Hygeoscopic and combined water
Answers
Answer:
Both of these two types of water are unavailable for plants, although they are present in the soil.
Explanation:
Hygroscopic water is the water that is absorbed from the atmosphere and held very tightly by the soil particles so that it is unavailable to plants. Plants need water to survive. But they can't use this hygroscopic water because it has a tight bond with the soil particles.
The water, which is chemically combined in the structure of soil minerals, is known as combined water. After the elimination of hygroscopic water by heating soil to about 150°C., the only water that remains is in the hydrated oxides of aluminum, iron, silicon, etc.
This water is unavailable to the plants for taking and can only be driven off from the soil by resorting to a very high temperature. But it is not possible before bringing about irreversible changes in the physical and chemical composition of the soil itself.