Phosphorus Cycle

Front 1

4 Deficiency symtoms of phosphorus

Back 1

1. stunting
2. thin-stimmed
3. spindly appearance
4. purple spots in leaves

Front 2

True or False? Most P in soil is readily available to plants

Back 2

False:
slowly or not available to plants
<0.03 mg/L in the soil

Front 3

Phosphorus Sources

Back 3

Mineral – apatite [rock phosphate,
Ca5(OH,F,Cl)(PO4)3]
• Plant residue ~ 0.2 to 0.4%
• Animal residue ~ 0.5 to 4%
• Desorption from hydrous Fe and Al oxides
(sesquioxides) and silicate clays
• Fertilizer

Front 4

Fertilizer

Back 4

– Made from rock phosphate
– React rock phosphate with sulfuric acid
– By product gypsum has traces of U238 (4.5x109yr) and
Ra226 (1620yr) [half-lives given in ( )].

Front 5

Phosphorus Losses

Back 5

Crop removal/uptake
• Erosion and surface runoff
• Minimal leaching losses except where soil
is sandy or where P added as organic rather
than inorganic source
• Fixation with Al and Fe (forms the minerals
variscite and strengite, respectively)
• Reversion back to apatite in Ca-rich soils
Immobilization: Inorganic to organic P
• Adsorption to Fe and Al hydrous oxides and
silicate clays
• Occluded P

Front 6

P Soil Characteristics

Back 6

Main problem is most P in soil is not plant
available
• P form is pH dependent
• P does not undergo oxidation-reduction
• H2PO4
- HPO4
2- + H+ pKeq = 7.20
• Thus, at pH’s > 7.20 HPO4
2- dominates and
at pH’s < 7.20 H2PO4
- dominates

Front 7

P Characteristics cont.

Back 7

In acid soils H2PO4
- and HPO4
2- react
mainly with Al and Fe, possibly Mn and
become insoluble
• In alkaline soils H2PO4
- and HPO4
2- react
mainly with Ca and possibly Mg and
become insoluble
• Best pH range between 6 and 7

Front 8

Factors Affecting P
Solubility/Availability

Back 8

Soil pH
• Organic matter content and mineralization rate
• Source of P – organic vs. inorganic (0-13-0)
• Mineral sources of P – particle size and solubility
• Amount of Ca, Fe, Al, etc. available to react with
P. Also the mineralogy of clay-sized particles
• Soil temperature, moisture for mineralization

Front 9

Soil Management for Phosphorus

Back 9

• Maintain pH between 6 and 7
• Maintain high OM level and good
conditions for microbial activity during
growing season
• Perhaps only 1/3 of applied P is used the
year of application - next year, residual P
may be significant. More residual P
available if pH 6-7, and if clay is 2:1 types.
• Soil sampling and stratificaiton

Front 10

Soil Management for P, cont.

Back 10

Addition of P at agronomic rates

Front 11

Addition of P at agronomic rates

Back 11

– May need to apply yearly; may have some
carry-over effect (residual P from prior year)
– Banding reduces reversion and fixation
• Banding or injecting fertilizer below and/or to side
of seed at planting

Front 12

Soil Management for P, cont.

Back 12

• Usually see P deficiencies early in spring, may
grow out of it when temperature increases
• P deficiency symptoms – purpling of leaf; general
stunting, spindly growth
• Soil test extractions regional based upon pH,
correlated to plant uptake and yield

Front 13

• Soil test extractions regional based upon pH,
correlated to plant uptake and yield

Back 13

– Acid soils: Bray I, Bray II, Mehlich I and II
– Alkaline soils: Olsen
– Acid/alkaline: TAMU, Mehlich III

Front 14

Sources of Nutrients
Nitrogen

Back 14

• All made from atmospheric N2

Front 15

All made from atmospheric N2

Back 15

anhydrous ammonia: NH :
N N
– NH3: 82-0-– ammonium nitrate: NH4NO3:
– urea: (NH2)2CO:
– ammonium sulfate: (NH4)2SO4:
– UNA: liquid
combination of urea and
ammonium nitrate

Front 16

Sources of Nutrients, cont.

Back 16

• P (made from rock phosphate, apatite)
• K (mined from evaporite deposits)
• Solid vs Liquid…Custom-blended vs
packaged.

