Role and deficiency symptoms of Potassium in Rice

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Transcript Role and deficiency symptoms of Potassium in Rice

Lesson: Role and deficiency symptoms of potassium (K) in rice
After completing this lesson, you will be able to:
1. Know the role and deficiency symptoms of potassium (K) in rice
2. Understand the causes and occurrence of K deficiency in rice
Role of potassium in rice
 Essentially involved in osmoregulation and enzyme activation.
 Regulates transpiration by stomata and transport of assimilates.
 Provides strength to plant cell walls .
 Increases leaf area and chlorophyll content.
 Delays leaf senescence, and hence contributes to greater canopy
photosynthesis and crop growth.
 Increases the number of spikelets per panicle, percentage of filled
grains, and 1,000-grain weight.
 Improves the plant’s tolerance of adverse climatic conditions,
lodging, insect pests, and diseases.
It is important to note that:
 Deficiency symptoms tend to occur in older leaves first,
because K is very mobile within the plant and is remobilized
to young leaves from old leaves.
 Yield response to K fertilizer is only observed when the
supply of other nutrients, especially N and P, is sufficient.
 K deficiency is often not detected because its symptoms are
not as easy to recognize as those of P and N deficiency, and
symptoms tend to appear during later growth stages.
K deficiency symptoms
 Leaf tips are yellowish brown, and later margins may dry up.
 Symptoms appear first on older leaves, then along the leaf edge,
and finally on the leaf base.
 Upper leaves are short, droopy, and dark green in affected plants.
 Older leaves change from yellow to brown and, if the deficiency
is not corrected, discolouration gradually appears on younger
 Yellow stripes may appear along leaf interveins, and lower leaves
may bend downward.
K deficiency symptoms
 When K deficiency is severe, rusty brown spots appear on the tips
of older leaves and later spread over the whole leaf, causing it to
turn brown and eventually dry up.
 Irregular necrotic spots may also occur on panicles.
 Stunted plants , smaller leaves, short and thin stems.
 Tillering reduced under very severe deficiency.
 Increased incidence of lodging.
 Early leaf senescence, leaf wilting, and leaf rolling, especially
when temperature is high and humidity is low.
K deficiency symptoms
 Increased percentage of sterile or unfilled spikelets caused by
poor pollen viability and retarded carbohydrate translocation.
 Reduced 1,000-grain weight.
 Unhealthy root system (many black roots, reduced root length
and weight), causing a reduction in the uptake of other
 Increased incidence of diseases, particularly brown leaf spot,
bacterial leaf blight, sheath blight, sheath rot, stem rot, and
K deficiency in rice
Potassium excess
Excess potassium may
cause deficiencies in
magnesium and possibly
Causes of K deficiency
 Lower K-supplying capacity of soil.
 Inadequate use of mineral K fertilizers.
 Low recovery efficiency of applied K fertilizers because of
high K-fixation capacity of soil or leaching losses.
 Complete removal of previous crop straw/ residues.
 Wide Na:K, Mg:K, or Ca:K ratios in soil, and sodic/saline
 Presence of excessive amounts of reduced substances in
poorly drained soils (e.g., H2S, organic acids, Fe2+), causing
retarded root growth and hence K uptake.
Causes of K deficiency
 Imbalanced fertilization, especially excessive use of N or
N and P fertilizers with insufficient K application.
 In direct-sown rice during early growth stages, when the
plant population is large and root system is shallow.
 Cultivar differences in susceptibility to K deficiency and
response to K fertilizer. Hybrids need more K than inbred
varieties of rice.
Occurrence of K deficiency
Soils particularly prone to K deficiency include the following types:
 Soils inherently low in K.
 Coarse-textured soils with low CEC and small K reserves
(e.g., sandy soils ).
 Highly weathered acid soils with low CEC and low K
reserves, e.g., acid upland soils and degraded lowlands.
 Lowland clay soils with high K fixation because of the
presence of large amounts of 2:1 layer clay minerals.
Occurrence of K deficiency
 Soils rich in K content but very wide (Ca + Mg)/K ratio
(e.g., some calcareous soils).
 Wide (Ca + Mg)/K ratios result in stronger K
adsorption to cation exchange sites and reduce the
concentration of K in the soil solution.
 Leached, acid sulphate soils with a small base cation
 Organic soils with small K reserves.
Corrective measures (K)
 Follow strictly the fertilization schedule recommended for
rice, particularly suitable for the region.
 Apply optimum doses of N and P fertilizers and correct
micronutrient deficiencies.
 Increase K uptake by improving soil management practices
on root health (e.g., deep tillage to improve percolation and
to avoid excessively reducing conditions in soil).
 Addition of straw of previous crops/ residues and organic
Sources of potassic (K) fertilizers
Potassium chloride
50% K
Muriate of potash (60% K2O)
Potassium nitrate
37% K, 13% N In compounds (44% K2O)
Potassium sulfate
40–43% K,
(Muriate of potash)
In compounds (50% K2O)
18% S
18% K,
11% Mg, 22%
Compound fertilizers N + P + K
Common in rice
Appropriate K management results in better yield of rice