Chapter 12
Plant K nutrition and K fertilizers
Plant K
A,Potassium content of plants
1,20-50 g kg-1
2,Plants take up a large amount of K,Only N
is taken up more.
3,In some plants (sugar beets and potatoes)
K uptake is greater than N uptake
1,Diffusion of K to plant roots accounts
for
>75% of plant uptake,The diffusion
distance is very small.
2,K dissolved in soil water can also
reach the
plant root by mass flow.
B,Potassium movement to roots
Plant K
c,Potassium movement in the plant
1,Mobile in the plant,Translocated from
older leaves to young growing points.
2,The concentration of K in the phloem sap
is high,The sap can be translocated for
relatively long distances in the plant,
either upward or downward.
Plant K
D,Form of potassium in plants
1,K+ remains in its ionic form in the
plant (remains as K+).
2,K+ may also be bound to negative
charges on the surface of plant
tissue,
Plant K
Function of potassium in plants
1,Activation of enzymes
The main function of K+ in biochemistry is its
activation of various enzyme system.
a) Starch synthesis; b) ATP production;
c) Photosynthesis (Rubisco); d) Protein
synthesis
In vitro experiments have shown that maximum
K+ activation is obtained within a
concentration rang of 40 to 80 mol/m3.
K+ can bring about conformational changes of
enzymes,
Effects of K+ on the incorporation of 15N into grains
proteins of wheat (se?er 1980)
K 1 ( 0, 3 mM i n t h e me d i u m) K 2 ( 1, 0 mM i n t h e me d i u m)
A l b u m i n ( 清 蛋白 ),mg
15
N / k g 42,4 6 7, 0
G l o b u l i n （ 球 蛋白 ）,mg
15
N / k g 3 6, 4 4 9, 2
P r o l a mi n （ 谷 醇 溶 蛋白 ）,mg
15
N / k g 108,0 1 5 1, 0
G l u t e l i n （ 谷 蛋白 ）,mg
15
N / k g 1 3 0, 0 1 9 4, 0
K - c o n c e n t r a t i o n mg K / D M 4, 9 5, 0
Polypeptide synthesis in the ribosomes requires
high K+ concentration(40-50mM)
and K+ is essential for protein synthesis
K increases the N efficiency
Function of potassium in plants
2,Water regime(水分状况 )
a) K controls cell water potential and
osmosis
(1) A large concentration of potassium in the
cell sap creates conditions that cause
water to move into the cell (osmosis)
through the porous cell wall and
membrane,This process is related to
the movement of nutrients and sugars
throughout the plant.
K regulate the stoma open and
close
Function of potassium in plants
b) Cell turgor
(1) The term ―turgid‖ is used to describe plant cells
that are full of water,This helps plants stand
upright,even without the woody tissues that
trees have.
(2) Special cells (called guard cells) in the leaf
control the size of the stomatal opening that
allows CO2 to move into the leaf and water to
move out (transpiration),The amount of K+ in
these guard ells controls their opening and closing.
c) Water uptake by roots
3,Meristematic growth
a) H+ is pumped into the apoplast
(outside the cell wall),The H+ weakens
the cell wall allowing for expansion,In
order for H+ to be pumped out of the cell,
K+ must be pumped in,
Function of potassium in plants
Function of potassium in plants
4,K and stress resistance
a) Drought tolerance
(1) Through control of both water loss
throughtranspiration and water absorption by
roots
b) Winter hardiness
c) Fungal disease resistance (powdery mildew白
粉病, brown spot（ 褐斑病 ）,brown rust褐锈病 ）
d) Tolerance to insect feeding
e) Reduced stalk rot and lodging
Stronger stems
Function of potassium in plants
5,Photosynthesis and translocation of photosynthates
K stimulates the photosynthetic O2 production which
means it has a promoting impact on the e- flux through the
photosynthetic e- transport chain and therefore also on the
reduction of NADP+ and the generation of ATP.
K+ promoted the de novo synthesis of the enzyme
ribulose bisphosphate caboxylase (Rubisco); decreased the
diffusive resistance for CO2 in the mesophyll(叶肉 ）,
High K+ concentration (100mol/m3) in the outer
medium induced a broader pH optimum for the enzyme
RuBP carboxylase as compared with low K(10mol/m3)
Effects of K+ on the CO2 assimilation,
photorespiration and dark respiration (People and
koch 1979)K
+
i n l e a v e s mg
K
+
/g DM
C O 2 - a s s i mi l a t i o n
M g dm
- 2
h
- 1
P h o t o r e s p i r a t i o n
D p m dm
- 2
h
- 1
D a r k r e s p i r a t i o n
M g dm
- 2
h
- 1
1 2, 8 1 1, 9 4, 0 0 7, 5 6
1 9, 8 2 1, 7 5, 8 7 3, 3 4
3 8, 4 3 4, 0 8, 9 6 3, 0 6
Increasing CO2 assimilation was paralleled by an increase in
photorespiration and a decrease in the dark respiration.
? Photosynthates translocation
? Numerous authors have shown that K+ enhances the
translocation of photosynthates.
? K+ promotes phloem transport,and is probably related
to the beneficial effect on phloem loading.
