基于FDR原理的土壤氮含量检测方法的研究

设计一款基于土壤介电理论中的频域反射法(Frequency Domain Reflectometry)的土壤氮含量传感器，提供了一种用于土壤中氮含量的快速测定的新方法。试验装置以2个金属平行板为敏感元件、含氮土壤为电介质，设计试验在不同土壤含水率梯度下，探索土壤含氮量对土壤介电特性的影响，用平行板电极借助磁场来检测土壤中氮含量，建立传感器的输出频率和土壤质量含水率和氮含量的数学模型。试验结果表明，在土壤含水量一致的情况下，传感器的输出频率随着氮素含量的增加呈递减趋势。模型调整R2达到0.97，验证了模型的有效性。在前人研究的基础上，基于已经成熟的驻波比法(Standing Wave Ratio，SWR)土壤水分传感器间接测量含氮土壤的介电常数，使用烘干法得到土壤的容重，即可得到含氮土壤较为精确的含水量，通过建立的模型根据传感器输出频率与含水量得到土壤的氮含量。

Detection Method of Soil Nitrogen Content Based on FDR Theory

The study aims to design a soil nitrogen content sensor based on Frequency Domain Reflectometry, which is one of the theories of soil dielectrics, to provide a novel method for rapid determination of nitrogen content in soil. With two parallel plates as sensitive element, nitrogen soil as dielectric, the experiments were designed to explore the impact of nitrogen content on the dielectric properties of the soil under different soil moisture gradient in the experimental device, and with the aid of the magnetic field effect parallel plate electrodes to detect the nitrogen content in the soil and build the relationship model of the sensor output frequency and soil mass water content and soil nitrogen content. The results indicated that when the soil water content was the same, the output frequency of the sensor with the nitrogen content decreased progressively. The adjust R2 of the model was 0.97 which could demonstrate the validity of the model proposed. On the basis of previous research, by using sophisticated soil moisture sensor based on Standing Wave Ratio, the dielectric content of nitrogen of soil could be indirectly obtained and the soil bulk density could be gained by the drying method, so as to know the accurate moisture content of soil that contained nitrogen, therefore, the soil nitrogen content could be calculated through the model according to the output frequency of the sensor and soil water content.