Chapter 6 Soil water

Question 1

When dry soil is crushed in the hand, it can be seen that it is composed of

Answer 1

all kinds of particles of different sizes.

Question 2

When dry soil is crushed in the hand, it can be seen that it is composed of all kinds of particles of different sizes.

Most of these particles originate from

Answer 2

degradation of rocks; they are called mineral particles.

Some originate from residues of plants or animals (rotting leaves, pieces of bone, etc.), these are called organic particles (or organic matter).

Question 3

The soil particles seem to touch each other, but in reality have

Answer 3

spaces in between.

Question 4

The soil particles seem to touch each other, but in reality have spaces in between. These spaces are called

Answer 4

pores

Question 5

When the soil is “dry”, the pores are mainly filled with

Answer 5

air

Question 6

After……………………………………….., the pores are mainly filled with water

Answer 6

irrigation or rainfall

Question 7

Living material is found in the soil. It can be …………………………………………………………..

Answer 7

live roots as well as beetles, worms, larvae etc.

Question 8

living materials help to…………………….. and thus……………………………………………..

Answer 8

aerate the soil and thus create favourable growing conditions for the plant roots

Question 9

The following image represents

Answer 9

The composition of the soil

Question 10

A represents

Answer 10

Soil Particles

Question 11

B represents

Answer 11

water

Question 12

C represents

Answer 12

air

Question 13

D represents

Answer 13

root

Question 14

If a pit is dug in the soil,………………………………………………………………………….. can be seen.

Answer 14

1. At least 1 m deep,
2. Various layers,
3. Different in colour and composition

Question 15

If a pit is dug in the soil, at least 1 m deep, various layers, different in colour and composition can be seen. These layers are called

Answer 15

horizons

Question 16

the profile of the soil:

Answer 16

succession of horizons

Question 17

soil profile:

Answer 17

1. The plough layer
2. The deep plough layer
3. The subsoil layer
4. The parent rock layer

Question 18

The following image represent the

Answer 18

Soil profile

Question 19

A represent

Answer 19

Plough layer

Question 20

B represents

Answer 20

Deep plough layer

Question 21

C represents

Answer 21

Subsoil layer

Question 22

D represents

Answer 22

The parent rock layer

Question 23

Name of the particles:

gravel

Size limits in mm:

Answer 23

larger than 1

Question 24

Name of the particles

gravel

distinguishable with the naked eye:

Answer 24

Obviously

Question 25

**Name of the particles:** sand **size** **limit** **in mm:**

Answer 25

1 to 0.5

Question 26

**Name of the particles:** sand **Distinguishable with naked eye:**

Answer 26

easily

Question 27

**Name of the particles:** silt **Size limits in mm:**

Answer 27

0.5 to 0.002

Question 28

**Name of the particles:** silt **Distinguishable with naked eye**

Answer 28

barely

Question 29

**Name of the particles:** clay **Size limits in mm:**

Answer 29

less than 0.002

Question 30

**Name of the particles:** clay **Distinguishable with the naked eye:**

Answer 30

impossible

Question 31

......................................determines the soil texture.

Answer 31

The amount of sand, silt and clay present in the soil

Question 32

In ............................textured soils: .............................. is predominant (sandy soils).

Answer 32

coarse sand

Question 33

In ......................... textured soils: ...................is predominant (loamy soils).

Answer 33

medium silt

Question 34

In .......................textured soils: .......................is predominant (clayey soils).

Answer 34

fine clay

Question 35

In the field, soil texture can be determined by

Answer 35

rubbing the soil between the fingers

Question 36

Soil structure refers to or soil structure refers to

Answer 36

the grouping of soil particles (sand, silt, clay, organic matter and fertilizers) into porous compounds. These are called aggregates or Soil structure also refers to the arrangement of these aggregates separated by pores and cracks

Question 37

When present in the topsoil, a massive structure

Answer 37

blocks the entrance of water

Question 38

When present in the topsoil, a massive structure blocks the entrance of water; seed germination is difficult due to

Answer 38

poor aeration

Question 39

if the topsoil is ....................................., the water enters easily and the seed germination is better

Answer 39

granular

Question 40

The following soil structure is

Answer 40

Grangular

Question 41

The following soil structure is

Answer 41

Blocky

Question 42

The following soil structure is

Answer 42

Prismatic

Question 43

The following soil structure is

Answer 43

Massive

Question 44

In Granular soil structure the flow is ..........................