? According to Lang(1983) higher K+ uptake by the
sieve tube-companion cell complex(筛管伴胞复合体 )
induces osmotic water flow into the complex to,push”
the phloem mass flow,
? Release of K+ from the phloem tissue on the other hand
leads to water release and thus contributes to the,pull
mechanism”
Function of potassium in plants
In storage sinks such as the sugar beet taproot
and in sugarcane,sugar is stored at high
concentrations in the vacuole,Where a K
concentration around 100mol/m3 is required for
efficient sucrose uptake into the vacuole.
Potassium nutrition favors the storage of starch,
sugars and proteins as observed in numerous crops.
Apart from favoring photosynthesis efficiency and
phloem loading K+ may have also direct impact on the
storage.
So,K has also been related to fruit quality and to
the oil content of some seeds.
Function of potassium in plants
Replacement of potassium by sodium
? The question of whether Na+ can
replace K+ in physiological processes
in the plant is not only of academic
interest but also of practical
importance in relation to fertilizer
usage.
? The beneficial effects of Na+ on plant
growth are particularly observable
when the K+ supply is inadequate,
Effect of increasing potassium concentrations in the grain
yield of rice,in the presence or absence of a high Na level
in the nutrient solution (Yoshida and Castaneda 1969)
G r a i n yi e l d,g/ pot K c onc e nt r a t i on
M ol / m
3
- Na + 43m ol / m
3
N a
0,0 25 4,6 1 1,0
0,050 6,9 19,9
0,125 26,4 46,6
0,250 63,3 67,3
1,25 67,5 75,9
2,50 90,8 87,6
5,00 103, 6 92,6
Effect of the Na+/K+ in the nutrient solution on the growth of
sugar beet leaves and storage root (Lindhauer 1989)
N u t r i e n t s o l u t i o n,m o l m
3
4, 5 K
+
,0, 5 N a
+
0, 5 K
+
,4, 5 N a
+
0, 5 K
+
,0, 5 N a
+
L e a v e s,g DM 5 0, 3 6 5, 2 5 8, o
R o o t s,g D M 107 83 81
The beneficial effect of Na+ on leaf growth
but not on the growth of storage root.
Response to sodium differ between genotypes.
notice
? In less specific processes such as raising
cell turgor some replacement is possible.
? For the ―high and medium Na+ uptake
potential species‖,the favorable effect of
Na+ is important on plant growth,This is
particularly the case for the Beta
species(甜菜 ),In these species Na+
contributes to the osmotic potential of cell
and thus has a positive effect on the water
regime of plants.
Uptake potential of various crops for sodium (Marshner
1971)
hi gh m e di um l ow V e r y l ow
F odd e r be e t （ 饲用 甜菜 ） C a bba ge B a r l e y B uc kw he a t （ 荞麦 ）
S uga r be e t （ 糖用 甜菜 ） C oc onu t F l a x ( 亚麻 ) M a i z e
M a ngo l d （ 甜菜 ） C ot t on M i l l e t R ye
S pi na c h （ 菠菜 ） L upi ns R a pe S oya
S w i s s c ha r d （ 叶 用 甜菜 ） O a t s w he a t S w e de （ 芜箐 甘蓝 ）
T a bl e be e t （ 食用 甜菜 ） pot a t o
R ubb e r
T ur ni ps ( 芜 箐 )
Potassium deficiency symptoms
1,When K+ is slightly deficient,there may be no
obvious symptoms,but plant growth will be reduced
(hidden hungry),
2,At higher levels of K+ deficiency there will be
chlorosis (yellowing黄化 ) or necrosis (dying tissue坏
死 ) on the leaf tips and leaf edge.
Because K is a mobile nutrient,K deficiency will
first appear on lower leaves (maize,cereals,fruit trees),
but in some species such as clover irregularly
distributed necrotic spots occur on the leaves.
Potassium deficiency symptoms
For corn,the margins of the lower
leaves turn brown,This development of
dead tissue is accompanied by a striped
appearance in the remainder of the leaf.
The entire leaf has a very distinct light
green appearance when viewed from a
distance.
The striping associated with K
deficiency in corn can be easily confused
with deficiency symptoms for sulfur (S),
magnesium (Mg),and zinc (Zn).
Potassium deficiency symptoms
The margins of the leaflets turn
light green to yellow when K is
deficient for soybean production,As
with corn,these deficiency symptoms
first appear on the lower leaves,With
maturity,the deficiency symptoms
expand to leaves closer to the top of
the canopy
Potassium Deficiency in Soybeans
Potassium deficiency symptoms
Potassium deficiency in alfalfa
is characterized by yellow or white
spots on the margins of the leaflets,
with symptoms first appearing on
the older plant tissue,This could be
confused with insect damage,
Potassium Deficiency in Alfalfa
K deficiency of Maize
K deficiency of Apple trees
Bluish green,with
slight marginal and
intervenal chlorosis,
followed by marginal
scorching（烧焦，枯
萎）,either brown or
grayish brown color.
? K deficiency of
citrus trees,older
leaves die and fall
off,kraurosis of
younger leaves from
tip and margins
? The deficient plant on the left has yellow scorched
older leaves,which dry and papery,The plant on the
right is healthy,Yellowing and scorching of the older
leaves begins at the edges (left and centre) and
eventually spread between the main veins towards
the centre and leaf(right)
? Fruit fails to expand at the stem end.
Potassium deficiency symptoms
３, K+ deficiency may also be evident in the
form of increased lodging,winter injury,
drought stress,or reduced disease or insect
resistance.
