Potassium Cycle

Primary Sources

Micas & Potassium Feldspars

Weathering Process

 Mineral lattices break down → K becomes available

Stages of K release

1. Slowly available K at mineral edges (Non-exchangeable)

2. Readily exchangeable K and K in soil solution → taken up by roots. 

Plant Uptake

Plants absorb large amounts of K.

Return to Soil

• Throughfall (rain washing leaves)
  

• Plant residues
  

• Animal wastes (mainly urine)

Losses

• Erosion and runoff

• Leaching to groundwater

Agroecosystems

20–100% of plant K exported

Major Forms K is in

• primary minerals

• nonexchangeable form

Low K Soils / High Biomass Removal

Exchangeable/solution K:

• insufficient.
  

Supplementation needed:

• Fertilizers

• Poultry Manure

• Wood Ashes

Natural K Replenishment

• Perennial Vegetation

• Natural Ecosystems

• Agricultural Systems

Perennial Vegetation

Forests and pastures 

• restore soil K

Perennial Vegetation (Deep Roots)

• Absorb K from subsoil
  

• Transport to leaves
  

• Return to soil (via leaf fall and leaching)

Natural Ecosystems

Small annual K losses (1–5 kg/ha)

• offset by weathering of minerals

• translocation to soil surface.

Agricultural Systems

Higher leaching losses

• fertilizer-supplied K

• seasonal crop rooting