Transcript Nitrogen and Sulfur

Nitrogen and Sulfur
18 Essential Elements
Macronutrients:
Carbon (C)
Hydrogen (H)
Oxygen (O)
Nitrogen (N)
Phosphorus (P)
Potassium (K)
Micronutrients:
Iron (Fe)
Manganese (Mn)
Boron (B)
Zinc (Zn)
Copper (Cu)
Chlorine (Cl)
Calcium (Ca)
Magnesium (Mg)
Sulfur (S)
Cobalt (Co)
Molybednum (Mo)
Nickel (Ni)
Plant Available
Forms of Nitrogen
NH4+
Ammonium
NO3-
nitrate
Which form is cation/anion?
Which form held by clay and humus?
Which form do plants prefer?
Which form leaches?
Importance of Nitrogen
in Plant Nutrition
Stimulates vegetative growth
Gives deep green color to leaves
Component of:
1. chlorophyll and enzymes
2. amino acids
3. nucleic acids
Too Much Nitrogen
Encourages soft, weak, easily injured
growth.
May slow maturity and ripening of crops
May delay “hardening-off” process that
protects plants from winter cold.
Plants may accumulate high levels of
nitrate which can be toxic to cattle
(sorghum spp.)
Nitrogen Deficiency in Corn
Chlorosis (yellowing) at the tip and midrib of the oldest
leaves.
Nitrogen Is Mobile in the Plant
 Because N is mobile in the
plant… the deficiency
symptoms will shop up first
on OLDER leaves.
Nutrients that are
Mobile and Immobile in Plants
mobile
immobile
Nitrogen
Deficiency
Waterlogged soil resulted in nitrogen loss by denitrification and leaching.
Waterlogged soils and
N deficient corn
THE NITROGEN CYCLE
Atmospheric N2
Denitrification
N2 and N2O gas
Fertilizers
Precipitation
Biological N
Fixation
Ammonia
Volatilization
NH3 gas
soil
-
NO3
nitrate
leaching
nitrification
NH4+
ammonium
Nitrogen Cycle
Main reservoir of nitrogen is atmospheric
air (78% of air is N2)
As N moves through the Nitrogen Cycle,
an atom of N may appear in many
different chemical forms. (N2 , NH4+, NO3-)
N cycle has a gas phase and a mineral
phase.
Nitrogen “Fixed” By:
1. Biological Organisms
• EX: Rhizobium bacteria / legumes
2. Lightning
• Lightning strike “fixes” some nitrogen which comes down in rain.
• adds approx. 1-20 lb per acre annually
3. Nitrogen fertilizers
• N containing synthetic fertilizers
• bypasses "natural" N fixation
Immobilization & Mineralization
Immobilization – conversion of “mineral ”
forms of nitrogen to “organic” forms
− Mineral forms like NH4+ and NO3- are taken up by plants
and incorporated into organic molecules.
Mineralization – the conversion of “organic ”
forms of nitrogen back to “mineral” forms.
Nitrogen & Organic Matter
 Plants utilize N as ammonium (NH4+ ) or nitrate
(NO3-)
 More than 95% of the total nitrogen in the soil is
immobilized in OM and released slowly.
 Soil with 1% OM contains about 2,000 lbs N; but
only about 1% mineralizes annually and becomes
available for plants (~20 lbs).
 OM decomposition and release of N proceeds most
quickly in warm, well-aerated, moist soils
NITRIFICATION
Conversion of ammonium to nitrate.
Oxidation accomplished by certain bacteria
species in the soil
2 step process:
Nitrobacter
NH4+
ammonium
Nitrosomonas
NO2nitrite
NO3nitrate
DENITRIFICATION
anaerobic bacteria
NO3-
N20
nitrate
nitrous
oxide gas
+
N2
dinitrogen
gas
 Conversion of nitrate to gaseous nitrogen forms.
 Occurs when insufficient oxygen in the soil
(i.e. soils waterlogged)
 anaerobic bacteria forced to use the nitrogen in
NO3- as an electron acceptor (normally O2 is used).
 Rapid loss of nitrogen in warm, waterlogged soil
 Average 10-20% of nitrates lost... But losses can
be as much as 40-60%.