4,Abnormal development of tissues (such as
cambium形成层, cuticle角质层 ） and cell
organelles (such as chloroplast and
mitochondria) is observed in k+ deficient
plants.
Relationships of grain yields and k
concentration in the sap of cereal leaf
Excessive levels of potassium
1,K+ is not directly toxic to plants
or other organisms.
2,High soil K can inhibit uptake of
other cations,such as Ca
deficiency
3,K can counteract problems of excess N
a) N stimulates vegetative growth that
may lead to
lodging or disease or insect
susceptibility.
b) K has the opposite effect
Excessive levels of potassium
Soil Potassium
Total K in the Soil
1,The total K content in the soil
ranges between 0.3-2.5%,The
textbook mentions some clay soils
may have more than 4% K.
2,the greatest part of K is bound in
primary minerals and in the
secondary clay minerals (such as
illites伊利石 and chlorite绿泥石 ).
Forms of K in the soil
1,Solution K (Dissolved K+ ions)
a) 1-10 mg/L
b) Solution K is very low compared to
crop
requirements
c) Plants are very efficient at extracting
K to very
low solution levels
Potassium concentration of some primary and
secondary clay minerals (Scheffer and
Schachtschabel 1982)
Biotite,50-400mmol/m3; musicovite,2.5mmol/m3
M i n e r a l s K c onc e nt r a t i on i n g/ kg
Al k a l i f e l ds pa r s 钾 长石 32 - 120
Ca - N a f e l ds pa r s 钙 - 钠 长石 0 - 24
M us c ovi t e ( K m i c a ) 白 云母 60 - 90
B i ot i t e ( M g m i c a ) 黑云母 36 - 80
I l l i t e 伊利石 32 - 56
V e r m i c ul i t e 蛭石 0 - 16
C hl or i t e 绿泥石 0 - 8
M ont m or i l l oni t e 蒙脱石 0 - 4
Forms of K in the Soil
2,Exchangeable K
a) Weakly sorbed on the surfaces of clay or organic
matter.
b) K may typically occupies 2 to 5% of the cation
exchange sites in a soil.
c) The term,exchangeable” means that the K sorbed
to the clay or organic matter surfaces can be
replaced by other positively charged cations from
the soil solution.
d) This form of K can replace the K taken up from the
soil solution.
3,Non-exchangeable K
a) Also called ―fixed K‖
b) It is held within the clay layers by
strong
bonds
c) It is inaccessible (not accessible) to
plant roots
d) It may take many years for this form
of K to become available to the plant.
Forms of K in the Soil
P-position
E-position
i-position
Gapon efficients (K+/Mg2+),
P-position,2.21 (mol/m3)-1/2 ;e-position(mol/m3)-1/2,102;i-position infinite
Forms of K in the soil
4,Mineral K
a) Contained in rocks such as feldspar
(KAlSi3O8)
and mica
b) The release of K from these rocks is
very,very
slow.
K fractions of a sandy loam and a loamy sand soil
(Martin and Sparks 1983) E x c h a n g e K +
( C a C I 2 )
N o n e x c h a n g e K
+
( H NO 3 )
M i n e r a l K
+
T o t a l K
+
I n mol K k g
- 1
s o i l
S a n d y l o a m 1, 7 2 2, 2 0 3 7, 6 4 1, 5
L o a my s a n d 1, 1 5 2, 0 9 3 1, 3 3 4, 5
The K in the solution and exchange K are called ―easily available K‖
Nonexchange K+ is called as ―slowly releasing potassium
or slowly available K‖
Forms of K in the soil
5,Plant available K includes both
solution K and exchangeable K
6,K is not bound in organic forms like
N and P,It is quickly leached out of
crop residues and roots when the
plant dies.
Potassium transformations in the soil
1,Clay Fixation and Release
１ ) Clay fixation refers to the process by
which K is trapped between layers of
clay.
２ ) It is temporarily unavailable for plant
use,
３ ） Clay fixation and release is affected by soil
factors such as:
a) Soil water – if the soil is very dry the
clay layers squeeze together and the K is
trapped,If the soil is wet,the clay layers
are forced apart and some K is released.
(very slowly)
(b) H+and NH4+ – can compete with K+ for
K+ fixing binding site,as pH increases,
there are fewer H+ ions on the exchange
sites,and more K+ is bound;
(c) CEC – as CEC goes up,more K+ is
bound
Potassium transformations in the soil
d) Fixing power of the 2:1clay minerals
Older vermiculite>illite>smectite (蒙皂石 ）
>kaolinite
e) Soils with high K-fixing capacities show
little response to large amounts of K
fertilizer because the surplus of available
K quickly binds to clays,On the other
hand,these soils are generally able to
meet crop needs,because they already
have a large amount of K in storage.
Potassium transformations in the soil
Potassium transformations in the soil
2,Cation exchange (Sorption and desorption)
a) K+ sorbs to (sticks to) the negative surface
of clay due to weak electrostatic attraction.
b) When solution K+ is depleted (goes down),
the K+ desorbs from the soil and enters the
soil solution.
