phosphorus nutrition of wheat. outline: p nutrition of wheat 1.what are the nutrient requirements of...

Phosphorus Nutritionof Wheat

Outline:P Nutrition of Wheat

1. What are the nutrient requirements of wheat throughout the season?

2. Why is P needed early in the season?

3. Why is placing P near the seed important?

4. How can I be sure there are adequate supplies of P?

5. What are some good strategies for managing P?

Photo courtesy of the USDA-ARS

What have the trends been in wheat yield?

NASS; Statistics Canada

0.31 bu/A/yr

0.38 bu/A/yr

10

15

20

25

30

35

40

45

1960 1965 1970 1975 1980 1985 1990 1995 2000 2005

Year

Whe

at y

ield

, bu

/A

Canada

U.S.

What are the nutrient requirements of wheat throughout the season?

Photo courtesy of the USDA-ARS

Plants take up P as:

• Primary orthophosphate ion: H2PO4- (pH < 7.0)

• Secondary orthophosphate ion: HPO4= (pH > 8.0)

• The form most common is a function of soil pH – both equally present at neutral

Solution P

How much N, P, and K does wheat take up?

0

20

40

60

80

100

120

140

emer

gence

tille

ring

flag le

af

headin

g

anth

esis

early

milk

soft

dough

harve

st

Nut

rient

upt

ake,

lb/A

N

K2O

P2O5

38 bu/A spring wheat

Growth stage

Johnston et al., 1999

How are nutrients distributed in the plant?

Grain Straw

0

20

40

60

80

100

120

N P2O5 K2O

Nut

rient

con

tent

, lb

/A

Crop Removal 0.5 – 0.6

lb P2O5/bu

38 bu/A spring wheat

Johnston et al., 1999

How is P distributedin the plant?

Miller et al., 1994

Percent at physiological maturity:

16.01.8 15.07.0 10.2 11.5 14.04.5Haun**

80

9

830

10

20

30

40

50

60

139 319 499 679 859 1039 1219 1399 1579 1759GDD*

Leaves

Stem

Head

Grain

Cum

ulat

ive

P u

ptak

e,lb

P2O

5/A

90 bu/A irrigated spring wheat

* Growing degree days ** Haun growth stage

What percent of the Pin the plant comes from fertilizer?

Mitchell, 1957

0

50

100

150

200

250

300

4 weeks heading soft dough mature

Tot

al P

upt

ake,

mg

Unfertilized

Fertilized with MAP

46 %

43 %

36 %

39 %

Stage of growth

Why is P neededearly in theseason?

Early season P nutritionis critical

• Early season P deficiencylimits yield potential

– Critical period:first 5 to 6 weeks

– P has major impacts ontillering and rooting

• Wheat absorbs only 15%of total P uptake in firsttwo weeks of growth

– Small amount but critical for optimum yield– Reserves can support later growth

• Later season P stress has much lower impact oncrop production

Photo courtesy of the USDA NRCS

Wheat tillers

• Wheat producestwo kinds of stems (culms):

– Main stem– Variable number of tillers

• Tillering is not a random event• Follows a very strict pattern• Tillers initiated vary greatly

in vigor and potentialfor grain production

Wheat Plant

Nodal roots

Seminal roots

Seed

ColeoptiletillerT0

SecondtillerT2

SecondleafL2

FourthleafL4

FifthleafL5

ThirdleafL3

FirstleafL1

FirsttillerT1

Goos and Johnson, 1996; Klepper et al., 1982

Contribution of tillersto yield

Goos and Johnson, 1996

0

10

20

30

40

50

60

Main stem T1 + T2 Other

Per

cent

of

final

yie

ld

SecondtillerT2

Mainstem

FirsttillerT1

Spring WheatEmbden, ND – 46 bu/A

Spring WheatEmbden, ND – 46 bu/A

Phosphorus increases tiller initiation


0

10

20

30

40

50

60

70

80

90

100

T0 T1 T2 T3 T4 ST

Per

cent

initi

atio

n

0

30

lb P2O5 /A placed with the seed

Tillers

Hettinger, NDOlsen P = 10 ppm

Hettinger, NDOlsen P = 10 ppm

Why is placing Pnear the seedimportant?

