Question 1

Osmotic and matric potentials are commonly negative because the soil water has a lower energy level than that of pure water.

Accepted Answer

Osmotic potential is negative because solutes in the soil water lower the energy level compared to pure water, and matric potential is negative because soil particles hold onto water molecules tightly, creating a lower energy state than pure water.

Question 2

The soil water potential is a measure of the potential of a soil to hold water.

Accepted Answer

Soil water potential is a measure of the energy status of water in soil, indicating how freely water is available to plants, rather than the soil's capacity to hold water.

Question 3

Hysteresis is the phenomenon whereby a soil has the same water content/potential relationship when it is being dried as when it is being wetted.

Accepted Answer

Hysteresis is the phenomenon whereby a soil does not have the same water content/potential relationship when it is being dried as when it is being wetted. This is because the soil structure changes during wetting and drying cycles.

Question 4

The adsorption of water on soil surfaces encourages capillarity.

Accepted Answer

The adsorption of water molecules onto soil surfaces creates a thin film of water around soil particles, which increases the strength of the attractive forces between soil particles and encourages capillarity.

Question 5

Filling the bottom half of a flower pot with gravel will greatly improve the aeration of the soil-mix in the top half.

Accepted Answer

Adding gravel to the bottom of a pot can actually impede water drainage and create an environment where water collects, potentially leading to poorer aeration and root health.

Question 6

Plant roots gain access to soil water primarily by the growth of the roots into moist soil.

Accepted Answer

The answer of Plant roots gain access to soil water...

Question 7

The matric potential is due to the attraction of water molecules to soil solid surfaces.

Accepted Answer

Matric potential is indeed due to the attraction of water molecules to soil solid surfaces. This attraction causes water to be held tightly by the soil particles, leading to a negative pressure potential.

Question 8

The osmotic potential is dependent upon the presence of salts and other solutes in the soil.

Accepted Answer

The osmotic potential is a measure of the tendency of water to move from a solution of lower solute concentration to one of higher solute concentration. Therefore, the presence of salts and other solutes in the soil affects the osmotic potential.

Question 9

The tenacity with which water is held in soils is directly related to the soil moisture content, the higher the moisture level the greater the attraction of the water to the soil.

Accepted Answer

The tenacity with which water is held in soils is related to the soil's texture and structure, not directly to the soil moisture content. Finer-textured soils like clay hold water more tightly than coarser soils like sand, regardless of the moisture level.

Question 10

Capillary movement is made possible by the processes of cohesion and adhesion.

Accepted Answer

Capillary movement occurs due to the combined forces of cohesion (attraction between water molecules) and adhesion (attraction between water molecules and the surface of the capillary tube or material).

Question 11

The water potential at the field capacity for most soils is in the range of -10 to -30 kPa.

Accepted Answer

This statement is true. The water potential at field capacity, which is the point where soil is filled with the maximum amount of water it can hold, is typically in the range of -10 to -30 kPa. Beyond this point, any additional water will drain out of the soil due to gravity.

Question 12

Gypsum or nylon electrical resistance blocks are most useful in estimating the soil water content if the soil is quite dry.

Accepted Answer

Gypsum or nylon electrical resistance blocks are most useful in dry soils because they rely on the soil's ability to conduct electricity, which is reduced in wet soil. In wet soil, other methods such as tensiometers or capacitance probes are more effective in measuring soil water content.

Question 13

The property of cohesion in water stems from the attraction of water molecules for soil solids.

Accepted Answer

The property of cohesion in water stems from the attraction of water molecules to each other, not to soil solids.

Question 14

Although the total soil water content of a clay soil is about the same as a nearby well structured silt loam, the clay will likely provide more available water to plants because of its higher volume of small pores.

Accepted Answer

Clay soils have smaller pores which hold water more tightly than the larger pores in silt loam soils, making it harder for plants to extract water from clay soils.

Question 15

The hydrogen end of a water molecule is attracted to positively charged cations such as Na⁺ and Ca²⁺.

Accepted Answer

The hydrogen end of a water molecule is positively charged and is attracted to negatively charged anions, not positively charged cations.

Question 16

The effect of soil organic matter on the amount of water available to plants is due to organic matter influence on total soil porosity as well as to the water-supplying power of the soil organic matter.

Accepted Answer

Soil organic matter can increase soil porosity, which allows for better water movement and storage, and can also increase the water-holding capacity of the soil itself. Therefore, the statement is true.

Question 17

Water molecules have polarity primarily because each contains two H atoms and only one O atom.

Accepted Answer

Water molecules have polarity because of the difference in electronegativity between the hydrogen atoms and the oxygen atom, leading to an uneven distribution of charge.

Question 18

The magnetic resonance technique of estimating soil moisture levels can also be used to estimate salt contents.

Accepted Answer

Magnetic resonance imaging (MRI) can measure both soil moisture and salt content by detecting the different proton signals given off by water and salt molecules.

Question 19

The polarity of water helps account for the attraction of water molecules for each other.

Accepted Answer

The polarity of water results in a partial positive charge on the hydrogen atoms and a partial negative charge on the oxygen atom, which leads to attraction between water molecules. This phenomenon is known as hydrogen bonding.

Question 20

Water will move from one site in a soil with a water potential of -5 kPa to an adjacent site with a water potential of -40 kPa.

Accepted Answer

Water always moves from a region with a higher water potential (less negative) to a region with a lower water potential (more negative). In this case, -5 kPa has a higher water potential than -40 kPa, so water will move from the former to the latter.

Quiz 5: Soil Water: Characteristics and Behavior