3,Competition with other cations
4,Weathering
Affected by factors such as
temperature and moisture
Potassium transformations in the soil
Potassium availability
1,Readily available
a) Labile K
b) Soil solution and exchangeable K
c) < 2% of total K in soil
2,Slowly available or less readily
available
a) Non-exchangeable,fixed K
b) 1-10% of total K in soil
3,Unavailable or mineral
a) K contained in primary soil minerals
b) 90-98% of the K in the soil
Potassium availability
Soil Solution
K+
Primary
Minerals
KRelease
SorptionDesorptionWeathering
Potassium availability
1,Leaching – leaching is affected by the
concentration of K+ in the soil
solution and the amount of water
moving through the soil,Because K+
in the soil solution is very low,
leaching losses of K are generally low,
The loss of K to leaching is only a
problem where rainfall is very high or
under irrigated conditions,
Potassium loss from soil
2,Erosion removes the surface soil
where plant available K+ is highest.
Reducing erosion can maximize
the amount of K+available for
crops.
Potassium loss from soil
Potassium fertilizer
Potassium chloride (muriate of potash)
1,KCl
2,0-0-60
3,90% of all K fertilizer used in the
U.S,is KCl,It is economical.
4,Varies in color from pink to white
depending on the mining and
recovery process
5,Can be directly applied or blended
with other fertilizers.
6,Cl may increase yields of some
crops and also increase disease
resistance in some small grains
7,Some lower grade fertilizer
types(33-%-41%K),which contain
substantial amount of NaCI and are
therefore suited to natrophilic crops
(sugar beet,cabbage,oats)
Potassium chloride (muriate of potash)
Potassium sulfate (sulfate of potash)
1,K2SO4
2,0-0-50
3,About 5% of the K fertilizer used
in the US is K2SO4
Potassium sulfate (sulfate of potash)
4,Primarily used for crops such as
tobacco,potatoes,and a few
vegetable crops that are
negatively affected by Cl from
KCl fertilizer.
5,May also be used when S is
required,
Potassium nitrate (nitrate of potash)
1,KNO3 – provides both N and K
2,13-0-45
3,Too expensive for common use,In
the U.S.,it is primarily use for
horticultural and greenhouse crops
such as celery,tomatoes,potatoes,
leafy vegetables,and a few fruit
crops.
Potassium magnesium sulfate
1,K2SO4 + 2 MgSO4
2,0-0-22-22S
3,Primarily produced from mines in
Germany and France,It is used as
a source of Mg and S.
4,Applied directly or blended with
other fertilizers
Plant ash and flue ash
Plant ash K2CO3(K2SO4 and KCI)
0-0-0.67~35.4
Avoid from leaching in the storage.
Applied in all crops and soil apart from
saline soil
Flue Ash K2SiO4
k2O,8%~40%
only used as basal,topdress or
siderdress,but not for pop-up.
C o t t o n s e e d h u l l a s h 0 — 2 7, 0 — — — —
C o t t o n s e e d m e a l 6 t o 7 2, 5 1, 5 0, 4 0, 9 0, 2 —
S w e e t p o t a t o s k i n s b o i l e d
( a s h ) — 3, 2 9 1 3, 9 — — — —
S w e e t p o t a t o e s 0, 2 0, 1 0, 5 — — — —
T a n k a g e 7, 0 1, 5 3 t o 1 0 — — — —
T e x t i l e s l u d g e s 2, 8 2, 1 0, 2 0, 5 0, 2 — —
W o o d a s h e s 0, 0 2, 0 6, 0 20,0 1, 0 — —
Fl y a s h,
c o a l
w o o d
0, 3
0, 1
—
0, 6
0, 1
1 0, 0
0, 4 8
9, 8
—
0, 6 6
—
—
—
—
G r a p e s k in s ( a s h ) — 3, 6 3 1, 0 — — — —
? A,Some crops are sensitive to high
amounts of chloride,This chlorophobic
species(忌氯作物） include tobacco,
grapes,fruit trees,sugar cane,potatoes,
strawberries,cucumber and onions,It
is preferential to treat these crops with
potassium sulphate.
?
Management of K fertilizer
Effect of a varying chloride/sulphate on grope yield
(Edelbauer 1978)
N u t r i e n t s o l u t i o n
K C I,me / L K 2 SO 4,me / L
G r a p e y i e l d
g / p o t
W e i g h t o f c l u s t e r
g
N o, o f
c l u s t e r / p o t
4, 0 0 111 5 8, 9 1, 8 9
2, 5 1, 5 149 7 0, 5 2, 1 0
1,0 3, 0 252 8 4, 2 3, 0 0
0 4, 0 254 9 1, 3 2, 7 8
? Most field crops are not sensitive
to chloride and are generally
treated with muriate,Oil palms
and coconut even appear to have a
chloride requirement.
? Potassium nitrate is mainly used
for spraying on leaves of fruit trees
and horticultural crops
Management of K fertilizer
B,K uptake in plants is affected by
soil water,aeration,temperature,
and tillage.
C,Use small,frequent applications
on soils with high K fixation
capacity and high leaching.
Management of K fertilizer
1,Surface application
a) K has limited mobility in the soil
b) Surface-applied K will move to roots
very slowly
2,Broadcast and incorporate
a) Places K in root zone
b) Maximizes K fixation on fine-textured
soils with high fixation potential
Fertilizer placement
3,Band placement
a) Minimizes contact between soil and
fertilizer
b) Can reduce K fixation
c) Most beneficial on low K soils with
high fixation capacity
Fertilizer placement
Deficient soils
? Potassium deficiency occurs
commonly on a number of different
soil types.
