Potassium is involved in maintaining the
water status of the plant and the
tugor pressure of
it's cells and the opening and closing of the stomata.
Potassium is required in the accumulation and
translocation of carbohydrates. Lack of potassium will
reduce yield and quality.
Potassium deficiency (K).
Older leaves are
initially chlorotic but soon develop dark necrotic
(dead tissue). First apparent on the tips
and margins of the leaves. Stem and branches may become
weak and easily broken, the plant may also stretch. The
plant will become susceptible to disease and toxicity.
In addition to appearing to look like iron deficiency,
the tips of the leaves curl and the edges burn and die.
Potassium - Too much sodium (Na) displaces K,
causing a K deficiency. Sources of high salinity are:
baking soda (sodium bicarbonate "pH-up"), too much
manure, and the use of water-softening filters (which
should not be used). If the problem is Na, flush the
soil. K can get locked up from too much Ca or ammonium
nitrogen, and possibly cold weather.