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RLO 4 Lesson: Role and deficiency symptoms of potassium (K) in rice. After completing this lesson, you will be able to: Know the role and deficiency symptoms of potassium (K) in rice crop. Understand the causes and occurrence of K deficiency in rice. Role of potassium in rice.
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RLO 4 Lesson: Role and deficiency symptoms of potassium (K) in rice After completing this lesson, you will be able to: Know the role and deficiency symptoms of potassium (K) in rice crop. 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.
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. It is important to note that:
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. Contd…. 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. • Contd…. 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 K deficiency symptoms
K deficiency in rice 18794E8480852573EC000E Source: http://www.ipni.net/ipniweb/portal.nsf/0/9AD9BD18794E8480852573EC000EC596 Source: http://www.plantmanagementnetwork.org/pub/cm/research/2004/meter/
Potassium excess Excess potassium may cause deficiencies in magnesium and possibly calcium.
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. • Contd……
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 content. • 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 manures.
