Teaching Organic Farming and Gardening

Soil Chemistry and Fertility

24 | Unit 2.2

5. potassium (K)

a) physiological role in plant development

potassium is essential for the movement of sugars within the plant and for starch formation.
It is necessary for the opening and closing of stomata by guard cells, controlling water use
by the plant. It encourages root growth and helps build disease resistance. It is involved with
photosynthesis and enzyme activity. It helps regulate metabolic activity and is involved in
protein synthesis. potassium promotes larger and better-quality fruits and grains. In some plants,
more potassium is required than any other nutrient.

b) Soil nutrient deficiencies, imbalances, toxicity

potassium deficiency symptoms include:

• Slow growth

• Tip and marginal “burn” starting on more mature leaves. As severity of the deficiency

increases, this condition progresses toward the top of the plant.

• Weak stalks, plants lodge easily

• Small fruit or shriveled fruit and seeds

• Reduced disease and pest resistance

• Increased sensitivity to drought, frost, and salts

• White or yellow spots develop along the edges of clover leaves, in severe cases these

join to give a scorched appearance.

excess potassium can cause:

• Magnesium deficiency

• Calcium deficiency in acid soils

c) the potassium cycle (see Figure 5)

figUre 5. the pOtASSIUm CyCLe
(FROm WWW.AGCentRAL.COm/ImCDemO/07pOtASSIUm/07-06.htm)

Students’ Lecture Outline

K+K+

K+ K+ K+

K+ K+ K+ K+ K+

K+ K+ K+ K+ K+

K+ K+

K+ K+

K+

Soil Rocks

and

Minerals

Soil Colloid

Soil Colloid

Trapped K+

Unavailable

Slowly Available

Soil Colloid

Soil Water

Readily

Available