10 lb of starterP2O5 with seed

No starter P

Impact of a Cool Spring on Spring Wheat’s EmergenceBoth sides received fall-banded 70-30-10-10

Root development:1-2 leaf stage

Winter wheatWinter wheat

Veseth et al., 1986

0

2

4

6

80246 2 4 6

Distance from the seed row, in.

Dep

th,

in.

Primary root

First seminal pair

Crown

Rooted soil volume

Root development:4 leaf stage, 1 tiller

0

2

4

6

80246 2 4 6

Distance from the seed row, in.

Dep

th,

in.

Crown

Second seminal pairFirst crown root

First seminal pair

Winter wheatWinter wheat

Veseth et al., 1986

The primarycause oflow, shortterm uptakeof Pfertilizer:

The inability of P to moveto absorbing roots

Pla

nt r

oot

Higher Pconcentration

Lower Pconcentration

Diff

usio

n

Spring wheat rootsat 38 days

• Based on average root density in surface 6”

0.12”P diffusion zone

Root

0.5”Distance between roots

5% of soil volume can contribute P to the plant


Spring wheat rootsat 94 days

• Based on average root density in surface 6”

0.13”

P diffusion zone

0.24”Distance between

roots



Root

Is P near the seed important at higher soil test P levels?

Year – site: 95-1 95-2 96-1 96-2 96-3 95-3 96-4 95-4

T1

+ T

2 til

ler

initi

atio

n,nu

mbe

r/pl

ant

0.0

0.4

0.8

1.2

1.6

2.0

Control

20 lb P2O5/A applied with the seed as 10-34-0

Olsen P, ppm: 6 9 10 13 13 1687

Goos and Johnson, personal communication

Is P near the seed important at higher soil test P levels?


95-1 95-2 96-1 96-2 96-3 95-3 96-4 95-4

Spr

ing

whe

at y

ield

, bu

/A

0

10

20

30

40

50

60

70 Control

Olsen P, ppm: 6 9 10 13 13 1687

Year – site:

20 lb P2O5/A applied with the seed as 10-34-0

How can Ibe surethere areadequatesuppliesof P?

Photos courtesy of the USDA NRCS

What information does a P soil test provide?

• An index of the amountof plant-available P inthe soil

• This index must becalibrated to yieldresponse:

– Examine responses to Padditions at various soil test levels

– Conduct studies across a wide rangeof soil test levels and environmental conditions

How is a soil test calibrated to yield response?

Gelderman et al., 1995

% relative yield for this site-year:39 bu/A

73 bu/AX 100 = 53.4%

Watertown Site 1995Olsen P = 5.0 ppm

0

10

20

30

40

50

60

70

80

0 20 40 60 80 100

Fertilizer P, lb P2O5/A

Win

ter

whe

at y

ield

, bu

/A

Crop responses at various soil test levels

0 20 40 60 80 10030

45

60

75

90

105

P2O5 rate, lb/A

Spr

ing

whe

at y

ield

, bu

/ASoil test P

(ppm)

4 Hauberg (Irr.)

19 Tullis (Irr.)

12 Riley (Irr.)

5 SIDC (Irr.)

6 Kent (Irr.)

3 Hauberg (dry-Fallow) 4 Hauberg (dry-Stub.)

Henry and Gares, 1993

Average level of yield response is related to soil test P

Soil type Soil test PYield

Increase

(ppm) (%)

Hauberg (dry) 3 93

Hauberg (Irr.) 4 43

Hauberg (S) 4 65

SIDC 5 65

Kent 6 17

Riley 12 27

Tullis 19 5

Henry and Gares, 1993

Average level of yield response is related tosoil test P• As soil test levels

increase, the magnitude of yield response to added P decreases

Mitchell, 1932

90

Yie

ld in

crea

se,

%r = - 0.68

0 10 20 30 40 50 60

Soil test P, ppm

80

70

60

50

40

30

20

10

0-10-20

How is a soil test calibrated to yield response?

