Module 2: Soil Water Processes

Question 1

What are soil water processes?

Answer 1

A variety of processes that can happen when water arrives on the soil surface.
1) Puddling/run-off
2) Infiltration
3) Redistribution
4) Percolation/capillarity
5) Storage/Uptake by Roots/Evaporation
6) Drainage

Question 2

What is the hydrological cycle?

Answer 2

The hydrological cycle is the continuous cycling of water through the atmosphere, the Earth, and back into the atmosphere. It describes the movement and storage of water between the air, plants, soil and open water sources.

Question 3

Why are soil water processes important?

Answer 3

• SWP enable movement of air and nutrients through the soil.
• SWP are a filter of the water.
• SWP are like a sponge for the Earth, reducing flooding and storing water.

Question 4

What determines the effectiveness of SWP?

Answer 4

The soil texture and composition.

Question 5

What is soil porosity?

Answer 5

The capacity for soil to store water.

Question 6

What is soil water permeability?

Answer 6

The ease with which water can move through the soil.

Question 7

What are disruptors of SWP?

Answer 7

Soil crusting, soil water repellency, and soil compaction, soil sealing (naturally through e.g. lava or by humans through urbanistion).

Question 8

What are the consequences of SWP disruption?

Answer 8

Infiltration is inhibited leading to ponding on flat surfaces or run-off on hilly surfaces.
Second, plants can no longer grow which leads to poor quality vegetation or even bear soil. This will eventually lead to erosion.

Question 9

What is soil wettability?

Answer 9

A soil is wettable when it allows water to move into and throughout the soil.

Question 10

What are two common problems that reduce soil wettability?

Answer 10

Soil crusting and soil repellency.

Question 11

What are two key soil wettability processes?

Answer 11

Infiltration & redistribution.

Question 12

What are the risks when soil is not wettable?

Answer 12

Erosion, pollution, reduced crop performance.

Question 13

What are the two types of soil crusting? How does “…” soil crusting occur?

Answer 13

There can be biological and physical soil crusting. Physical soil crusting happens because of destruction of the soil structure. Soil particles are are suspended at the surface of the soil and this forms a hard crust.

Question 14

Which soils are most susceptible to physical soil crusting?

Answer 14

Finer textured soils (high clay content) that are low in organic matter.

Question 15

How does soil repellency emerge?

Answer 15

A waxy/oily coat emerges on the soil particles due to roots, leaves and soil organisms, often after a dry period.

Question 16

What is the WDPT test?

Answer 16

The water drop penetration time tests how long it takes for a droplet to be absorbed into the soil.

Question 17

What soils are more prone to water repellency?

Answer 17

Sandy soils - unsure why exactly…??

Question 18

What soil texture is more prone to developing severe water repellency?

Answer 18

Sandy soils.

Question 19

How does soil crusting differ from water repellency?

Answer 19

Crusting is due to the inorganic soil structure whereas repellency is caused by organic material in the soil.

Question 20

What is soil dispersion?

Answer 20

The breaking down of soil into finer particles.

Question 21

What is a common cause of soil water repellency?

Answer 21

Fires.

Question 22

What percentage of soil water repellent material can already disrupt SWP?

Answer 22

As little as 1%!!!

Question 23

Is water polar or non-polar? And what about soil?

Answer 23

Water is polar, and so is soil, and they are therefore attracted to each other. This attraction facilitates lateral and vertical movement of water through the soil.

Question 24

What is preferential flow?

Answer 24

Water only flows through channels that are wettable. Preferential flow interferes with effective water distribution.

Question 25

What is soil compaction?

Answer 25

Soil compaction is a process during which a pressure in put on the soil which pushes the particles close together.

Question 26

Where is soil compaction common?

Answer 26

Question 27

What does soil compaction alter? What consequences does that have?

Answer 27

The soil structure.
1) Pore spaces decrease –> reduced water and air flow –> reduces soil fauna.
2) Infiltration will be decreased.
3) Reduced water filtering through to the ground water.
4) Reduced root growth.

Question 28

How does soil organic matter relate to soil compaction?

Answer 28

High soil organic matter makes for soils more resilient to compaction.

Question 29

What are some bio-subsoilers to deal with compaction?

Answer 29

Lucerne, rapeseed, rye, rye-grass.

Question 30

What is soil sealing?

Answer 30

The soil is covered by artificial structures often for urban expansion. It disrupts the SWP.

Question 31

What are the negative effects of soil sealing?

Answer 31

• Food security is at risk due to the expansion of sealing on productive land.
• Urban heat effect: cities are hotter than rural areas.
• Malfunctioning water cycles: which implies e.g. flood risk is higher as there is not enough drainage capacity.