If a liquid like water is present in a way of tiny drops, in air, in a substance or on a surface we called it as moisture. But it is very difficult to define the “soil moisture”. Normally, soil moisture can be defined as the water that retain in between the spaces of the soil and rock particles. This is of two types. Those are
Surface soil moisture is the water that is available in the upper 20cm of the soil surface.
Root zone moisture is the moisture available in the upper 200cm of the soil surface. This is the moisture that is available for the plants.
Most of the time except in using hydroponics or aeroponic techniques most people use soil as their medium for vegetation growth. The plants absorbs water for their usual and essential activity of photosynthesis and also for the growth. The root network that penetrate in to the soil does this job. Therefore prevalence of water in the soil is very vital.
If water is present in very little or excess amount it is very bad for the crop growth. The water should be of optimum amount to efficient growth of the plants. So knowing the moisture content in the soil plays a critical role in maintaining a better crop stand. When it comes to the modern agriculture there are several ways of measuring this soil moisture. But before knowing these methods first we are going to understand the importance of measuring this soil moisture content.
Importance of measuring soil moisture
As I mentioned earlier also we all know that in most of the time people use soil as their medium for growing plant and of course water is a critical factor for agriculture. If plant experience a lack or excessiveness of water it will be stressed. Therefore it is very important for us to know whether the plant possess enough or optimum quantity of water. So there comes measuring of soil moisture. Measuring of soil moisture will allow optimum use of water. We already know that water is a limited resource to the world. Most of the people around the world depend on irrigation water and engage in rain fed cultivation. But sustainable use of this water is very important. So by measuring soil moisture it will allow for sustainable and efficient use of water. Because we only have to supply the needed amount of water by the crop. Wastage of water can be minimized through this method. This measuring is very important for the areas where water is lacking and also during drought periods
With the increasing population we need to cultivate ore and more using the scare resources including water. So it is better if people can use the technique of measuring soil moisture and facilitating the use of only the required amount of water to their crops.
So here comes some soil moisture measuring sensors. Soil moisture sensors generally measure the amount of the soil water in a volumetric or gravimetric method. Here uses capacitance which measures the dielectric permittivity of the soil. Most of the sensors gives this volumetric content of water as a percentage.
Soil Moisture Sensors
There are mainly two types of Soil Moisture Sensors (SMS)
- Tensiometric SMS
- Volumetric SMS
Tensiometric Soil Moisture Sensors
Tensiometric SMSs measures the tension of the soil. That means it measures the capacity of the respective soil particle to attach moisture. Therefore we can introduce this as a sensor which is sensitive to characteristics of the soil.
Tensiometers and gypsum blocks can be identify as the tensiometric SMSs.
If I am to describe about the tensiometric SMS it consist of a probe that can be filled with water and this probe has two parts. The lower part is a ceramic tip that is porous and the above part is consist of a gauge. The tube is inserted in to the soil at the depth of the roots. Then the water inside the probe will leave through the porous tube until the moisture inside and outside will be in an equilibrium. At the time of the equilibrium the tension will be recorded in the gauge. If this reading is higher it says that the soil is dry. Because when the soil is dry the plant has to use more suction power to absorb water. Therefore the reading is higher which record the suction power.
Volumetric Soil Moisture Sensors (VSM)
Volumetric soil moisture measures the actual amount of water in the soil instead of measuring the soil moisture tension.
Time Domain Reflectrometry, Frequency Domain Reflectrometry and VH400 Soil Moisture Sensor can be identify as VMSs.
This VMSs measures the capacitance or the electrical permittivity of the soil.