8: Soil Colloids (8/9)

Question 1

Colloids

Answer 1

Small (<0.001mm) and highly reactive soil particles with electrically charged surfaces (mostly negative but some positively charged). Have an enormous surface area

Question 2

Hygroscopic water

Answer 2

Water held tightly by colloids in thin films that is not available for plants

Question 3

How does pore size affect capillary action?

Answer 3

The smaller the pores, the more capillary movement

Question 4

The three factors determining binding force of cations

Answer 4

1. Cation charge (valence)
2. Cation size (size of the hydrated radius)
3. Concentration of charge

Question 5

Cation charge impact on binding force

Answer 5

The stronger the charge (think Al3+ compared to Na+), the stronger the adsorption

Question 6

Size of cation (size of the hydrated radius) impact on binding force

Answer 6

Hydrated ions with smaller radii are more strongly attracted to colloids, larger radii have weaker attraction

Lyotropic series
Easier to replace to the right
Al3+ > Ca2+ > Mg2+ > K+ = NH4+ > Na+
K+ and NH4+ are equally easy to replace

Question 7

Concentration of cation impact on binding

Answer 7

If the concentration of a cation in soil solution is high, there is an increased tendency for that cation to be adsorbed

Question 8

Cation exchange importance

Answer 8

Reduces the nutrient losses from the soil