Origin of soil K is primary minerals from which soil is formed.
clay- illite, vermiculite and chlorite
Plants take up K in the ionic form (K+)
Availability of K in the soil
Relatively unavailable K (90-98%)
- part of the crystal structure of minerals
Slowly available (1-10%) K that is bonded in the interlayer
position of clays.
readily available - 1-2% - K on cation exchange sites
and K in soil solution.
weathering usually moves K towards the available forms.
However, applying large amounts of fertilizer K can reverse
K fixation -- Trapped in the interlayer of illite and vermiculite
Factors affecting availability of K
Soil parent material
- feldspars and micas are high in K. If these minerals are
present the soil will be high in K.
Soil texture - Fine textured soils have more K than coarse
- Norfolk Sandy Loam - 1,600 lbs. total K2O / acre
- Cecil Sandy Clay Loam -11,800 lbs. total K2O / acre
Intensity of weathering - High temperature and rainfall cause
faster breakdown of minerals but also more leaching
- Although soils contain large total amounts of K it is usually
necessary to add K with fertilizers.
Effect of pH on retention of applied K
- Leaching loss of K from a sandy soil was greatly reduced when
the soil was limed.
Added K Lost by Leaching
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.
Soil factors to consider in K fertilization
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
Fixation of K is generally not a problem in NC
Leaching - Occurs on sandy coastal plain soils
detect buildup in topsoil over the years with soil testing
accumulate in the B horizon if present
applications are necessary because of leaching and high
Placement - Broadcast application is generally as effective
B. K fertilizer Mining, manufacture, and properties
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)
K Fertilizer Materials
muriate of potash 60%
- 90% of U.S. consumption
- completely water soluble
- contains Cl
K2SO4 - Potassium sulfate
- 50% K2O 18% Sulfur
- provides SO4 as well as K and must contain less than 2.5%
- used only on Cl sensitive crops because it is more
expensive than KCl
K2SO4 * MgSO4 - sulfate of potash-magnesia, Sul-PO-Mag,
- 22% K2O, 11% Magnesium, 22% Sulfur
- max Chloride 2.5 %
by reacting with KCl with sodium nitrate
- 44% K2O 13% N
- no Cl
K fertilization of Crops
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
Choice of K fertilizer materials
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.
the accompanying elements Mg or SO4 may be needed Cl may
crop sensitivity to chlorine
- Tobacco is sensitive to chlorine; an excess affects burning
- Irish potatoes are sensitive to chlorine.
K2SO4 produces better keeping and chipping qualities.
High K levels can inhibit Ca uptake by the peg. K may be
applied to the crop preceding or several months before to
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.
Luxury consumption of K, Plants will take up more K than they
K in Clover
Crop removal of K
g. Deficiency symptoms
h. Fertilizer list