water flow and solute transport in irrigated soils are greatly dependent on different irrigation practices. Water flow and solute transport in soils were investigated under alternate-furrow irrigation, fixed-furrow irrigation, and the conventional every-furrow irrigation. To account for water and salt stresses to plants, a root-water uptake model was integrated into the water and solute movement model, modified CHAIN_IR, to simulate root-water uptake at various irrigation water use and salinity levels. Parameters used in the root-water uptake model were evaluated. Long-term irrigation with saline water predicted root-water uptake to be substantially reduced, even at very low irrigation application levels attributable to salt accumulation. To study the effects of spatial variability of saturated hydraulic conductivity ( Ks) on water and solute movement, two-dimensional random fields of Log Ks were generated with five different standard deviations (0.5, 0.75, 1.0, 1.25, and 1.5). Spatial variability of Ks was shown to have similar effects on mean values of water and solute leaching fractions for flood, drip, and sprinkler irrigation methods. Water movement using four root-water uptake models with different root density functions was evaluated in a loamy sand soil under furrow irrigation. Two main distributions of root systems, in cylindrical and conical shapes, were examined at two irrigation levels. The effects of random fields of Ks on these root-water uptake models were also discussed. The simulation results suggested that the shape of root systems had a greater effect on root-water uptake than the root distribution function. Numerical solutions of water flow in variably saturated porous media resulted in poor mass balance due to the inherent nonlinear characteristics of the governing equation. To improve mass balance under irrigation conditions with large outflow water flux, a hybrid method that utilized either the h-based or mixed formulations based on the local soil water condition was proposed. The h-based formulation should be adopted if the absolute change of pressure heads between time steps is smaller than 3 cm, otherwise, the mixed formulation should be applied. The hybrid method resulted in better mass balance than the mixed formation with the same tolerance levels for iterations within a time step. To achieve similar mass balance errors, the mixed formation required much more computation time than the hybrid method.
机译：在这项研究中，使用数值模型研究了与不同灌溉条件下土壤中的水流和溶质迁移相关的几个重要主题。灌溉土壤中的水流和溶质运移在很大程度上取决于不同的灌溉方式。在交替沟灌，固定沟灌和常规逐沟灌溉下研究了土壤中的水流和溶质运移。为了考虑对植物的水分和盐分胁迫，将根水吸收模型集成到水和溶质运动模型中（修改后的CHAIN_IR），以模拟各种灌溉用水和盐度水平下的根水吸收。评估了根系吸水模型中使用的参数。即使使用归因于盐分累积的非常低的灌溉水平，用盐水长期灌溉也预测根水吸收将大大减少。为了研究饱和导水率（Ks）的空间变异性对水和溶质运动的影响，生成了Log Ks的二维随机场，具有五个不同的标准差（0.5、0.75、1.0、1.25和1.5）。结果表明，对于洪水，滴灌和洒水灌溉方法，Ks的空间变异性对水和溶质淋洗分数的平均值具有相似的影响。在沟灌条件下，在壤土壤土上使用四种具有不同根系密度函数的根系吸水模型评估了水分运动。在两个灌溉水平下，检查了根系的两个主要分布，呈圆柱形和圆锥形。还讨论了钾素随机场对这些根系吸水模型的影响。模拟结果表明，根系形态对根系水分吸收的影响大于根系分布函数。由于控制方程的固有非线性特性，在可变饱和多孔介质中水流的数值解导致较差的质量平衡。为了提高灌溉条件下流出水通量大的土壤质量平衡，提出了一种混合方法，该方法基于当地土壤水条件使用基于h或混合的配方。如果各时间步之间的压头绝对变化小于3 cm，则应采用基于h的配方，否则应采用混合配方。混合方法与混合地层相比，在同一时间步长内具有相同的公差级别，因此可以实现更好的质量平衡。为了获得相似的质量平衡误差，混合形式比混合方法需要更多的计算时间。

著录项

  • 作者

    Hao, Xinmei.;

  • 作者单位

    University of Wyoming.;

  • 授予单位 University of Wyoming.;
  • 学科 Agriculture Soil Science.
  • 学位 Ph.D.
  • 年度 2004
  • 页码 133 p.
  • 总页数 133
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 土壤学;
  • 关键词

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