#Soil_Scientists

2. BEHAVOIR OF POTASSIUM FERTILIZER IN
SOIL AND FACTERS EFFECTING ON ITS
AVAILABILITY

3. History of Potassium
Potassium symbol K comes from “Kalium” the
name of the element in Germany and
Scandinavia.
Potassium metal was first isolated in 1807 by Sir
Humphry Davy who derived it from caustic potash
by the use of electrolysis of the molten salt with the
newly discovered voltaic pile.
Potassium was the first metal that was isolated by
electrolysis.

4. Introduction
▪ Potassium is an essential plant nutrient
and is required in large amounts for
proper growth and reproduction of
plants.
▪ It affects the plant shape, size, color,
taste and other measurements
attributed to healthy produce.
▪ Plants absorb potassium in its ionic
form, K+.

5. Percentage of potassium in soil
Portion of total K Form of K
90 to 98 percent Potassium containing minerals (Micas,
Feldspars, etc.)
1 to 10 percent Clay minerals (Illitic types)
0.1 to 2 percent Exchangeable K+
and Soil solution K+

6. In
Roles of Potassium in Plants
Photosynthesis, potassium regulates
the opening and closing of stomata,
and therefore regulates CO2 uptake.
Potassium triggers activation of
enzymes and is essential for production
of ATP.
Potassium plays a major role in the
regulation of water in plants (osmo-
regulation).

7. (Cont.)
Known to improve drought resistance.
Potassium is essential at almost every step of the protein
synthesis.
In starch synthesis, the enzyme responsible for the process
is activated by potassium.

8. Deficiency Symptoms of Potassium
▪ Chlorosis
▪ Slow or Stunted growth
▪ Poor resistance to temperature changes
▪ Poor resistance to drought
▪ Defoliation
▪ Other symptoms
▪ Poor resistance to pests
▪ Weak and unhealthy roots
▪ Uneven ripening of fruits

9. K Deficiency Symptoms in Field Crops

10. Potassium in soils
The total K content of soils frequently exceeds 20,000 ppm (parts per million).

11. 1) Unavailable Potassium
90-98% of total soil K is found in this form.
Feldspars and micas are minerals that contain most of the K.
Plants cannot use the K in this crystalline-insoluble form.
Over long periods of time, these minerals weather (break down) and K is
released.
As these minerals weather, some K moves to the slowly available pool.
Some also moves to the readily available pool.

12. 2) Slowly Available Potassium
This form of K is thought to be trapped between layers of clay minerals and
is frequently referred to as being fixed.
Growing plants cannot use much of the slowly available K during a single
growing season.
This slowly available K is not measured by the routine soil testing
procedures.
Slowly available K can also serve as a reservoir for readily available K.
While some slowly available K can be released for plant use during a growing
season, some of the readily available K can also be fixed between clay layers
and thus converted into slowly available K

13. 3) Readily Available Potassium
Potassium that is dissolved in soil water (water soluble) plus that held on the
exchange sites on clay particles (exchangeable K) is considered readily available
for plant growth.
The exchange sites are found on the surface of clay particles.
This is the form of K measured by the routine soil testing procedure.
Plants readily absorb the K dissolved in the soil water.
As soon as the K concentration in soil water drops, more is released into this
solution from the K attached to the clay minerals.
The K attached to the exchange sites on the clay minerals is more readily
available for plant growth than the K trapped between the layers of the clay
minerals.

14. Potassium Releasing From Mica
Its behavior in soil is influenced mostly by cation exchange
reactions than by microbial activity.

16. Factors affecting Potassium Uptake
1) Soil Moisture
2) Soil Aeration and Oxygen Level
3) Soil Temperature
4) Soil pH
5) Leaching
Common fertilizer sources of K.

17. Inorganic sources of K
Material Chemical Formula Content %
potassium chloride KCl 60 %
potassium-magnesium sulfate K 2SO 4-2MgSO 4 20 %
potassium nitrate KNO 3 44 %
potassium sulfate K 2SO 4 50 %
K2 O

18. Organic sources of K
Break down of crop residues Manures
A. Majority of K is soluble
a. 80% of total K in manure available the year of application
b. 10% of total K is available 2nd
year after application
c. 5% of total K is available 3rd
year after application
B. Book values
a. Dairy solids- 9 lb K2O/ton
b. Dairy liquids-20 lb K20/1000gal
C. Book solids

19. Potassium losses from Soil
Erosion: Erosion is one of the main pathways through
which K is lost from the soil.
Runoff: Runoff is one of the main pathways through
which K is lost from the soil.
Leaching: Annual leaching loss of K from the soils
in a humid region under agricultural production
(receiving only a moderate rate of K fertilizer) is usually
about 25 to 50 kg K/ha.

20. Harvesting: Plants take up very large amounts of
K.
Management Practices for Potassium
Suggested management practices for K vary with crop.
The best strategy would be to apply potash fertilizers before seeding followed
by annual top-dress applications.
The annual applications should be based on the results of routine soil tests for
K.
Any potash needed for small grain production can be applied in a band near
the seed at planting or broadcast and incorporated before planting.

21. When applied in a band, the recommended broadcast rate of potash can be
reduced by one-half without causing a reduction in yield.
Application Method and Timing
Band application concentrate nutrients at or near the root zone
Banded K should be placed beside and below the seed level to reduce
potential damage or by using very low rates
Band K application are recommended in soil with strong capacity
to retain K
Deep banding K can be more effective for ridge-till or no till, where
K tends to accumulate at or near the soil surface

22. Timing of K application typically has little or no impact on K use
efficiency by crops; except in the rare soil with very high K fixing
Influence of Potassium on Crop Quality
The economic return from the investment in K can originate from:
(1)Improvement in total yield;
(2)A greater percentage of total yield which is marketable;
(3)Better crop quality;
(4)Lower cost per unit of production;
(5)Disease resistance;


23. Thank you !
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