Waterlogged soil resulted in nitrogen loss by denitrification and leaching.
AMMONIA VOLATILIZATION
 Loss of nitrogen as the gas ammonia (NH3)
 Occurs when ammonium loses a H+ in alkaline
soils and becomes a gas
NH4+ + OH-
NH3 + HOH
 Losses occur from surface applications of urea
and ammonium fertilizer.
 N loss for urea around 30% if not incorporated
by tillage, rain, or irrigation within 72 hours
Fertilizer Guarantee (Grade)
%N - %P2O5 - %K2O
1. % Total Nitrogen
2. % Available Phosphorus, calculated as P2O5
3. % Water-soluble Potassium, calculated as K2O
-- Historically, P and K reported as the oxide form.
-- Resistance to change because if reported as elemental
form the grade would be lower
Example: Triple super phosphate 0-45-0 is only
0-19-0 if reported as %P rather than % P2O5.
-- 4th number sometimes included is % S.
The Most Common
Nitrogen Containing Fertilizers
• Anhydrous ammonia 82-0-0
• Urea 46-0-0
• Ammonium nitrate 34-0-0
•
•
•
•
•
Ammonium sulfate 21-0-0-24S
UAN 28-0-0 or 32-0-0 (liquid)
Ammonium polyphosphate 10-34-0 (liquid)
MAP 11-52-0
DAP 18-46-0
Manage Nitrogen
according to Yield Goal
 Nitrogen requirement changes with yield:
30 bushel wheat = 60 lbs N/acre
60 bushel wheat = 125 lbs N/acre
100 bushel wheat = 240 lbs N/acre
 Soil test to determine what you currently have…
then add the difference to insure adequate N for
your yield goal
Manage Nitrogen
according to Yield Goal
General Rules-of-Thumb for Wheat
2 lb N per bushel of wheat grain
60 lb N per ton of wheat forage (hay).
- 15 lb N/stocker per month grazing.
- 30 lb N/acre per 100 lbs beef produced
SULFUR
Importance:
 Found in 3 amino acids:
Methionine, Cysteine, Cystine
 Needed for making chlorophyll
 Found in vitamins and oils
 Important in plant metabolism
SULFUR
Healthy plant foliage generally contains
1/10th as much sulfur as nitrogen.
5 to 15 lb/acre usually adequate
Sulfate ion (SO42-) is form used by plants
 SO42- is an anion and easily leached
Natural Sources of Sulfur
Organic matter
• 70-90% of soil sulfur is in OM
Soil minerals
• arid soils ─ gypsum CaSO4
• iron pyrite “fools gold” FeS2
Natural Sources of Sulfur
Atmospheric sulfur
• Air pollutant from burning coal and oil.
• Pollution can supply ½ of plants sulfur requirements.
• 2-8 lb/A sulfur added to soil annually from rain in
Oklahoma… more in E
• Irrigation water can also be high in sulfate
• Irrigation water containing 1 ppm sulfate adds
2.7 lbs S per acre for
each acre-foot of irrigation
Sulfur Deficiency Symptoms:
Chlorosis in NEW leaves (immobile in plant)
Growth reduction, but not
as dramatic as with N.
Corn, sorghum, cotton
high demand for S
Sulfur Deficiency
Much of the soil’s sulfur has been used up
by high yielding crops over the last 50 years
and has not been replaced.
Sulfur content of today’s preferred fertilizers
are low.
Atmospheric sulfur dioxide pollution has
diminished.
Sandy and low OM soils most prone to S
deficiencies
Sulfur Deficiency in Corn
Overall light green color, worse on new leaves during rapid growth.
Sulfur Deficiency in Wheat
Overall light green color, worse on new leaves during rapid
growth.
Similarities of N & S
1. Both held largely in OM
2. Both released as inorganic ions (SO42-,
NH4+, NO3-); release accomplished by soil
microorganisms
3. Anaerobic soil organisms change these
elements into gaseous forms.
4. Each have a form that is easily leached
(NO3- and SO42-)
Common Sulfur Fertilizers
Material
%S
Elemental sulfur
90
Ammonium sulfate
24
Ammonium thiosulfate
26
Ordinary superphosphate
12
Potassium sulfate
17
Gypsum
17
Sulfate of potash, magnesia
22