1. Principle of soil moisture sensor.
At present, the principles of soil moisture measurement mainly include standing wave method, TDR time domain reflection method, FDR frequency domain reflection method, etc., especially FDR frequency domain reflection method is more accurate and cost-effective. The main technical principle is to measure soil moisture by using high frequency line to measure the dielectric constant of soil moisture. At present, most of the needle soil moisture sensors we see on the market adopt this principle. From the author's experience, the accuracy can be simply judged by the number of stainless steel probes (4 needles > 3 needles > 2 needles).
2. Is the value measured by soil moisture sensor relative water content?
Give the answer first: No.
At present, the needle type soil moisture sensor, which is widely purchased in the market, should be the volume moisture content of soil, not the relative moisture content, according to the analysis of appearance shape and description principle. For professional customers (especially those who are concerned about soil moisture, scientific research, water and fertilizer), most of them are concerned about the relative soil moisture content. How to get the relative soil water content that customers want by measuring the soil volume water content.
Formula: Soil volume water content = soil weight water content * soil bulk density
Soil relative water content = soil weight water content / field capacity
Among them, soil bulk density and field water capacity are related to soil structure, texture, organic matter content and soil utilization. Therefore, it is necessary to obtain the data of soil bulk density and field water capacity in order to correctly give the data of soil relative water content. If a simple needle soil sensor directly gives the relative water content of soil, it is not necessary to believe too much.
3. The role of soil moisture sensors in Agricultural Internet of things projects.
It works a lot. For example, it has an impact on irrigation. For example, relatives in my hometown ask you: how to calculate the maximum irrigation water of drip irrigation crops per mu? For example, how much water do we need to irrigate if we want to moisten soil vegetation at a depth of 40 cm? To solve these practical problems, we need to use the knowledge of soil moisture. In production, we will rely on modern soil moisture monitoring equipment to monitor the soil moisture status and control irrigation. Of course, in addition to the above-mentioned knowledge of soil bulk density and field capacity, if the irrigation amount is corrected, it will also involve the knowledge of wilting coefficient, transpiration and so on. But no matter what, the first thing to do is to make sure that the data of the soil moisture sensor is correct.
A small soil moisture sensor, the value of goods is not high, but it involves a lot of knowledge points. It needs the manufacturer to have the corresponding knowledge of Agronomy, electronics and soil science to be able to give users the correct data and suggestions. I hope you can make a lot of criticisms and corrections to jointly promote the progress and development of domestic agricultural information instruments.
