Potassium in soil

Question 1

Uptake of nutrients by crops

Answer 1

reaches highest around May and June

Question 2

plant availability of K

Answer 2

• amounts of K in different forms (clay mineralogy)

- accessibility to roots (movement of K and root systems)

Question 3

clay mineralogy

Answer 3

Illite region:
- non exchangeable K (slowly available)
Vermiculite region:
- exchangeable K and Ca = solution k+ and Ca2+ (readily available)

Question 4

mass flow of nutrient movement through soils to roots

Answer 4

• water flow sweeps ions towards root

- rate = water flow rate x ion concentration in sol solution

Question 5

diffusion of nutrient movement through soils to roots

Answer 5

• depletion of ions in rhizoshpere

- concentration gradient drives diffusion: Q=A.k.dC/dx

Question 6

Solutions to the immobility problem, ways to extend the depletion zone

Answer 6

• root extension
• root hairs
• branching
• mycorrhizae

Question 7

K buffering

Answer 7

• the ability of the soil to prevent large changes in solution concentration of K when K is added or removed from the soil
• it allows plants to survive on very low concentrations of K in soil solution
• when K is taken up from solution, the concentration in solution changed by only a small amount since it is buffered by the large excess of exchangeable K

Question 8

Extractable K (ADAS)

Answer 8

estimating K availability in soils:

• represents exchangeable pool
• considered to rate (index) soil in order of K availability rather than to measure the amount available to a crop

Question 9

Data from K absorption isotherms

Answer 9

estimating K availability in soils:

• K n soil solution
• exchangeable K
• buffer power