Numerical analysis of sensor-based flood-floor ebb-and-flow subirrigation system with saline water

Ebb-and-flow is a well-known and common greenhouse irrigation system. In this paper, a specific numerical model for a sensor-based flood-floor ebb-and-flow irrigation system has been developed using one-dimensional Richards’ equation for water flow and two-site sorption advection-dispersion model for simulation of solute transport. The model was validated against analytical and numerical results proposed in the literature, and acceptable agreement was obtained in all cases. Maximum RMSE (MAE) was 0.053 m (0.273 m) for water flow and 0.021 (0.065) for solute transport. The model was then used for a parametric study of how different factors (such as salinity of irrigation water, triggering and cutoff thresholds, sensor position and flooding depth) would affect transpiration of sensor-equipped solitary pot under ebb-and-flow irrigation system for two different crops. It was revealed that sensor position and water salinity were significantly influential on transpiration of the pots. Finally, the synchronized sensor equipped-sensorless module of the numerical model was used to optimize the flood-floor ebb-and-flow irrigation system considering different factors using Taguchi approach. It was concluded that installing a water content sensor, whose triggering and cutoff thresholds were at −10 and −2 m, at the upper-half of the center-positioned pot would result in higher transpiration and lower unevenness of water distribution.

潮汐式灌溉（Ebb-and-flow）是一类广为人知且应用普遍的温室灌溉系统。本文基于一维水流理查兹方程（Richards’ equation）与溶质运移模拟双位点吸附对流弥散模型，构建了针对传感器调控型床面潮汐式灌溉系统的专用数值模型。通过与文献中已发表的解析解与数值解对比验证该模型，所有工况下均取得了可接受的拟合精度。水流模拟的最大均方根误差（RMSE，Root Mean Square Error）与平均绝对误差（MAE，Mean Absolute Error）分别为0.053 m与0.273 m，溶质运移模拟的对应值则为0.021与0.065。
随后，利用该模型开展参数敏感性分析，探究不同影响因素——包括灌溉水盐度、触发与截止阈值、传感器安装位置以及淹灌深度——对两种作物在潮汐式灌溉系统下配备传感器的单株盆栽蒸腾速率的影响。研究结果表明，传感器安装位置与水盐度对盆栽蒸腾速率具有显著影响。
最后，本研究采用数值模型的集成同步传感器的无传感器模块，结合田口方法（Taguchi approach）对多因素影响下的床面潮汐式灌溉系统进行优化。最终得出结论：在居中放置盆栽的上半区域安装含水率传感器，且将其触发阈值与截止阈值分别设为-10 m与-2 m时，可获得更高的蒸腾速率与更均匀的水分分布。