1. Potassium (K)

2. Potassium is an essential plant nutrient and is required in large amounts for proper growth and reproduction of plants.
Potassium is considered second only to nitrogen, when it comes to nutrients needed by plants, and is commonly considered as the “quality nutrient.”

3. It affects the plant shape, size, color, taste and other measurements attributed to healthy produce. 

4. Generally low in sandy soils. Availability of K minerals:
K in most soil is large.
Generally low in sandy soils.
Availability of K minerals:
Biotite> muscovar> K-feldspars

5. Available amount from different forms:
Mineral K: ppm
Non-exchangeable: ppm
Exchangeable: ppm
Solution K: ppm

6. Equilibria and cycling of K in soils
Fixed K is mainly in clay minerals like illite, vermiculite and chlorite.
Feldspars and micas are very resistant to weathering.
Unavailable K % of total

7. Unavailable K- 90-98% of total soil K Slowly available K-1-10% Readily available K-0.1-2%

8. Exchangeable vs. Non-exchangeable K
Readily buffers
soil solution K
Non-Exchangeable K
Slowly buffers
soil solution K
Soil tests measure exchangeable K

9. Functions

10. -Enzyme activator -Regulates osmotic pressure in roots
-Enzyme activator -Regulates osmotic pressure in roots. -Maintains turgor pressure of guard cells and regulates opening of stomata, thus, controlling photosynthesis and transpiration.

11. -Needed in ATP synthesis which is used in translocation of sugars from leaves, N uptake and protein synthesis. -Strengthens straw of grain crops and prolongs the life of the flag leaf. -Increases pest and diseases resistance.

12. Alleviation of Effects
POTASSIUM IN CROP PRODUCTION
Alleviation of Effects
of Stress Factors
Water
Regime
Photosynthesis K
Protein
Synthesis
Enzyme
Activation
Cell elongation
Phloem Export
of Photosynthates

13. Environmental Factors Affecting K Availability to a Plant

14. Soil moisture Soil Aeration
Low soil moisture results in more tortuous path for K diffusion – takes longer to get to root
Increasing K levels or soil moisture will increase K diffusion
Increase soil moisture from 10 to 28 % can increase toatl K transport by up to 175 %
Soil Aeration
High moisture results in restricted root growth, low O2 and slowed K absorption by the root

15. Soil temperature Soil pH
Low temperature restricts plant growth and rate of K uptake
Providing high K levels will increase K uptake at low temperatures
Reason for positive response to banded starter
Soil pH
At low pH, K has more competition for CEC sites
As soils are limed, greater amount of K can be held on CEC and K leaching reduced.

16. Leaching
K leaching can occur on course textured or muck soils particularly if irrigated
Large fall K applications to sandy or muck soils discouraged

17. Uptake, Translocation & Assimilation of Nutrients
Taken up high rate by plant tissue.
K is taken up by active mechanism. Of all the essential nutrient cations K is the only one which can be transported against an electrochemical gradient into plant cell.

18. K in plant is very mobile
K in plant is very mobile. The main transport direction is towards the merismatic tissues. Thus when plant is sufficiently supplied with N and vigorously growing, K uptake is high. The bulk of K mainly taken up during the vegetative stage.

19. K uptake and retention in plants are competitively affected by H+, Ca ++, Mg++, and N+. K accumulation in xylem and mesophyll cells lowers the osmotic potential of cell sap and increases uptake and retention of water. Thus, plants well supplied with K require relatively lower amounts of water.

20. Such plants also have lower transpiration rate
Such plants also have lower transpiration rate. K in guard cells appear to regulate stomata opening and closing, hence regulating transpiration.

21. K enhances translocation of assimilates through stimulation of ATP production which is needed in the loading of photosynthesis in the sieve tubes (phloem).

22. Stomata regulating transpiration and CO2 uptake
The transport of K+ across the plasma membrane and tonoplast causes the turgor changes of guard cells. Stomata open when guard cells accumulate potassium (red dots), which lowers the cells’ water potential and causes them to take up water by osmosis. The cells become turgid.

23. Deficiency Symptoms

24. Chlorosis – scorching of plant leaves, with yellowing of the margins of the leaf. This is one of the first symptoms of Potassium deficiency. Symptoms appear on middle and lower leaves.
Slow or Stunted growth – as potassium is an important growth catalyst in plants, potassium deficient plants will have slower or stunted growth.   

25. Poor resistance to temperature changes and to drought – Poor potassium uptake will result in less water circulation in the plant. This will make the plant more susceptible to drought and temperature changes.

26. Defoliation- left unattended, potassium deficiency in plants results in plants losing their leaves sooner than they should. This process might become even faster if the plant is exposed to drought or high temperatures. Leaves turn yellow, then brown and eventually fall off one by one.

27. Other symptoms of Potassium deficiency:
Poor resistance to pests
Weak and unhealthy roots
Uneven ripening of fruits

28. Potassium deficiency
in banana
Potassium deficiency
in citrus
Potassium deficiency  in potato

29. Relative distribution of total carbohydrates
between shoot and roots (%)
Control
K Deficiency 16 3

31. Potassium is highly needed for wood production.
Potassium is driving force for expansion of wood producing cells

32. Plants suffering from environmental stress factors such as drought, high light intensity and salinity have larger requirement for potassium

33. Growth of bean plants with low K supply under low and high light intensity
Low light
High light

34. SHADED
PART
Plants grown under high light intensity require more K than plants grown under low light

35. Enhancement of leaf symptoms of K-deficieny by high light
Partially shaded K-deficient bean leaves

36. Potassium deficiency makes plants sensitive to environmental stress factors.
Plants under environmental stress factors need additional potassium

37. Conclusions
Potassium has several critical roles in plant growth and yield formation including cell elongation, maintenance of turgor pressure and photosynthesis, stomatal closure, protein synthesis and photoassimilate transport.
Potassium transporter proteins play critical role in K uptake and translocation (contributing to cell elongation) and tolerance to Na toxicity.

38. Plants exposed to high light intensity or grown under long-term sunlight conditions like in southern countries in Northern Hemisphere have much larger K requirement.
Improving K nutritional status of plants is a major contributing factor to the protection of plants from environmental stress factors under marginal conditions