When we refer to soil moisture, we talk about the water content in the soil and there are many types of soil moisture. One cannot get rid of the moisture in the soil all over because of which the types of soil moisture are examined prior to determining whether or not they are usable for a certain purpose. Sometimes one needs to know of the types of soil moisture for construction purposes while at other times this may be the case because of the fact that one would like to garden or grow crops in these soils and at these sites.
There are many types of soil moisture and one of these is gravitation water. These types of soil moisture occur freely in the soil and due to the force of gravity. You can find these in the macropres of the soil but they cannot be used by the plants on the soil as they go down the drain very fast. However, in compact soil the plants can use these because the water is trapped in the soil and is held together as well. These types of soil moisture occur merely due to the force of gravity which attracts such water.
Then are those types of soil moisture that are held in micropores of the soil and the water is held in the soil because of the fact that the surface tension in the micropores are much stronger than the gravitational force itself. Once the size of the pores increase, the water drains out and the capillary water is turned into gravitation water instead. As a result what happens is that the water goes down the water table just as it does and was explained in the previous of the types of soil moisture in the soil.
Another of the various types of soil moisture is hygroscopic water. What happens is that some soils cannot absorb water because of the fact that they consist of very little to no pores of their surface- clay soil being an example of this- and so the water cannot enter the soil particle. They just form a thin film of water around the soil instead and is not absorbed or used by the soil at all. You can use these in clay soils and these types of soil moisture were used in the past to extract water in times of drought and famine too.
These are just some types of soil moisture though there may be many others out there. What happens in some cases is that a site may need to be excavated and so the soil moisture is examined so that one can determine whether or not the site can support the foundations of the building. The examination of these types of soil moisture also helps determine how useful soil would be for plants, crop growth and such like. By way of example, one cannot grow plants easily in soils where hygroscopic water exists because the plant wouldn’t get the nutrients it needs to survive.