Methods of Measuring Soil Moisture
How do you measure soil moisture ? Soil is a vital natural resource essential for human survival, serving as the foundation for plant growth and development. The health of the soil environment directly impacts the sustainability of human societies. Apart from hydroponic plants, soil water remains the primary source for plant water uptake. It influences the dissolution and absorption of fertilizers as well as the decomposition and transformation of organic matter.How to measuring soil moisture ?
Researchers measure soil moisture content. This shows the percentage of water weight compared to soil weight. Understanding soil moisture content is crucial in determining crop water requirements, which holds significant importance for agricultural productivity. Current ways to measure soil moisture include the drying and weighing method, tensiometer method, and resistance method. Other methods are the neutron method, gamma ray method, and standing wave ratio method. There are also the optical method, time domain reflectometry (TDR), and frequency domain reflectometry (FDR). The drying and resistance methods are among the most widely used for their simplicity.
TDR Method:
Time Domain Reflectometry (TDR) emerged in the 1980s as a method for soil moisture measurement. It gained popularity internationally and recently entered China, quickly garnering attention across various sectors. TDR is effective for rapid soil moisture monitoring through time-domain transmission technology. This method operates on the principle that a waveform on a mismatched transmission line results in a combined effect of both original and transmitted waveforms. TDR’s response time ranges from 10 to 20 seconds, making it suitable for mobile and fixed-point monitoring.
The TDR method offers strong independence from environmental factors like soil type, density, and temperature. A notable advantage is its capability to measure soil moisture under freezing conditions, distinguishing it from other methods. Moreover, TDR can simultaneously assess soil moisture along with salt content accurately.
FDR Method:
The high-frequency oscillation method, or FDR (Frequency Domain Reflectometry), was developed slightly after TDR. Because TDR equipment was very expensive at first, companies like AquaSPY and Sentek looked for simpler options. These options could measure the dielectric constant of soils. The FDR method is not only more cost-effective than TDR but also offers quicker measurement times. After calibrating the soil, FDR gives accurate measurements. It can easily analyze multiple depths at the same time.
The FDR method uses electromagnetic pulse principles to measure the soil’s apparent dielectric constant through electromagnetic wave propagation frequency, determining soil volumetric water content.
Drying Method:
The drying method is a standard technique for determining soil moisture. This means taking a soil sample from the field. Then, dry it in an oven at 105°C. Keep drying until the weight stays the same. The weight difference before and after drying indicates the moisture content. The formula for calculation is: Soil water content = (W/M) × 100%. Here, M is the initial soil weight. W is the moisture weight. You find W by subtracting the dry soil weight (M’) from M.
Resistance method:
The electrical resistance method uses the resistance of materials like gypsum, nylon, and glass fiber. Their resistance changes with water content. When you insert these materials, along with electrodes, into moist soil, they eventually achieve moisture equilibrium with their surroundings. We have previously established a calibration between resistance and water content percentage. Using these components, we can obtain moisture readings within a suction range of 1 to 15 atmospheres.
Although the drying method delivers precise measurements, it falls short in terms of real-time performance. You can use a soil temperature and humidity sensor for quicker measurements. These sensors work using methods like Time Domain Reflectometry (TDR) or High Frequency Oscillation (FDR). They provide accurate, real-time readings of soil moisture content.
Monitoring soil moisture extends beyond agriculture into various engineering fields. Industries like railways, highways, hydropower stations, and construction also rely on soil moisture data.how do you measure soil moisture? For situations requiring precise data with ample time, the traditional drying method is suitable. For immediate soil moisture information, the TDR/FDR soil moisture sensors are ideal.
