Common ways of measuring soil moisture: Gravimetric method, volumetric water content and tensiometric method
STEP Systems News March, 2021
Soil Moisture Measurement
Essential parameter for an optimal plant growth
Water supply has a fundamental influence on the development of your plants. Sufficient moisture level in the root zone assures that nutrients in the soil are at their best availability and supports healthy plant nutrition and optimal growth. In reverse, a lack of soil moisture disturbs the nutrient uptake of plants and often causes a nutrient deficit.
Regardless of tasks you are facing, whether the soil moisture level should be reduced or increased, following questions should be answered in order to find an optimal solution:
How to control where and how much water is buffered in the soil?
How to know when roots can get the right amount of water?
Common ways of measuring soil moisture:
It is usually used in laboratory: taking a soil sample, weighing, drying until the weight is constant, weighing again. Calculation the loss of weight in percent (absolute value).
Volumetric Water Content
VWC is a capacitive measurement, indicating how much water is in the soil in relation to the soil volume. The unit is usually expressed as a percentage in relation to the volume of the soil or growing media. This percentage figure may not be compared to the percentage determined gravimetrically because a completely water-saturated soil has max. about 55% VWC. Consequently, the interpretation of the measured results depends extremely on the soil structure and the soil type. Most common VWC measurement methods are TDR (Time Domain Reflectometry) and FDR (Frequent Domain Reflectometry).
Soil moisture tension shows how easy it is to extract water from soil. When the soil is saturated there is plenty of water in the pore spaces and plenty of water coating the soil particles. This moisture makes it very easy for plant roots to absorb water. In this case the soil moisture tension is low. The tensiometric tension is negative or under pressure. It is measured with analogue or digital manometers and expressed in hectopascal or mbar. Tensiometric measurement reflects in the best way the possible uptake of water from the plant.
The SWM 5000 provides fast and precise determination of soil moisture, for example in sandy, loamy, clayey, silty soils. The sensor length is 100 cm, thus, the volume water content of the lower layers can also be taken into account during irrigation management. More info →