1. Role and deficiency symptoms of potassium (K) in rice

2. Role and deficiency symptoms of potassium in rice
Role of Potassium
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 . 

3. It is important to note that:
Role and deficiency symptoms of potassium in rice
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.

4. Role and deficiency symptoms of potassium in rice
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 leaves.
Yellow stripes may appear along leaf interveins, and lower leaves may bend downward.

5. Role and deficiency symptoms of potassium in rice
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.
Increased incidence of lodging.
Tillering reduced under very severe deficiency.
Early leaf senescence, leaf wilting, and leaf rolling, especially when temperature is high and humidity is low.

6. Role and deficiency symptoms of potassium in rice
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 nutrients.
Increased incidence of diseases, particularly brown leaf spot, bacterial leaf blight, sheath blight, sheath rot, stem rot, and blast

7. Role and deficiency symptoms of potassium in rice
K deficiency in rice
Source:
Source:

8. Role and deficiency symptoms of potassium in rice
Toxicity Symptoms of Potassium
Excess potassium may cause deficiencies in magnesium and possibly calcium.

9. Role and deficiency symptoms of potassium in rice
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 conditions.
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.

10. Role and deficiency symptoms of potassium in rice
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.

11. Role and deficiency symptoms of potassium in 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.

12. Role and deficiency symptoms of potassium in rice
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 content.
Organic soils with small K reserves.

13. Role and deficiency symptoms of potassium in rice
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 manures.

14. Sources of potassic (K) fertilizers
Role and deficiency symptoms of potassium in rice
Sources of potassic (K) fertilizers
Name
Formula
Content
Comments
Potassium chloride
(Muriate of potash)
KCl
50% K
Muriate of potash (60% K2O)
Potassium nitrate
KNO3
37% K, 13% N
In compounds (44% K2O)
Potassium sulfate
K2SO4
40–43% K, 18% S
In compounds (50% K2O)
Langbeinite
K2SO4, MgSO4
18% K,
11% Mg, 22% S
Quick-acting
Compound fertilizers
N + P + K
Variable
Common in rice

15. Role and deficiency symptoms of potassium in rice
Appropriate K management results in better yield of rice