Question 1

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 for each other, not soil solids.

Question 2

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 is the maximum amount of water that soil can hold after excess water has drained away, and for most soils, the water potential at field capacity is between -10 and -30 kPa.

Question 3

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 4

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 5

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

Accepted Answer

Osmotic and matric potentials are negative because they represent the energy required to move water from a solution with a lower energy level (soil water) to a solution with a higher energy level (pure water). Therefore, the potentials are expressed as negative values.

Question 6

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

Accepted Answer

Capillary movement occurs as a result of the cohesive forces between water molecules and the adhesive forces between water and the material of the capillary tube.

Question 7

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 8

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 actually the opposite phenomenon where a soil's water content/potential relationship is different when it is being dried than when it is being wetted. This occurs because of differences in soil structure and pore size distribution during wetting and drying cycles.

Question 9

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 10

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

Accepted Answer

The osmotic potential is affected by the concentration of solutes in the soil, including salts.

Question 11

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

Accepted Answer

Gypsum or nylon blocks are designed to absorb moisture from the soil and are most effective in dry conditions where there is less competition for water in the soil.

Question 12

The adsorption of water on soil surfaces encourages capillarity.

Accepted Answer

When water is adsorbed on the soil surface, it creates a thin film of water molecules around soil particles which increases the surface tension and promotes capillarity. Capillarity refers to the ability of water to move against gravity in narrow spaces, such as soil pores, due to the attractive forces between water molecules and the surfaces of the soil particles. Therefore, water adsorption on soil surfaces encourages capillarity.

Question 13

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 14

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 both total soil porosity and the water-holding capacity of the soil, which affects the amount of water available to plants.

Question 15

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. It is a measure of the energy required to extract water from soil and is related to the soil water content, texture, and structure.

Question 16

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 17

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 of higher water potential (less negative) to a region of lower water potential (more negative). Therefore, water will move from a site with a water potential of -5 kPa to an adjacent site with a water potential of -40 kPa.

Question 18

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

Accepted Answer

The magnetic resonance technique, also known as nuclear magnetic resonance (NMR), can be used to estimate both soil moisture and salt content by analyzing the magnetic properties of the soil.

Question 19

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.

Quiz 5: Soil Water: Characteristics and Behavior