Question 1

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

Accepted Answer

Magnetic resonance technique can detect water and ions in the soil, thus can determine both soil moisture levels and salt contents.

Question 2

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 3

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

Accepted Answer

The matric potential is indeed due to the attraction of water molecules to soil solid surfaces, particularly in small pore spaces in the soil. This attraction results in a decrease in the energy of the water molecules, which in turn creates a negative pressure or tension in the soil water.

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

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 best for estimating soil water content when the soil is dry because they can absorb water from the soil and change in size or weight, indicating the water content of the soil. However, when the soil is already wet or saturated, they may not be as accurate in estimating the soil water content.

Question 6

The adsorption of water on soil surfaces encourages capillarity.

Accepted Answer

When water is adsorbed on soil surfaces, it forms a thin film around the soil particles. This increases the surface area available for capillary action, which pulls water from deeper layers of soil upwards towards the plant roots. Hence, the adsorption of water on soil surfaces encourages capillarity.

Question 7

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 8

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 9

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

Accepted Answer

The osmotic potential is indeed dependent upon the presence of salts and other solutes in the soil. These solutes create a concentration gradient that affects the movement of water through plant cells.

Question 10

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 to a region of lower water potential. Here, the water potential at the starting site (-5 kPa) is higher than the water potential at the adjacent site (-40 kPa). Therefore, water will move from the site with -5 kPa to the site with -40 kPa.

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 (when the soil is saturated and excess water has drained away) for most soils is typically in the range of -10 to -30 kPa.

Question 12

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 refers to the situation where the relationship between soil water content and potential is different during wetting and drying processes. During wetting, the soil requires a lower potential (i.e. more water) to achieve a given water content than during drying. This is due to factors such as the rearrangement of soil particles and the filling of pore spaces during wetting which lead to a reduction in air-filled porosity and an increase in effective porosity. During drying, the reverse occurs, with the soil requiring a higher potential to achieve a given water content.

Question 13

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

Accepted Answer

Capillary movement is indeed made possible by the processes of cohesion (the attraction between molecules of the same substance) and adhesion (the attraction between molecules of different substances). This phenomenon is what allows liquids such as water to flow through narrow spaces, such as in the tiny tubes of plants or the pores of soil.

Question 14

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 for soil solids.

Question 15

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 16

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 the solutes or the soil matrix exert a lower energy level on the water compared to pure water, resulting in a reduction of the water potential.

Question 17

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 improve soil structure and increase the amount of pore spaces available for water retention, as well as enhance water-holding capacity and supply nutrients to plants, leading to increased water availability for plant growth.

Question 18

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 19

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.

Quiz 5: Soil Water: Characteristics and Behavior