While potassium is not a constituent of any plant structures or
compounds, it plays a part in many important regulatory roles in the
plant. It is essential in nearly all processes needed to sustain
plant growth and reproduction.
Potassium plays a vital role in:
Photosynthesis
Translocation of photosynthates
Protein synthesis
Control of ionic balance
Regulation of plant stomata and water use
Activation of plant enzymes
It is known to activate at least sixty enzymes involved in plant
growth and this may be its most important function in the plant.
Plants deficient in potassium are less resistant to drought, excess
water, and high and low temperatures. They are also less resistant
to pests, diseases and nematode attacks. Potassium is also known as
the quality nutrient because of its important effects on quality
factors such as size, shape, color, taste, shelf life, fiber quality
and other quality measurements.
Potassium increases crop yields :
increases root growth and improves drought tolerance
builds cellulose and reduces lodging
helps translocate sugars and starches
aids in photosynthesis and food formation
produces grains rich in starch
increases protein content of plants
maintains turgor, reduces water loss and wilting
helps retard crop diseases and nematodes
Potassium Deficiency Symptoms
Plants absorb potassium as the potassium ion (K+). Potassium is a
highly mobile element in the plant and is translocated from the
older to younger tissue. Consequently, potassium deficiency
symptoms usually occur first on the lower leaves of the plant and
progress towards the top as the severity of the deficiency
increases. One of the most common signs of potassium deficiency is
the yellow scorching or firing (chlorosis) along the leaf margin.
In severe cases of potassium deficiency the fired margin of the
leaf may fall out. However, with broadleaf crops, such as soybeans
and cotton, the entire leaf may shed resulting in premature
defoliation of the crop. Potassium deficient crops grow slowly and have poorly developed
root systems. Stalks are weak and lodging of cereal crops such as
corn and small grain is common. Legumes are not strong competitors
for soil potassium and are often crowded out by grasses in a
grass-legume pasture. When potassium is not sufficient,
winter-killing of perennial crops such as alfalfa and grasses can
occur. Seeds from potassium deficient plants are small, shriveled, and
are more susceptible to diseases. Fruit is often lacking in normal
coloration and is low in sugar content. Vegetables and fruits
deteriorate rapidly when shipped and have a short shelf life in
the market.