Page 8 - AWA Vol. 37-5 issue

CROP PROTECTION

ROLE OF POTASSIUM IN PLANT

GROWTH AND DEVELOPMENT

Potassium is not a structural compo- glucose from the leaves, where it is
nent of plant cells and tissues. How- synthesised by photosynthesis, to so
ever, potassium is by far the most im- FDOOHG oVLQN VLWHV VXFK DV VHHGV URRW
SRUWDQW oIDFLOLWDWRUp QXWULHQW UHTXLUHG IRU tubers and bulbs for storage as starch
DR. TERRY MABBETT synthesis of amino acids and proteins and other insoluble carbohydrates
from ammonium ions, and essential for (polysaccharides).
Potassium (K) is one the three macro- HIÞFLHQF\ RI WKH FKHPLFDO UHDFWLRQV UH- This crucial control role in plant
nutrients required for rapid, balanced sponsible for the production of glucose physiology has led to potassium be-
and sustainable plant growth and de- by photosynthesis in the chlorophyll LQJ FDOOHG oWKH JDWHNHHSHUp QXWULHQW
velopment. Together with nitrogen containing cells of leaves and stems as a key player in water uptake, water
(N) and phosphorous (P), potassium in green plants. transport and its movement around the
accounts for the major proportion of plant and conservation (accumulations
fertiliser spread and watered onto the and storage in cell vacuoles). As such
ZRUOGpV DJULFXOWXUDO ODQG potassium is crucial to maintenance of
Mainstream potassium fertilisers are good water relations and plant turgor
mined from underground deposits of and avoidance of water stress and
VDOWV RUH 7KH\ DUH wilting.
• Muriate of potash which is the Balance is the key word in the world
common name for potassium chlo- of fertilisers, nutrients, plant nutrition
ride (KCl), and which contains 60 per and water relations. The context in
cent K2O*. Manufacture of this type ZKLFK oEDODQFHp LV XVHG UHODWHV WR WKH
of fertiliser as a granule formulation interaction between different nutrients
gas gone a long way to boost storage and the fact that individual nutrients
RI WKH SURGXFW DQG HIÞFLHQW DSSOLFD- DUH UHTXLUHG LQ VSHFLÞF DPRXQWV DW SDU-
tion to crops. WLFXODU VWDJHV RI D FURS SODQWpV JURZWK
s 6XOSKDWH RI SRWDVK SRWDVVLXP and development cycle. As such an
VXOSKDWH . 62 ZKLFK LV PDQXIDF- imbalance in the fertiliser programme
tured from the muriate of potash, by invariably leads to an imbalance in
chemical processing, to contain 48-50 growth and development, failure to
per cent by weight (w/w) of K2O*. Banana fruit provide a particularly achieve full potential yield and loss of
crop. More than most other nutrients,
• Kainit which is a mixture of po- rich supply of potassium. Vegetable
tassium and sodium salts with a (cooking) bananas shown here potassium illustrates the importance of
nutrient interaction, interdependence
K2O* content ranging from 14-30 (Dr Terry Mabbett)
and balance.
per cent w/w. Kainit contains sub-
stantial amounts of magnesium and In addition, potassium plays a key Indeed it would be peculiar if potassi-
is especially valuable for root crops role in the transport of other molecules um which is so crucial to the metabolic
like sugar beet. and ions across cell membranes. This processes of photosynthesis and pro-
means that potassium is intimately in- tein synthesis, in which nitrogen and
volved in osmosis, which is the move-
ment of water and other small particles
across the selectively permeable cell
membranes. These membranes are the
plasmalemma (the plasma membrane)
which is the outer membrane bounding
the living plant cell, and the tonoplast
which separates the living cell contents
from the centrally placed cell vacuole
(space).
Osmosis is a physiological process
Potato (Solanum tuberosum) in the
DW WKH YHU\ FHQWUH RI
plant family Solanaceae has a high
requirement for potassium (Picture • absorption of water by roots from
courtesy Dr Roderick Robinson) the soil,
• water movement through cells
[* K2O (potassium oxide) is used as and tissues,
the standard measure of the potassium • water conservation and its use to
content of a fertiliser raw material or produce turgor (hydrostatic pressure)
Tomato is another crop belonging to
SURGXFW 6LPLODUO\ 1 DQG 3 2 DUH XVHG and essential to prevent wilting in
the plant family Solanaceae which
as standard measures for, respectively, non-woody plants
has a high requirement for potassium
the nitrogen and phosphorous contents • the movement of soluble food (Picture Dr Terry Mabbett)
of a fertiliser raw material or product.] from one tissue to another – e.g.
6 Vol. 37 No. 5