Answer 44

rapid

Question 45

In Blocky soil structure the flow is ..........................

Answer 45

moderate

Question 46

In Prismatic soil structure the flow is ..........................

Answer 46

moderate

Question 47

In Massive soil structure the flow is ..........................

Answer 47

Slow

Question 48

The depth of the ..........................................varies greatly from place to place, mainly due to changes in ......................................

Answer 48

groundwater table topography of the area

Question 49

In one particular place or field, the depth of the groundwater table may vary in ............

Answer 49

time

Question 50

A perched groundwater layer can be found

Answer 50

on top of an impermeable layer rather close to the surface (20 to 100 cm)

Question 51

A perched groundwater layer can be found on top of an impermeable layer rather close to the surface (20 to 100 cm). It covers usually a .......................area.

Answer 51

limited

Question 52

The top of the perched water layer is called the

Answer 52

perched groundwater table

Question 53

A represents

Answer 53

Soil surface

Question 54

B represents

Answer 54

Perched water layer

Question 55

C represents

Answer 55

Compacted layer

Question 56

D represents

Answer 56

ground water table

Question 57

Infiltration:

Answer 57

The movement of water from the soil surface into the soil

Question 58

Redistribution:

Answer 58

The subsequent movement of infiltrated water in the unsaturated zone of a soil.

Question 59

Redistribution involve:

Answer 59

1. Exfiltration 2. Capillary rise 3. Recharge 4. Interflow

Question 60

exfiltration

Answer 60

evaporation from the upper layer of the soil

Question 61

capillary rise

Answer 61

movement upward from the saturated zone to the unsaturated zone due to surface tension

Question 62

recharge

Answer 62

movement of water from the unsaturated zone to the saturated zone

Question 63

interflow

Answer 63

flow that moves downslope

Question 64

Infiltration and redistribution depend critically on.......................................................

Answer 64

the material and hydraulic properties of soils

Question 65

The groundwater can be sucked ..............................by the soil through ................................... that are called ..............................

Answer 65

upward very small pores that are called capillars .

Question 66

The groundwater can be sucked upward by the soil through very small pores that are called capillars. This process is called ..........................

Answer 66

capillary rise

Question 67

Soil texture: Coarse (sans) Capillary rise (in cm):

Answer 67

20 to 50 cm

Question 68

Soil texture: medium Capillary rise(in cm):

Answer 68

50 to 80 cm

Question 69

Soil texture: fine (clay) Capillary rise (in cm):

Answer 69

more than 80 cm up to several meters

Question 70

Darcy’s Law states that the flow rate in the horizontal depends on

Answer 70

(1) the ability of the soil to “conduct” water; (2) the magnitude and direction of the slope, which is the gravitational potential energy gradient per unit weight of flowing water (soil water wants to flow downhill, towards lower gravitational potential energy), and (3) the magnitude and direction of the horizontal gradient in soil water pressure (if soil water pressure decreases in the x direction, the water wants to flow in that direction).

Question 71

hydraulic conductivity

Answer 71

the vertical flow rate depends on the sum of the gravitational potential energy gradient per unit weight of water (dz/dz =1) and the vertical gradient in soil water pressure.

Question 72

In a steady state (qz equals ...............)

Answer 72

zero

Question 73

there is a balance between ................................. and ....................................

Answer 73

the effect of gravity an upward decrease in soil water pressure

Question 74

the effect of gravity (which always wants to .......................................of ...................................., .towards...............)

Answer 74

pull the water “down the gradient” gravitational potential energy lower z

Question 75

an upward decrease in soil water pressure (“................. the gradient” is in the .......................... z direction).

Answer 75

down positive

Question 76

if the effect of gravity and an upward decrease in soil water pressure don't balance there is

Answer 76

a vertical water flow (up or down, depending on which term “wins”), the magnitude of which depends of the size of the imbalance and the value of the hydraulic conductivity coefficient.