Transport in soil

Question 1

Why do different soil horizons have different water-holding capacities?

Answer 1

Water retention is affected by varying:
- OM content
- Particle sizes

Question 2

Sandy soils:
- Allow rapid pollutant transport
- Increase contamination risk

Why?

Answer 2

Large pores

Question 3

Clay & OM:
- retain pollutants
- reduce contamination risk

Why?

Answer 3

high surface area and adsorption capacity

Question 4

Field capacity (FC)

Answer 4

Water that is held in the soil against gravitation, after it has been saturated and allowed to drain freely

Question 6

Saturated hydraulic conductivity (Ks, Ksat)

Answer 6

A measure of a soil’s ability to transmit water when the soil is fully saturated with water

The rate at which water can move through the soil when saturated

Question 7

Hydraulic conductivity

Answer 7

A measure of a soil’s ability to transmit water through its pore spaces-

Question 8

Available water

Answer 8

he portion of water that can be readily absorbed by plant roots

Field capacity - wilting point

Question 9

Effective porosity

Answer 9

Interconnected pores that allow for fluid movement

Question 10

pF curve

Answer 10

soil water retention curve

Question 11

Adhesion forces are particularly strong in…

What are the affect of adhersion forces?

Answer 11

soils with small pores (micropores), where water is held tightly against gravitational forces.

Question 13

• Capillary action

Answer 13

Water moves upward through the soil against gravity, supplying moisture to plant roots.

Question 14

Capillary Forces

Answer 14

Interaction of cohesion and adhesion forces, enabling the movement of water within the soil through capillary action.

water moves upward or sideways in soil due to surface tension and the attraction between water molecules and soil particles.

Question 15

Capillary rise (hc)

Answer 15

The height to which water rises in a narrow tube or soil pores due to capillary action.

Question 16

Drainable, available and not available water are a product of…

Answer 16

pore size distribution

Question 17

… → ↑Ks → ↑Water flow

Answer 17

↑coarse pores → ↑Ks → ↑ Water flow

Question 18

↑coarse pores → ↑Ks → …

Answer 18

↑coarse pores → ↑Ks → ↑Water flow

Question 19

↑coarse pores → … → ↑ Water flow

Answer 19

↑coarse pores → ↑Ks → ↑ Water flow

Question 20

Water flow through one large pore is equal to the water flow through … small pores.

Answer 20

Water flow through one large pore is equal to the water flow through 10,000 small pores.

This shows how much more effective large pores are at transporting water.

Question 21

Cross-sectional flow area

Answer 21

This is the total area through which water can flow in the soil

Question 22

Unsaturated hydraulic conductivity (K unsat )

Answer 22

A measure of the soil’s ability to transmit water when it is not fully saturated.

↓Soil water content → ↓Ksat

Question 23

There is a lot of focus recently on the effective porosity and hydraulic conductivity

Why?

Answer 23

Volume of macroporosity: 1-2%
Share in infiltration: up to 70%!

Macropores multiply the risk of leaching under (near)saturated conditions

Question 24

Leaching is increased by

Answer 24

• Solubility
• Low SOM
• Sandy soil
• Many macropores
• High rainfall periods?

Question 26

Why is the hydraulic conductivity higher in saturated soils, than in unsaturated soils?

Answer 26

When there is air in the soils (unsaturated), capillary forces are working on the water, slowing down its ability to move freely in the soil.