基于离子活度的水培生菜营养液调控方法研究

Control System of Nutrient Solution for Hydroponic Lettuce Based on Ion Activity

摘要:

营养液动态调控是无土栽培系统重要环节，监测回用溶液的营养状况，确保将养分有效地补充到最佳浓度，以实现循环利用并降低经济成本至关重要，但营养液组分在线检测较为困难。本研究提出了一种基于pH值、电导率（Electrical conductivity, EC）、NO3-和NH4+离子活度的其他主要离子软测量方法，并设计了相应的软硬件调控平台。首先，水培生菜全周期采用园试通用配方，依据离子活度和EC贡献率计算公式，研究营养液组分的变化规律。结果表明，离子活度对营养液EC的影响具有可叠加性以及离子EC贡献率具有相对稳定的特性；随后，利用支持向量机回归算法（Support vector regression，SVR) 和遗传算法（Genetic algorithm，GA)分别建立Ca2+、Mg2+、K+离子活度回归模型，模型最优决定系数与均方根误差分别为0.9651、0.9724、0.9540和0.0146、0.0262、0.1437mmol/L；其次，设计该配方下的多离子浓度调控策略；最后，搭建软硬件调控平台，实现水肥状态检测和肥液补充。验证试验显示，定植后0~10d养分吸收量较少，均为补液后第5天执行调控指令；定植后10~30d养分吸收速率迅速增加，依据吸收量明显增加的钾、氮元素进行调控；至收获期养分总吸收量虽然增加，但吸收速率显著下降，依据吸收速率相对最快的钙元素进行调控。结果表明，本研究将固定配方的营养液EC控制水平提高到离子浓度控制水平，为满足作物生产对营养液离子浓度的动态需求提供理论依据。

Abstract:

Dynamic regulation of nutrient solution is an important part of soilless cultivation systems. Monitoring the nutritional status of reused solutions to ensure effective supplementation of nutrients to the optimal concentration is crucial for achieving recycling and reducing economic costs. However, online detection of nutrient solution components is challenging. A soft sensing method for other major ions was proposed based on pH, EC, nitrate and ammonium ion activities, and corresponding control software and hardware systems were designed. Firstly, the entire cycle of hydroponic lettuce was conducted by using a universal formula for horticultural experiment. Based on the calculation formulas for ion activity and EC contribution rate, the variation patterns of nutrient solution components were studied. The results showed that the effect of ion activity on nutrient solution EC was stackable and the contribution rate of ion EC was relatively stable. Support vector regression (SVR) and genetic algorithms (GA) were used to establish Ca2+, Mg2+, and K+ion activity regression models. The optimal determination coefficient and root mean square error of the models were 0.9651, 0.9724, 0.9540, and 0.0146mmol/L, 0.0262mmol/L, 0.1437mmol/L. Secondly, a multi ion concentration control strategy for the universal formula of garden trial leafy vegetables was designed. Finally, a control system for hardware and software was established to achieve detection and supplementation of water and fertilizer status. The validation experiment showed that the nutrient absorption was relatively small in the 0~10 days after transplanting, and the control instruction was executed on the 5th day after adding liquid;the nutrient absorption rate was increased rapidly in the 10~30 days after transplanting, and the control was carried out based on the increase of potassium and nitrogen elements that were obviously absorbed;in the harvest period, the total nutrient absorption was increased, but the absorption rate was decreased significantly, and the control was carried out based on the calcium element that had the fastest relative absorption rate. The results showed that the research improved the EC control level of nutrient solution to the level of ion concentration control, providing theoretical basis for meeting the dynamic nutrient solution ion concentration requirements of crop production.