番茄茎秆水分边缘场效应介电传感方法研究

Crop water status detecting is an important foundation for water-saving irrigation scheduling and management. In the system of crop water transport, stem on one hand is the path linking the roots to the leaves and on the other hand serves as a reservoir. To date a technical breakthrough for sensing stem water content on crop has not been made because the sensor does not allow to be inserted into the small stem; otherwise it brings physical damage to the living tissues. This study aims to establish a non-invasive method for sensing stem water content in tomato by inner-fringing field dielectric sensing method based on a ring electrode structure. The primary research contents include: (i) obtain the wide-band dielectric characteristics of tomato stem by means of simulation methods and experimental measurements and hereby optimize the operating frequency and electrode geometry; (ii) study the measuring performance of the proposed inner-fringing field dielectric sensor to determine the sensing volume and the sap flow dependence of it; (iii) comprehensively interpret the stem water content sensor signal in aid of sap flow rate and stem diameter variations under different soil water status and micro-climate conditions. The achievements of the proposed study will contribute in providing a crucial method for sensing stem water content.

作物水分信息获取是节水灌溉决策和管理的重要基础。茎秆在作物水分运移体系中既是连通根系水和冠层水的通道，又兼具水分存储的功能。由于作物茎杆无法承受嵌入传感器带来的细胞组织伤害，目前作物茎秆水分测量面临着无创检测的技术瓶颈。本研究拟以番茄为研究对象，提出利用环形电极内边缘场测量茎秆水分。重点开展以下工作：（1）以双环结构为探测电极，在较宽频率范围内通过仿真分析和实验测量两种途径研究双环电极内边缘场下番茄茎秆的介电特性，据此优化传感器测量频率和电极结构；（2）研究内边缘场茎秆水分介电传感器测量特性，分析确定内边缘场传感器水分检测范围和茎流流速、茎液离子浓度对茎秆水分测量的影响；（3）在不同土壤水分状况和微气象因子条件下，结合茎流速率和茎秆直径变化，对茎秆水分传感器信号进行解译。项目实施后将为作物茎秆水分信息获取提供关键的测量方法。

多孔介质水分测量问题是近几十年来的研究热点，特别在土壤水分测量领域许多新型传感技术和传感器不断涌现。目前市场上采用时域反射法或时域传输发等时域测量方法和频域反射法等频域测量技术的土壤水分传感器，在农业、环境监测、气象等领域获得了广泛的应用。然而在植物茎秆水分测量方面，相关的水分检测技术亟待发展。本研究根据介电测量原理并结合热脉冲测量技术，将植物水分静态含量和动态流速测量两种功能复合在微型探针上。在探针上测得的阻抗数据和温度变化曲线通过传感器上集成的计算单元反演出含水量和茎流速率。试验结果表明该传感器在水分测量上的预测精度为1.2%（体积含水率），而水流速率在10 cm/h以内绝对误差小于1 cm/h。应用该传感器将对理解植物在不同气象、水盐胁迫等条件下水分存贮和运移机制提供设备支持。