Front 17

P (made from rock phosphate, apatite)

Back 17

– monoammonium phosphate: NH4H2PO4:
– diammonium phosphate: (NH4)2HPO4:
– triple superphosphate: Ca(H2PO4)2:

Front 18

K (mined from evaporite deposits)

Back 18

– potassium chloride (sylvite): KCl

Front 19

5 Sources of Nutrients
Nitrogen

Back 19

1. All made from atmospheric N2
2. P (made from rock phosphate, apatite)
3. K (mined from evaporite deposits)
4. Solid vs Liquid
5. Organic

Front 20

All made from atmospheric N2

Back 20

-anhydrous ammonia: NH3
-ammonium nitrate: NH4NO3
– urea: (NH2)2CO
– ammonium sulfate: 2(NH4) SO4
– UNA

Front 21

P (made from rock phosphate, apatite)

Back 21

– monoammonium phosphate:
– diammonium phosphate
– triple superphosphate

Front 22

K (mined from evaporite deposits)

Back 22

potassium chloride (sylvite):

Front 23

Solid vs Liquid

Back 23

Custom-blended vs
packaged.

Front 24

Organic

Back 24

animal manures
biosolids
dried blood
bone meal
cottonseed meal

Front 25

Plant content
N - %
P - %
K - %

Back 25

N - 3%
P - 0.3%
K - 2%

Front 26

anhydrous ammonia

Back 26

NH3 : 82 -0 -0

Front 27

ammonium nitrate

Back 27

NH4 NO3 : 33-0-0

Front 28

urea

Back 28

(NH2)2 CO: 45-0-0

Front 29

ammonium sulfate

Back 29

(NH4)2SO4: 21-0-0-23(S)

Front 30

UNA

Back 30

liquid 32-0-0 combination of urea and ammonium nitrate

Front 31

monoammonium phosphate

Back 31

NH4H2PO4:
11-48-0

Front 32

diammonium phosphate

Back 32

(NH4)2HPO4: 1
8-46-0

Front 33

triple superphosphate

Back 33

Ca(H2PO4)2:
0-46-0

Front 34

potassium chloride

Back 34

(sylvite):
KCl:
0-0-60

Front 35

animal manures

Back 35

N- 0.5 to 4: P- 0.3 to 5:
K- 0.3 to 4:
ratio usually close to 1-1-1

Front 36

biosolids

Back 36

N- ~5:
P- ~1:
K- ~0.1

Front 37

dried blood

Back 37

12 to 15 -3-1

Front 38

bone meal

Back 38

4-21-0.2

Front 39

cottonseed meal

Back 39

6 to 7 -2.5-1.5

Front 40

Nutrient Application

Back 40

1. Application methods
2. Timing
3.

Front 41

Application methods (5 types)

Back 41

1. broadcast and incorporation
2. banding
3. injecting
4. foliar
5. Fertigation

Front 42

Timing consider (5 things)
(Nutrient Application)

Back 42

1. leaching potential,
2. anaerobic
3. conditions,
4. erosion/runoff,
5. plant needs

Front 43

Nutrient Management (2)

Back 43

Soil test recommendations

Plant tissue analyses

Front 44

Soil test recommendations
#1

Back 44

1. Developed by state
extractant correlated with
extracted amount and yield

Front 45

Soil test recommendations
#2

Back 45

Most Land Grant Universities use philosophy of
“sufficiency”

Front 46

Soil test recommendations
#3

Back 46

Most commercial labs use philosophy of “build up and maintain”

Front 47

Fertilizer Cost

Back 47

Depends upon the kind and source of fertilizer nutrients in the material

Front 48

Fertilizer Cost can be expressed as-

Back 48

cost per fertilizer unit,
cost per pound,
cost per 100 pounds of nutrients

Front 49

“unit of fertilizer”

Back 49

is 20 pounds of nutrient (N
and P2O5 and K2O).
(A unit is 1% of nutrient
in a ton of fertilizer).

Front 50

Calculate the cost of 13-13-13 on a pound of nutrient basis if a 50 pound bag costs
$9.95.

Back 50

Answer: $0.51
Suggest you review pp. 36-40
in the lab

Front 51

Calculate the price per pound of nutrients for cottonseed meal. Assume a label of 6.5-2.5-1.5. The cost of a 50 pound bag is$5.75.

Back 51

Answer: $1.10

Front 52

Calculate the amount of K+ in a 10 pound
bag of fertilizer that is labeled as 22-4-18.

Back 52

Answer: 1.49 lbs

Front 53

Precision Agriculture

Back 53

1. Soil sampling on 1 to 5 A grids instead of~40A
2. Yield monitoring equipment
3. Variable rate planting, fertilizer and pesticide equipment

Front 54

Nutrient Management Tools

Back 54

1. Natural Resources Conservation Service
2. Texas State Soil and Water Conservation Board

Front 55

Natural Resources Conservation Service

Back 55

-Nutrient Management Plan

-Must be a Certified Nutrient Management Specialist (CNMS) to approve through short course

Front 56

Texas State Soil and Water Conservation Board

Back 56

– Water Quality Management Plan
– Must be CNMS to approve

Front 57

Certification Opportunities

Back 57

• Certified Nutrient Management Specialist

• Certified Professional Agronomist

• Certified Professional Soil Scientist

• Certified Crop Advisor
• Professional Geoscientist (Soil Scientist)