? Light sandy acid soil
? Organic soil
? Heavily cropped soil
Plant K nutrition and K fertilizers
Plant K
A,Potassium content of plants
1,20-50 g kg-1
2,Plants take up a large amount of K,Only N
is taken up more.
3,In some plants (sugar beets and potatoes)
K uptake is greater than N uptake
1,Diffusion of K to plant roots accounts
for
>75% of plant uptake,The diffusion
distance is very small.
2,K dissolved in soil water can also
reach the
plant root by mass flow.
B,Potassium movement to roots
Plant K
c,Potassium movement in the plant
1,Mobile in the plant,Translocated from
older leaves to young growing points.
2,The concentration of K in the phloem sap
is high,The sap can be translocated for
relatively long distances in the plant,
either upward or downward.
Plant K
D,Form of potassium in plants
1,K+ remains in its ionic form in the
plant (remains as K+).
2,K+ may also be bound to negative
charges on the surface of plant
tissue,
Plant K
Function of potassium in plants
1,Activation of enzymes
The main function of K+ in biochemistry is its
activation of various enzyme system.
a) Starch synthesis; b) ATP production;
c) Photosynthesis (Rubisco); d) Protein
synthesis
In vitro experiments have shown that maximum
K+ activation is obtained within a
concentration rang of 40 to 80 mol/m3.
K+ can bring about conformational changes of
enzymes,
Effects of K+ on the incorporation of 15N into grains
proteins of wheat (se?er 1980)
K 1 ( 0, 3 mM i n t h e me d i u m) K 2 ( 1, 0 mM i n t h e me d i u m)
A l b u m i n ( 清 蛋白 ),mg
15
N / k g 42,4 6 7, 0
G l o b u l i n （ 球 蛋白 ）,mg
15
N / k g 3 6, 4 4 9, 2
P r o l a mi n （ 谷 醇 溶 蛋白 ）,mg
15
N / k g 108,0 1 5 1, 0
G l u t e l i n （ 谷 蛋白 ）,mg
15
N / k g 1 3 0, 0 1 9 4, 0
K - c o n c e n t r a t i o n mg K / D M 4, 9 5, 0
Polypeptide synthesis in the ribosomes requires
high K+ concentration(40-50mM)
and K+ is essential for protein synthesis
K increases the N efficiency
Function of potassium in plants
2,Water regime(水分状况 )
a) K controls cell water potential and
osmosis
(1) A large concentration of potassium in the
cell sap creates conditions that cause
water to move into the cell (osmosis)
through the porous cell wall and
membrane,This process is related to
the movement of nutrients and sugars
throughout the plant.
K regulate the stoma open and
close
Function of potassium in plants
b) Cell turgor
(1) The term ―turgid‖ is used to describe plant cells
that are full of water,This helps plants stand
upright,even without the woody tissues that
trees have.
(2) Special cells (called guard cells) in the leaf
control the size of the stomatal opening that
allows CO2 to move into the leaf and water to
move out (transpiration),The amount of K+ in
these guard ells controls their opening and closing.
c) Water uptake by roots
3,Meristematic growth
a) H+ is pumped into the apoplast
(outside the cell wall),The H+ weakens
the cell wall allowing for expansion,In
order for H+ to be pumped out of the cell,
K+ must be pumped in,
Function of potassium in plants
Function of potassium in plants
4,K and stress resistance
a) Drought tolerance
(1) Through control of both water loss
throughtranspiration and water absorption by
roots
b) Winter hardiness
c) Fungal disease resistance (powdery mildew白
粉病, brown spot（ 褐斑病 ）,brown rust褐锈病 ）
d) Tolerance to insect feeding
e) Reduced stalk rot and lodging
Stronger stems
Function of potassium in plants
5,Photosynthesis and translocation of photosynthates
K stimulates the photosynthetic O2 production which
means it has a promoting impact on the e- flux through the
photosynthetic e- transport chain and therefore also on the
reduction of NADP+ and the generation of ATP.
K+ promoted the de novo synthesis of the enzyme
ribulose bisphosphate caboxylase (Rubisco); decreased the
diffusive resistance for CO2 in the mesophyll(叶肉 ）,
High K+ concentration (100mol/m3) in the outer
medium induced a broader pH optimum for the enzyme
RuBP carboxylase as compared with low K(10mol/m3)
Effects of K+ on the CO2 assimilation,
photorespiration and dark respiration (People and
koch 1979)K
+
i n l e a v e s mg
K
+
/g DM
C O 2 - a s s i mi l a t i o n
M g dm
- 2
h
- 1
P h o t o r e s p i r a t i o n
D p m dm
- 2
h
- 1
D a r k r e s p i r a t i o n
M g dm
- 2
h
- 1
1 2, 8 1 1, 9 4, 0 0 7, 5 6
1 9, 8 2 1, 7 5, 8 7 3, 3 4
3 8, 4 3 4, 0 8, 9 6 3, 0 6
Increasing CO2 assimilation was paralleled by an increase in
photorespiration and a decrease in the dark respiration.
? Photosynthates translocation
? Numerous authors have shown that K+ enhances the
translocation of photosynthates.
? K+ promotes phloem transport,and is probably related
to the beneficial effect on phloem loading.
