Transcript No Slide Title

Micronutrients
(Fe, Mn, Zn, Cu, B, Cl, and Mo)
December 2005
Jeff Skousen
Professor of Soil Science
Land Reclamation Specialist
WVU
Why Important NOW?!
- Crop Yields- more micros
removed from soil, and some
soils cannot release fast enough
- Fertilizer Purity- impurities
containing micros are removed.
Fe in Soils
•
•
•
•
Fe in soils 0.7 to 55%
Most iron in primary minerals and clays
Low solubility of Fe compounds in soils
Adsorbed iron and total Fe has little
influence on soil solution or plant available
iron
• Solubility of Fe minerals is very low (10-6
to 10-24 M)
Fe in Soil Solution
•
•
•
•
•
Fe2+ and Fe3+
Fe3+ dominant in well drained soils
Solubility pH dependent
Fe (OH)3 + 3H+
=
Fe3+ + 3H2O
For every unit decrease in pH, Fe3+
concentration increases 1,000 fold
Iron Chelates
• Iron complexation by natural or synthetic
compounds may increase dissolved Fe
concentrations and plant availability
• Chelates are soluble organic compounds
that transport Fe from soil minerals to plant
roots
• Natural organic acids such as citric acid and
oxalic acids have chelating properties
Fe in Plants
• Absorbed as Fe2+ or Fe3+
• Important in oxidation reduction reactions in plant
cells
• Used in chlorophyll synthesis
• Immobile in soils and plants
• Deficiency symptoms in younger leaves
• Sufficiency range is 50 to 250 ppm
• Fe toxicity @300 ppm or more (low pH)
Iron deficiency
Factors Affecting Fe Availability
• Soil pH (deficiency in calcareous soils)
• Poor soil aeration and formation of
carbonates in wet cool soils
• Organic matter: Low chelates
• Interactions with Cu and Mn
• Excess Cu, Fe, Mn, P, and Zn reduce Fe
uptake
Iron deficiencies are more likely
to occur in:
a) high pH
b) high organic matter soils
c) calcareous soils
d) a and b
e) a and c
Zinc
• Soil solution concentration governed by pH
• Transported to roots as chelate
• Absorbed as Zn2+ by plants
• Immobile in soils and plants
Zn Deficiency Symptoms
• White or yellow veins on leaves
• Short internodes, rosette appearance of the
leaves
• Early loss of foliage
• Malformation of fruit
• Zn deficiency in sandy soils, calcareous
soils, soils high in P, eroded soils
Zinc deficiency
Factors Affecting Zn Availability
•
•
•
•
pH
Zn incorporation on iron oxide surfaces
Zn incorporation into the dolomite crystals
Immobilization by high molecular weight
organic compounds
• Flooding incorporates Zn into iron
compounds and increases pH
Zinc availability in soils
increases with:
a) decreasing soil pH
b) increasing CaCO3 content
c) liming
d) flooding
d) all of the above
Copper and Manganese
• Immobile in soils and plants
• Cu is very strongly complexed by soil
organic matter and specifically adsorbed by
layer silicates
• Solubility of Cu and Mn increases 100 folds
for each unit decrease in pH
Copper Sources
• Swine manure is high in Cu
• Copper sulfate, copper acetate, and copper
ammonium phosphate are common sources
of Cu
• Soil applications at rates of 1 to 20 lb/acre
• Foliar applications for emergency
Copper deficiency
Mn in Soils
• Mn2+ in reduced soils and Mn4+ in oxidized
soils
• Mn becomes available by reduction and
chelation
• Mn is immobile in soils and plants
Micronutrient Anions
• Boron absorption as H3BO3
• Molybdenum is absorbed as MoO42• Chlorine absorbed as Cl-
Molybdenum in Soils
• Total Mo in soils range from 0.2 to 5 ppm
• Soil solution concentrations < 4ppb
• Solubility increases 10 fold for each unit
increase in pH
• P enhances Mo uptake and sulfate reduces
Mo uptake
• Both Cu and Mn reduce Mo uptake
Boron
• Mobile in soils, immobile in plants
• Adsorbed on iron oxides and calcium
carbonates
• Complexed with organic matter
• Boron becomes less available above pH 6.3
to 6.5
• Liming strongly acid soils may cause
temporary B deficiency
MIRACLE
FERTILIZERS!
Usually contain micronutrients,
and
That’s what makes them magical!
Conclusions
• All micronutrients are immobile in plants
• A very narrow range between deficiency
and toxicity
Conclusions
• In general, the metals (Fe, Cu, Mn, and Zn)
are more available at lower pH.
• The anions (B, Mo, Cl) are available at
higher pH.
• The keys to proper micronutrient
availability are:
moderate pH
maintaining Organic Matter content
Which micronutrients are taken
up by plants as anions?
a) Fe, Cu, Mn, Zn
b) B, Mo, Cl
Which statement regarding Mo
is false:
a) Mo in soils is adsorbed by
plants as MoO42b) Excessive Mo is toxic to
grazing animals
c) Mo is more available at low
pH
Which of the following lists the
universally accepted essential
micronutrients?
a) Fe, Mn, Cu, Zn, Cd, B, Mo
b) Fe, Mn, Al, Si, Se, Cl, Mo
c) Fe, Mn, Cu, Zn, B, Cl, Mo
d) Fe, Mn, Cu, B, Cl, Se, As
What are important factors to ensure
that micronutrient deficiencies are
unlikely to occur?
a) maintaining moderate pH
b) having adequate levels of OM
c) fertilizing with NPK
d) using manures
e) growing rice
How do chelates change micronutrient
availability?
a) they release micros through OM
decomposition because they are soluble
organic molecules
b) they decrease them by adsorbing micros
c) they increase them because they raise pH
e) no effect, but they run fast
Which percentage of students is
most likely to miss a
micronutrient question on the
test?
a) 28%
b) 50%
c) 94%
d) 100%