1) Imagine a root of a cotton plant growing in the upper horizon of an irrigated
ID: 115294 • Letter: 1
Question
1) Imagine a root of a cotton plant growing in the upper horizon of an irrigated soil in California's Imperial Valley. As the root attempts to draw water molecules from this soil, what forces(potentials) must overcome? If this soil were compacted by heavy vehicle, which of these forces would be most affected? Explain. 2) Using the terms adhesion, cohesion, meniscus, surface tension, atmospheric pressure, and hydrophilic surface, write a brief essay to explain why water rise up from the water table in a mineral soil 3) Give four reasons why compacting a soil is likely to reduce the amount of water available to growing plantsExplanation / Answer
1)
The Xylem tissue present in the roots of the plants transport water and minerals and in order to draw water molecules four forces come into play, these are:
The combined effect of all these forces should be positive in order to move water up in the plants.
If soil is compacted then the only positive pressure i.e. pressure potential or turgor potential or turgor pressure(positive or negative) can become negative because the positive pressure inside cells is contained by the cell wall, producing turgor pressure in a plant will decreses due to compaction.
2)
Due to adhesive forces beween molecules of water and hydrophilic surface of xylem and cohesive forces between water-water and xylem-xylem surface, the water form concave meniscus in the very fine radius' capillary tubes of the roots and because of this high surface tension develop between water and xylem molecule which overcomes the atmospheric pressure and hence water rise up from the water table in a mineral soil.
3)
Compacting a soil reduces the amount of water available to plant by:
a. By decreasing the pressure potential or turgor potential.
b. It also decreases the matric potential and makes it more negative.
c. Solute potential also become more negative with compaction of soil.
d. The porosity of the soil also decreases with compaction and hence the water present in the soil decreases which again decreases water available to plant.
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