? According to Lang(1983) higher K+ uptake by the
sieve tube-companion cell complex(筛管伴胞复合体 )
induces osmotic water flow into the complex to,push”
the phloem mass flow,
? Release of K+ from the phloem tissue on the other hand
leads to water release and thus contributes to the,pull
mechanism”
Function of potassium in plants
In storage sinks such as the sugar beet taproot
and in sugarcane,sugar is stored at high
concentrations in the vacuole,Where a K
concentration around 100mol/m3 is required for
efficient sucrose uptake into the vacuole.
Potassium nutrition favors the storage of starch,
sugars and proteins as observed in numerous crops.
Apart from favoring photosynthesis efficiency and
phloem loading K+ may have also direct impact on the
storage.
So,K has also been related to fruit quality and to
the oil content of some seeds.
Function of potassium in plants
Replacement of potassium by sodium
? The question of whether Na+ can
replace K+ in physiological processes
in the plant is not only of academic
interest but also of practical
importance in relation to fertilizer
usage.
? The beneficial effects of Na+ on plant
growth are particularly observable
when the K+ supply is inadequate,
Effect of increasing potassium concentrations in the grain
yield of rice,in the presence or absence of a high Na level
in the nutrient solution (Yoshida and Castaneda 1969)
G r a i n yi e l d,g/ pot K c onc e nt r a t i on
M ol / m
3
- Na + 43m ol / m
3
N a
0,0 25 4,6 1 1,0
0,050 6,9 19,9
0,125 26,4 46,6
0,250 63,3 67,3
1,25 67,5 75,9
2,50 90,8 87,6
5,00 103, 6 92,6
Effect of the Na+/K+ in the nutrient solution on the growth of
sugar beet leaves and storage root (Lindhauer 1989)
N u t r i e n t s o l u t i o n,m o l m
3
4, 5 K
+
,0, 5 N a
+
0, 5 K
+
,4, 5 N a
+
0, 5 K
+
,0, 5 N a
+
L e a v e s,g DM 5 0, 3 6 5, 2 5 8, o
R o o t s,g D M 107 83 81
The beneficial effect of Na+ on leaf growth
but not on the growth of storage root.
Response to sodium differ between genotypes.
notice
? In less specific processes such as raising
cell turgor some replacement is possible.
? For the ―high and medium Na+ uptake
potential species‖,the favorable effect of
Na+ is important on plant growth,This is
particularly the case for the Beta
species(甜菜 ),In these species Na+
contributes to the osmotic potential of cell
and thus has a positive effect on the water
regime of plants.
Uptake potential of various crops for sodium (Marshner
1971)
hi gh m e di um l ow V e r y l ow
F odd e r be e t （ 饲用 甜菜 ） C a bba ge B a r l e y B uc kw he a t （ 荞麦 ）
S uga r be e t （ 糖用 甜菜 ） C oc onu t F l a x ( 亚麻 ) M a i z e
M a ngo l d （ 甜菜 ） C ot t on M i l l e t R ye
S pi na c h （ 菠菜 ） L upi ns R a pe S oya
S w i s s c ha r d （ 叶 用 甜菜 ） O a t s w he a t S w e de （ 芜箐 甘蓝 ）
T a bl e be e t （ 食用 甜菜 ） pot a t o
R ubb e r
T ur ni ps ( 芜 箐 )
Potassium deficiency symptoms
1,When K+ is slightly deficient,there may be no
obvious symptoms,but plant growth will be reduced
(hidden hungry),
2,At higher levels of K+ deficiency there will be
chlorosis (yellowing黄化 ) or necrosis (dying tissue坏
死 ) on the leaf tips and leaf edge.
Because K is a mobile nutrient,K deficiency will
first appear on lower leaves (maize,cereals,fruit trees),
but in some species such as clover irregularly
distributed necrotic spots occur on the leaves.
Potassium deficiency symptoms
For corn,the margins of the lower
leaves turn brown,This development of
dead tissue is accompanied by a striped
appearance in the remainder of the leaf.
The entire leaf has a very distinct light
green appearance when viewed from a
distance.
The striping associated with K
deficiency in corn can be easily confused
with deficiency symptoms for sulfur (S),
magnesium (Mg),and zinc (Zn).
Potassium deficiency symptoms
The margins of the leaflets turn
light green to yellow when K is
deficient for soybean production,As
with corn,these deficiency symptoms
first appear on the lower leaves,With
maturity,the deficiency symptoms
expand to leaves closer to the top of
the canopy
Potassium Deficiency in Soybeans
Potassium deficiency symptoms
Potassium deficiency in alfalfa
is characterized by yellow or white
spots on the margins of the leaflets,
with symptoms first appearing on
the older plant tissue,This could be
confused with insect damage,
Potassium Deficiency in Alfalfa
K deficiency of Maize
K deficiency of Apple trees
Bluish green,with
slight marginal and
intervenal chlorosis,
followed by marginal
scorching（烧焦，枯
萎）,either brown or
grayish brown color.
? K deficiency of
citrus trees,older
leaves die and fall
off,kraurosis of
younger leaves from
tip and margins
? The deficient plant on the left has yellow scorched
older leaves,which dry and papery,The plant on the
right is healthy,Yellowing and scorching of the older
leaves begins at the edges (left and centre) and
eventually spread between the main veins towards
the centre and leaf(right)
? Fruit fails to expand at the stem end.
Potassium deficiency symptoms
３, K+ deficiency may also be evident in the
form of increased lodging,winter injury,
drought stress,or reduced disease or insect
resistance.
