1.
Origin of soil K is primary minerals from which soil is formed.
a.
K-feldspars
b.
mica
c.
clay- illite, vermiculite and chlorite
2.
Plants take up K in the ionic form (K+)
3.
Availability of K in the soil
a.
Relatively unavailable K (90-98%)
- part of the crystal structure of minerals
b.
Slowly available (1-10%) K that is bonded in the interlayer
position of clays.
c.
readily available - 1-2% - K on cation exchange sites
and K in soil solution.
d.
weathering usually moves K towards the available forms.
However, applying large amounts of fertilizer K can reverse
this.
4.
K fixation -- Trapped in the interlayer of illite and vermiculite
(2:1 clays)
5.
Factors affecting availability of K
a.
Soil parent material
- feldspars and micas are high in K. If these minerals are
present the soil will be high in K.
b.
Soil texture - Fine textured soils have more K than coarse
textured soils.
- Norfolk Sandy Loam - 1,600 lbs. total K2O / acre
- Cecil Sandy Clay Loam -11,800 lbs. total K2O / acre
c.
Intensity of weathering - High temperature and rainfall cause
faster breakdown of minerals but also more leaching
loss.
- Although soils contain large total amounts of K it is usually
necessary to add K with fertilizers.
6.
Effect of pH on retention of applied K
- Leaching loss of K from a sandy soil was greatly reduced when
the soil was limed.
| Soil
pH |
Percent
Added K Lost by Leaching |
| 5.1 |
61 |
| 6.3 |
24 |
-
at pH 5.1 a large portion of the exchange complex is occupied
by Al3+ which is held more tightly than K. Therefore,
K is blocked from the exchange site.
- When limed Ca2+ occupies the exchange sites and K can displace
the Ca2+ and be held in the soil.
7.
Soil factors to consider in K fertilization
a.
Ability of the soil to retain and supply K ]
- Sandy Soils have low CEC and low K reserves
- Fine textured soils have higher CEC and K reserves
b.
Fixation of K is generally not a problem in NC
c.
Leaching - Occurs on sandy coastal plain soils
- Cannot
detect buildup in topsoil over the years with soil testing
- Will
accumulate in the B horizon if present
- Annual
applications are necessary because of leaching and high
crop requirements
d.
Placement - Broadcast application is generally as effective
as banding
B.
K
fertilizer Mining, manufacture, and properties
a.
Found as water-soluble salts in large deposits.
New Mexico and Canada.
Composed mainly of KCl
(sylvite), KCl + NaCl (Sylvinite),or
K2SO4 + MgSO4 (Langbeinite).
These salts are mined and refined to produce K fertilizers.
Only 15% of potash used in the U.S. is produced domestically.
Most of the rest is imported from Canada.
Potassium Fertilizer Production and Technology (IPI)
Shaft,
underground mining
Solution
Mining
b.
K Fertilizer Materials
1.
KCl -
muriate of potash 60%
- 90% of U.S. consumption
- completely water soluble
- contains Cl
c.
K2SO4 - Potassium sulfate
- 50% K2O 18% Sulfur
- provides SO4 as well as K and must contain less than 2.5%
Cl
- used only on Cl sensitive crops because it is more
expensive than KCl
d.
K2SO4 * MgSO4 - sulfate of potash-magnesia, Sul-PO-Mag,
K-Mag
- 22% K2O, 11% Magnesium, 22% Sulfur
- max Chloride 2.5 %
e.
KNO3 potassium
nitrate
manufactured
by reacting with KCl with sodium nitrate
- 44% K2O 13% N
- no Cl
C.
K fertilization of Crops
a.
Benefits to plants
- improves stalk strength and size (reduces lodging )
- improves drought resistance
- winter hardiness improved - reduces winter kill of perennial
grasses like coastal bermuda.
- increases resistance to some diseases and nematodes
- crop quality is improved - tobacco, peach storage qualities,
corn grain, soybeans
b.
Choice of K fertilizer materials
- I
f no special conditions are a factor, one K source
is as good as another. Choice based on price per pound
KCl is cheapest and used in most fertilizers.
- Consider
the accompanying elements Mg or SO4 may be needed Cl may
be detrimental.
- Consider
crop sensitivity to chlorine
- Tobacco is sensitive to chlorine; an excess affects burning
quality
- Irish potatoes are sensitive to chlorine.
K2SO4 produces better keeping and chipping qualities.
c.
Peanuts
High K levels can inhibit Ca uptake by the peg. K may be
applied to the crop preceding or several months before to
avoid this.
d.
Soils low in Magnesium - High K rates can supress Mg uptake
causing Mg deficiency. Important in pastures; Mg deficiency
in forage can cause grass tetany a disease of grazing animals.
e.
Luxury consumption of K, Plants will take up more K than they
need.
| lbs.
K2O |
%
K in Clover |
Yield
Per/A |
| 0 |
0.5 |
2350 |
| 120 |
2.5 |
3200 |
| 300 |
3.8 |
3880 |
| 600 |
6.8 |
3850 |
f.
Crop removal of K
g. Deficiency symptoms
h. Fertilizer list