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Recalling existing research, it can be found that a great deal of research has been conducted on the generalized electromagnetic measurement of soil in the past and abroad, and remarkable progress has been made. However, the existing methods are introduced from other fields, and the accuracy may be achieved in the fields used by these methods. However, due to the reasons such as the soil bulk density, texture, salt content, soil structure variability, and soil stratification, etc., To use it, it is necessary to carry out a large number of field calibrations on different soils and even different fields, different points, and different levels of the same point, and it is very difficult to calibrate the field. The application range of calibration results is also very narrow, and some methods such as resistance method, over time, As it passes, the calibration results tend to fail quickly. In addition, methods such as the TDR method satisfying the measurement accuracy requirements are very complicated and costly, which greatly limits the popularization and application of the methods. The causes of the above problems, when introducing the humidity measurement method for other substances, do not fully consider the complex and changing nature of the soil, especially the spatial variability of the physical and chemical properties of the soil. When it is found that there are problems, most of them are not based on physical mechanisms. Analysis and solution, but the introduction of soil physical and chemical correction and compensation curve solution. It should be pointed out that due to the complexity and variability of field soils, there is a certain amount of error in any method when measuring field soil moisture. This error is caused both by instrumentation techniques such as measurement techniques and soil moisture testers, as well as by the method itself. The former can be reduced or eliminated through technological improvements; for the latter, reducing it is very difficult. Therefore, the core of the problem is to determine whether the error of different methods in the general physicochemical variation of farmland is large and whether it is within the allowable range. This is the key to determine whether a method has the potential for further research. As the object of study, the soil is very complex and changeable, this study should not start from a specific method of experimentation, but should be based on the theoretical analysis of the physical mechanism. From the perspective of physical mechanism, various existing electromagnetic measurement methods, although their specific principles are different from each other, are all based on the principle of interaction between electromagnetic waves and soil. At this point, the general principles are unified. In the broad electromagnetic spectrum, the electromagnetic properties of all substances, including soil, can be summarized by electromagnetic parameters that reflect the interrelationships between the material's electrical polarization characteristics, complex permittivity, complex refractive index, Lambertian absorption coefficient, and mass absorption coefficient. Therefore, by analyzing the moisture sensitivity of these electromagnetic parameters and the effects of soil texture, bulk density and salt content on them, we can avoid the entanglement of various specific technical methods and correctly estimate the potential for further research on various soil moisture electromagnetic measurement methods. . At the same time, this is a comprehensive issue involving the electromagnetic properties of soil and electronic measurement technology. It is necessary to analyze and inspect the moisture measurement technology of other materials at present, and to combine the electromagnetic properties of soil moisture and the sensing and testing technology to conduct research. This is a future study. The direction.
The rapid and convenient measurement of soil moisture is an important issue in agricultural science and technology. As early as the beginning of this century, a large number of studies have been conducted at home and abroad, and dozens of methods have been proposed. So far, there are many studies on weight, energy, thermal properties, neutrons, impedance, capacitance, time domain reflectometry (TDR), microwave, near-infrared, optics, X-ray, and C-ray methods. The principle and method developed a soil moisture recorder and other instruments for measuring and recording soil moisture. From the impedance method to the C-rays, the eight methods are all based on the principle of interaction between the general electromagnetic wave and the soil, so it can be summarized as a generalized electromagnetic method. Because people have a deep understanding of electromagnetic waves, and modern electronic technology has provided strong technical support for its research, this is the most studied, most in-depth and most potential class of methods. Therefore, it is of great theoretical and practical significance to analyze the current status of research and explore its existing problems and new research approaches.