4,Abnormal development of tissues (such as
cambium形成层, cuticle角质层 ） and cell
organelles (such as chloroplast and
mitochondria) is observed in k+ deficient
plants.
Relationships of grain yields and k
concentration in the sap of cereal leaf
Excessive levels of potassium
1,K+ is not directly toxic to plants
or other organisms.
2,High soil K can inhibit uptake of
other cations,such as Ca
deficiency
3,K can counteract problems of excess N
a) N stimulates vegetative growth that
may lead to
lodging or disease or insect
susceptibility.
b) K has the opposite effect
Excessive levels of potassium
Soil Potassium
Total K in the Soil
1,The total K content in the soil
ranges between 0.3-2.5%,The
textbook mentions some clay soils
may have more than 4% K.
2,the greatest part of K is bound in
primary minerals and in the
secondary clay minerals (such as
illites伊利石 and chlorite绿泥石 ).
Forms of K in the soil
1,Solution K (Dissolved K+ ions)
a) 1-10 mg/L
b) Solution K is very low compared to
crop
requirements
c) Plants are very efficient at extracting
K to very
low solution levels
Potassium concentration of some primary and
secondary clay minerals (Scheffer and
Schachtschabel 1982)
Biotite,50-400mmol/m3; musicovite,2.5mmol/m3
M i n e r a l s K c onc e nt r a t i on i n g/ kg
Al k a l i f e l ds pa r s 钾 长石 32 - 120
Ca - N a f e l ds pa r s 钙 - 钠 长石 0 - 24
M us c ovi t e ( K m i c a ) 白 云母 60 - 90
B i ot i t e ( M g m i c a ) 黑云母 36 - 80
I l l i t e 伊利石 32 - 56
V e r m i c ul i t e 蛭石 0 - 16
C hl or i t e 绿泥石 0 - 8
M ont m or i l l oni t e 蒙脱石 0 - 4
Forms of K in the Soil
2,Exchangeable K
a) Weakly sorbed on the surfaces of clay or organic
matter.
b) K may typically occupies 2 to 5% of the cation
exchange sites in a soil.
c) The term,exchangeable” means that the K sorbed
to the clay or organic matter surfaces can be
replaced by other positively charged cations from
the soil solution.
d) This form of K can replace the K taken up from the
soil solution.
3,Non-exchangeable K
a) Also called ―fixed K‖
b) It is held within the clay layers by
strong
bonds
c) It is inaccessible (not accessible) to
plant roots
d) It may take many years for this form
of K to become available to the plant.
Forms of K in the Soil
P-position
E-position
i-position
Gapon efficients (K+/Mg2+),
P-position,2.21 (mol/m3)-1/2 ;e-position(mol/m3)-1/2,102;i-position infinite
Forms of K in the soil
4,Mineral K
a) Contained in rocks such as feldspar
(KAlSi3O8)
and mica
b) The release of K from these rocks is
very,very
slow.
K fractions of a sandy loam and a loamy sand soil
(Martin and Sparks 1983) E x c h a n g e K +
( C a C I 2 )
N o n e x c h a n g e K
+
( H NO 3 )
M i n e r a l K
+
T o t a l K
+
I n mol K k g
- 1
s o i l
S a n d y l o a m 1, 7 2 2, 2 0 3 7, 6 4 1, 5
L o a my s a n d 1, 1 5 2, 0 9 3 1, 3 3 4, 5
The K in the solution and exchange K are called ―easily available K‖
Nonexchange K+ is called as ―slowly releasing potassium
or slowly available K‖
Forms of K in the soil
5,Plant available K includes both
solution K and exchangeable K
6,K is not bound in organic forms like
N and P,It is quickly leached out of
crop residues and roots when the
plant dies.
Potassium transformations in the soil
1,Clay Fixation and Release
１ ) Clay fixation refers to the process by
which K is trapped between layers of
clay.
２ ) It is temporarily unavailable for plant
use,
３ ） Clay fixation and release is affected by soil
factors such as:
a) Soil water – if the soil is very dry the
clay layers squeeze together and the K is
trapped,If the soil is wet,the clay layers
are forced apart and some K is released.
(very slowly)
(b) H+and NH4+ – can compete with K+ for
K+ fixing binding site,as pH increases,
there are fewer H+ ions on the exchange
sites,and more K+ is bound;
(c) CEC – as CEC goes up,more K+ is
bound
Potassium transformations in the soil
d) Fixing power of the 2:1clay minerals
Older vermiculite>illite>smectite (蒙皂石 ）
>kaolinite
e) Soils with high K-fixing capacities show
little response to large amounts of K
fertilizer because the surplus of available
K quickly binds to clays,On the other
hand,these soils are generally able to
meet crop needs,because they already
have a large amount of K in storage.
Potassium transformations in the soil
Potassium transformations in the soil
2,Cation exchange (Sorption and desorption)
a) K+ sorbs to (sticks to) the negative surface
of clay due to weak electrostatic attraction.
b) When solution K+ is depleted (goes down),
the K+ desorbs from the soil and enters the
soil solution.
