PLANTS DIG POTASSIUM
Potassium Forms
On fertilizer labels, potassium is represented as its oxide,
K2O, and is referred to as soluble potash because of the
test method used to determine its concentration levels.
In soil and hydroponic solutions, potassium exists as the
positively charged ion K+. In the ion form, potassium is
readily taken up by plant roots. Soil often contains high
levels of potassium as part of other soil mineral compounds, but it is generally in a form unavailable for
plant consumption.
There are a few forms of potassium found in
soil that are accessible to plants, including
readily available, slowly available or fixed
and exchangeable forms. Slowly available
and exchangeable forms of potassium are
found attached or stuck between negatively charged soil particles or colloids.
Available-soil potassium, as well as the
fertilizer, moves along with water through
the root zone and the potassium ions
are taken into plant roots when direct
contact is made.
Potassium in the Garden
“
Once potassium has entered a
plant, it behaves differently than
nitrogen and phosphorus in
84
Maximum Yield USA | October 2015
“
One of the most notable
jobs potassium has within
plants is its role in the
activation and manipulation
of plant enzymes.”
that it does not become a part of the plant’s organic
matter structures. Instead, it enters a vast array of
plant cells and is crucial in the activation and successful execution of numerous plant processes,
both chemical and physical.
One of the most notable jobs potassium has
within plants is its role in the activation and
manipulation of plant enzymes. Enzymes
act as a catalyst and help induce and
speed up the rate of chemical reactions
within plants. Potassium activates more
than 60 enzymes by helping to manipulate the shapes of enzyme molecules so
their active sites are accessible and ready
to work. Potassium can also neutralize negatively charged ions and other compounds
within the plant to stabilize its internal pH
between 7 and 8—the desired level for optimal enzyme activity. Adequate levels of potassium
within a plant’s cells help ensure a higher level of enzyme
activity at rates that support vigorous growth.
Potassium also plays a vital role in water and elemental
nutrient uptake, and the regulation of the stomata—
tiny, pore-like structures on the leaves and stems that
open and close to allow oxygen and water vapor to
exit plants, and carbon dioxide to enter. Stomata will
also stay closed during times of water scarcity to help
maintain proper water levels inside plants. The opening and closing of these structures is controlled by
specialized cells on their outer edges called guard cells.
Potassium is involved in regulating the function of
these cells. When potassium ions and water flood into
guard cells, the cells swell and the stomata open. As
potassium leaves the guard cells, the stomata will close
tightly to conserve water. When potassium levels are
low, the stomata will be slower to open or close, and will
have a harder time staying closed tight. Stomata that
stay closed tight help reduce water loss from plants,
and stomata that are more quick to open will allow
more carbon dioxide to enter the leaves, resulting in
increased rates of photosynthesis. Potassium also assists
in the translocation of sugars and starches.