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used by plants:
water status and activation of many enzymes
in photosynthesis and respiration
in the formation and translocation of sugars, proteins, starch, and
plant growth hormones
in stomata opening and closing
plants resistance to disease and improves winter hardiness
size (fruits are strong sinks for K), color, and acidity are related
positively to potassium concentrations
foliage range for apple leaves:
1.2% may mean K is limiting
trees and nonbearing trees have higher leaf K then mature cropping
trees. Levels strongly influenced by crop load, tending to be
higher with light crops and decreasing as crop load increases.
of leaf K for optimal crop quality is also dependent upon the nitrogen
status of leaves
ex. McIntosh 1.0-1.25 parts N to 1.0 part K are adequate
Delicious 1.25-1.5 N/K are adequate
Therefore, a Delicious sample that has 2.4% N should contain between
lbs/Ac/year which is equivalent to 150-210 lbs K2O.
lbs K are removed from orchard each year by crop.
value will also depend upon N status and variety. For example, for
varieties such as Delicious, ratios of 1.25 to 1.50 (N:K) appears to be
adequate. This translates
to the following, a Delicious sample containing 2.4% N should contain
between 1.6-2.0% K.
ppm or 0.4-0.6 meq/100 g soil (values based on the ammonium acetate
extraction method. If sodium bicarbonate method is used, values may be
< 150 ppm (< 0.4 meq/100 g soil)
250-800 ppm (< 0.6-2.0 meq/100 g soil)
> 800 ppm (> 2.0 meq/100 g soil)
soils low in K are rare. The relationship between soil tests, tissue tests and
response of fruit trees to K fertilizer has not been adequately
is strongly sorbed by soil components and thus is not readily mobile in
“Leaf analysis in conjunction with soil testing of samples
collected from both the topsoil and subsoil provides the best estimate
of the amounts of potassium that are available for uptake by fruit
trees.” (From Tree Fruit Nutrition book)
are visible when the concentration is below 0.75% of leaf dry weight.
Leaves containing 1% K do not show visible signs but fruit will
be smaller or poor color development occurs.
leaves are affected first. Leaf scorch will show up first. Undersides
of leaf margins may become darkened or browned (etching). Slow growth,
tip and marginal chlorosis/necrosis
advancing toward the midrib may also occur. Some species show a
recurving of petioles along with upward rolling of leaf blades.
Necrotic speckling and scorching of leaves is also common.
are slender and spurs are weak.
will be smaller, poorly colored and low in acidity (lacks flavor).
Fruit may hang on tree after leaf fall.
Trees may be more susceptible to winter injury and blossoms to
frost injury (also if high N/K ratio exists).
of fruit maturation is delayed.
risk of K deficiencies on:
problems/Interactions with other elements:
manganese, and calcium deficiencies become more pronounced with excess K.
levels of Ca can limit K uptake in some soils.
adequate soil supply of boron must also be maintained in order to
optimize the utilization of K (to support active root development for
updated: 14 February, 2001