3,Competition with other cations
4,Weathering
Affected by factors such as
temperature and moisture
Potassium transformations in the soil
Potassium availability
1,Readily available
a) Labile K
b) Soil solution and exchangeable K
c) < 2% of total K in soil
2,Slowly available or less readily
available
a) Non-exchangeable,fixed K
b) 1-10% of total K in soil
3,Unavailable or mineral
a) K contained in primary soil minerals
b) 90-98% of the K in the soil
Potassium availability
Soil Solution
K+
Primary
Minerals
KRelease
SorptionDesorptionWeathering
Potassium availability
1,Leaching – leaching is affected by the
concentration of K+ in the soil
solution and the amount of water
moving through the soil,Because K+
in the soil solution is very low,
leaching losses of K are generally low,
The loss of K to leaching is only a
problem where rainfall is very high or
under irrigated conditions,
Potassium loss from soil
2,Erosion removes the surface soil
where plant available K+ is highest.
Reducing erosion can maximize
the amount of K+available for
crops.
Potassium loss from soil
Potassium fertilizer
Potassium chloride (muriate of potash)
1,KCl
2,0-0-60
3,90% of all K fertilizer used in the
U.S,is KCl,It is economical.
4,Varies in color from pink to white
depending on the mining and
recovery process
5,Can be directly applied or blended
with other fertilizers.
6,Cl may increase yields of some
crops and also increase disease
resistance in some small grains
7,Some lower grade fertilizer
types(33-%-41%K),which contain
substantial amount of NaCI and are
therefore suited to natrophilic crops
(sugar beet,cabbage,oats)
Potassium chloride (muriate of potash)
Potassium sulfate (sulfate of potash)
1,K2SO4
2,0-0-50
3,About 5% of the K fertilizer used
in the US is K2SO4
Potassium sulfate (sulfate of potash)
4,Primarily used for crops such as
tobacco,potatoes,and a few
vegetable crops that are
negatively affected by Cl from
KCl fertilizer.
5,May also be used when S is
required,
Potassium nitrate (nitrate of potash)
1,KNO3 – provides both N and K
2,13-0-45
3,Too expensive for common use,In
the U.S.,it is primarily use for
horticultural and greenhouse crops
such as celery,tomatoes,potatoes,
leafy vegetables,and a few fruit
crops.
Potassium magnesium sulfate
1,K2SO4 + 2 MgSO4
2,0-0-22-22S
3,Primarily produced from mines in
Germany and France,It is used as
a source of Mg and S.
4,Applied directly or blended with
other fertilizers
Plant ash and flue ash
Plant ash K2CO3(K2SO4 and KCI)
0-0-0.67~35.4
Avoid from leaching in the storage.
Applied in all crops and soil apart from
saline soil
Flue Ash K2SiO4
k2O,8%~40%
only used as basal,topdress or
siderdress,but not for pop-up.
C o t t o n s e e d h u l l a s h 0 — 2 7, 0 — — — —
C o t t o n s e e d m e a l 6 t o 7 2, 5 1, 5 0, 4 0, 9 0, 2 —
S w e e t p o t a t o s k i n s b o i l e d
( a s h ) — 3, 2 9 1 3, 9 — — — —
S w e e t p o t a t o e s 0, 2 0, 1 0, 5 — — — —
T a n k a g e 7, 0 1, 5 3 t o 1 0 — — — —
T e x t i l e s l u d g e s 2, 8 2, 1 0, 2 0, 5 0, 2 — —
W o o d a s h e s 0, 0 2, 0 6, 0 20,0 1, 0 — —
Fl y a s h,
c o a l
w o o d
0, 3
0, 1
—
0, 6
0, 1
1 0, 0
0, 4 8
9, 8
—
0, 6 6
—
—
—
—
G r a p e s k in s ( a s h ) — 3, 6 3 1, 0 — — — —
? A,Some crops are sensitive to high
amounts of chloride,This chlorophobic
species(忌氯作物） include tobacco,
grapes,fruit trees,sugar cane,potatoes,
strawberries,cucumber and onions,It
is preferential to treat these crops with
potassium sulphate.
?
Management of K fertilizer
Effect of a varying chloride/sulphate on grope yield
(Edelbauer 1978)
N u t r i e n t s o l u t i o n
K C I,me / L K 2 SO 4,me / L
G r a p e y i e l d
g / p o t
W e i g h t o f c l u s t e r
g
N o, o f
c l u s t e r / p o t
4, 0 0 111 5 8, 9 1, 8 9
2, 5 1, 5 149 7 0, 5 2, 1 0
1,0 3, 0 252 8 4, 2 3, 0 0
0 4, 0 254 9 1, 3 2, 7 8
? Most field crops are not sensitive
to chloride and are generally
treated with muriate,Oil palms
and coconut even appear to have a
chloride requirement.
? Potassium nitrate is mainly used
for spraying on leaves of fruit trees
and horticultural crops
Management of K fertilizer
B,K uptake in plants is affected by
soil water,aeration,temperature,
and tillage.
C,Use small,frequent applications
on soils with high K fixation
capacity and high leaching.
Management of K fertilizer
1,Surface application
a) K has limited mobility in the soil
b) Surface-applied K will move to roots
very slowly
2,Broadcast and incorporate
a) Places K in root zone
b) Maximizes K fixation on fine-textured
soils with high fixation potential
Fertilizer placement
3,Band placement
a) Minimizes contact between soil and
fertilizer
b) Can reduce K fixation
c) Most beneficial on low K soils with
high fixation capacity
Fertilizer placement
Deficient soils
? Potassium deficiency occurs
commonly on a number of different
soil types.
? Light sandy acid soil
? Organic soil
? Heavily cropped soil
