What it does

Potassium deficiency affects canopy photosynthesis, thus affecting crop growth.

Why and where it occurs

K deficiency in rice is more common under the following crop management practices:

excessive use of N or N and P fertilizers with insufficient K application
direct seeded 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.

Soils, which are particularly prone to K deficiency include:

Soils inherently low in K

coarse-textured soils with low CEC and small K reserves (e.g., sandy soils in northeast Thailand, Cambodia)
highly weathered acid soils with low CEC and low K reserves, e.g., acid upland soils (Ultisols or Oxisols) and degraded lowland soils (e.g., North Vietnam, northeast Thailand, Cambodia, Lao PDR).

Soils on which K uptake is inhibited

lowland clay soils with high K fixation
soils with a large K content but very wide (Ca + Mg)/K ratio
leached, "old" acid sulfate soils with a small base cation content
K deficiency may occur on acid sulfate soils even when the soil K content is large (Thailand, South Vietnam).
poorly drained and strongly reducing soils
organic soils (Histosols) with small K reserves (e.g., Kalimantan, Indonesia)

The following are symptoms of K deficiency:

Dark green plants with yellowish brown leaf margins or dark brown necrotic spots appearing first on the tip of older leaves
Leaf tips yellowish brown under severe K deficiency
Symptoms appear first on older leaves, then along the leaf edge, and finally on the leaf base
Affected plants with upper leaves short, droopy, and "dirty" dark green
Older leaves change from yellow to brown
Discoloration gradually appears on younger leaves if deficiency is not corrected
Leaf tips and margins may dry up
Yellow stripes may appear along leaf interveins and lower leaves may bend downward

General pattern of damage is patchy within a field, affecting single hills rather than the whole field

Rusty brown spots on tips of older leaves and later spread over the whole leaf causing it to turn brown and dry if K deficiency is severe
Irregular necrotic spots may also occur on panicles.
Stunted plants with smaller leaves, short and thin stems
Tillering is only reduced under very severe deficiency
Greater incidence of lodging.
Early leaf senescence, leaf wilting, and leaf rolling when temperature is high and humidity is low.
Large percentage of sterile or unfilled spikelets
Unhealthy root system (many black roots, reduced root length and density), causing a reduction in the uptake of other nutrients.
Poor root oxidation power, causing decreased resistance to toxic substances produced under anaerobic soil conditions
Increased incidence of diseases, where inappropriate amounts of fertilizers are used

Click on images to enlarge

Potassium deficiency also affects yield

Estimate K input from indigenous sources to assess site-specific K requirements.
Increase K uptake by improving soil management practices on root health (e.g., deep tillage to improve percolation to at least 3-5 mm d-1 and to avoid excessively reducing conditions in soil).
Establish an adequate population of healthy rice plants by using high-quality seed of a modern variety with multiple pest resistance, and optimum crop maintenance (water and pest management).
Incorporate rice straw. If straw burning is the only option for crop residue management, spread the straw evenly over the field (e.g., as it is left after combine harvest) before burning. Ash from burnt straw heaps should also be spread over the field.
Apply optimum doses of N and P fertilizers and correct micronutrient deficiencies. Apply K fertilizers, farmyard manure, or other materials (rice husk, ash, night soil, compost) to replenish K removed in harvested crop products.

View full fact sheet:
Potassium deficiency on IRRI Rice Knowledge Bank