Module 11: Water and Soils

Question 1

What is pore volume?

Answer 1

Space taken up by air and water in the soil

Question 2

What is porosity?

Answer 2

Percentage of air and water volume in soil

Question 3

What is infiltration or drainage?

Answer 3

The downward movement of water into the soil

Question 4

What is infiltration rate?

Answer 4

Speed of which water moves into a soil (mm/hr)

Greater in sand than clay

Question 5

What is saturated soil?

Answer 5

All pores in the soil are filled with water

Question 6

What is gravitational water?

Answer 6

Water that drains or moves down the soil profile due to gravity.

Volume of water between saturation and field capacity = gravitational water

Not usually available to plants

Question 7

What is soil at field capacity?

Answer 7

Soil after the removal of gravitational water

It contains the maximum amount of water available to plants

Question 8

What is capillary water?

Answer 8

Water retained in soil pores after removal of gravitational water

Surface tension (suction) holds the water around the soil particles

Question 9

What is the permanent wilting point?

Answer 9

Point at which the plant can no longer absorb any water.

As some capillary water is removed by evaporation and plant absorption, surface tension increases until the plant can no longer absorb water.

The force holding water to soil particles is stronger than roots’ absorption force.

Question 10

What is the available water capacity?

Answer 10

Volume of water that can be used by the plant.

The volume of water between field capacity and permanent wilting point

Question 11

What is the groundwater table?

Answer 11

Top of the layer/top boundary of the permanently saturated soil

Question 12

What is a perched groundwater table?

Answer 12

Top of a water layer/top boundary above the impermeable layer (hardpan) and is near the soil surface (20 to 100cm)

Question 13

What is a capillary rise?

Answer 13

Upward movement of water

In clay, it rises slower but rises a greater distance. In sand, it rises faster but rises a shorter distance

Question 14

What are the two ways water is added to the soil?

Answer 14

Rainfall and irrigation

Question 15

What are the ways water is removed from the soil?

Answer 15

Transpiration, evaporation, drainage, and surface runoff

Question 16

What are the factors that affect the infiltration rate?

Answer 16

Soil texture, soil moisture content, soil structure

Question 17

If the soil feels wet, what does that say about the soil water content?

Answer 17

Higher than field capacity

Question 18

If the soil feels moist, what does that say about the soil water content?

Answer 18

Between field capacity and permanent wilting point

Question 19

If the soil feels dry, what does that say about the soil water content?

Answer 19

Below permanent wilting point

Question 20

How do you measure the moisture content in soil?

Answer 20

Sample is weighed and dried for 24 hours in an oven at 105C then weighed again

% water = weight of moist soil - weight of oven dried soil) / weight of oven dry -> everything multiplied by 100%

Question 21

What determines the depth of the groundwater table?

Answer 21

It varies according to location especially due to topography.

In one place, it can vary in time (temperature, etc)

Question 22

What is the soil moisture content?

Answer 22

Percentage of mass of soil that is made up of water

Question 23

How do you calculate porosity?

Answer 23

Pore volume is divided by soil volume. Multiplied by 100%