120

Gelderman et al., 1996 Olsen P, ppm

Win

ter

whe

at r

elat

ive

yiel

d, %

0 5 10 15 20 25 30 350

20

40

60

80

100

Watertown 1995

Critical level = 16 ppm

Several sitesand years

Several sitesand years

Accuracy in response predictions is limited

Winter wheat study site

Phosphorus Ideal Watertown

rate 4.5 ppm 5.0 ppm

(lb P2O5/A) ------------ (bu/A) -----------

0 33 39

25 32 49

50 34 45

75 31 56

100 32 73

Responsive? No Yes

Gelderman et al., 1996

Examples of Pcalibration data

• Calibration curve indicates which soil test levels tend to limit yields

• Data based on P responses observed across several sites and years

McKenzie et al., 1995

Norwest P, ppm

Rel

ativ

e yi

eld,

%

Prairie soils

one site-year

40

50

60

70

80

90

100

10 20 30 40 50 60 700

Examples of Pcalibration data

PPI, PKMAN Ver. 1.0

30

40

50

60

70

80

90

100

0 5 10 15 20 25 30

Olsen P soil test level, ppm

Rel

ativ

e yi

eld,

%

Winter wheat, Kansas

Spring wheat, Northern Great Plains

What are the best uses for soil test P information?

— Estimating average probabilities of crop response

— Examining changes in levels over time

— Estimating average relative yield response

— Estimating a specific probability of response for a given site and year

— Estimating a specific relative yield response at a given site and year

Good

Fair

Poor

What are somegood strategies for managing P?

Photos courtesy of the USDA NRCS

Approaches to P fertilization

• Sufficiency approach:Apply P to maximizenet returns to fertilizationin the year of application

– Strategy: fertilize onlywhen there is a goodchance that a profitableyield response will be realized

– Soil test levels kept in lower,responsive ranges

– Normally adopted on land leasedfor short periods of time or when cash flow is limited

Rel

ativ

e yi

eld

, %

Soil test P level

Approaches to P fertilization

• Build and maintenanceapproach:Remove P as ayield-limiting variable

– Strategy: apply extra P(more than expectedcrop removal) to buildsoil tests to levels thatare not yield-limiting

– Soil test levels kept in higher,non-responsive ranges

– Normally adopted on owned land or land leased for longer periods of time

Rel

ativ

e yi

eld

, %

Soil test P level

Can annual fertilizer applications match higher fertility?

Annual seed-placed P2O5, lb/A

0 10 20 30 4028

30

32

34

36

38

40

42

Whe

at y

ield

, bu

/A

5 ppm

8 ppm

15 ppm

Amount broadcast initially, lb P2O5/A

160

80

0

Olsen soil testat end of 5-yr:

Wager et al., 1986

N rate, lb/AP2O5 rate,lb/A

Winter wheatyield, bu/A

11055

00

2040

0

10

20

30

40

50

60

70

How do N and P interact?

Grant et al., 1985; Grant et al., 1986

64.8

54.8

47.946.7

42.341.7

20.4

17.0

14.6

6 bu:40% increase

5 bu:12% increase

17 bu:35% increase

$0.22$0.27

$0.32$3.00

$4.00$5.000.00

1.002.003.00

4.005.00

6.00

7.00

8.00

9.00

P2O5 price, $/lbWinter wheat

price, $/bu

Net returnto P

fertilization,$/A

How do crop and nutrient prices impact profit?

$8.60

$6.82

$5.60

$6.68

$5.26

$4.28$4.76

$3.69

$2.96

110 lb N/A40 lb P2O5/A

110 lb N/A40 lb P2O5/A

Grant et al., 1985; Grant et al., 1986

Does P fertilizer form influence crop response?

• Research evaluating crop response to MAP, DAP and APP have found all sources give equal crop response

• In addition, no agronomic differences have been found between dry and liquid sources

• The only exception is rock phosphate which provides limited crop response due to low P solubility

Fixen, 1989; Leikam, 1990

How much is saved the first year if P is applied below recommended rates?

If you cut the rate by:

*Fertilizer cost

savings:

(lb P2O5/A) ($/A)

5 1.25

10 2.50

20 5.00

40 10.00

* $0.25/lb P2O5



*Fertilizer cost

savings:

**Interest on money saved:

(lb P2O5/A) ----------- ($/A) -------------

5 1.25 0.13

10 2.50 0.25

20 5.00 0.50

40 10.00 1.00

* $0.25/lb P2O5

** 10% real interest rate (after inflation rate has been subtracted), compounded annually, 12 month term



*Fertilizer cost

savings:


Total savings (fertilizer cost +

interest)

(lb P2O5/A) -------------------- ($/A) ------------------------

5 1.25 0.13 1.38

10 2.50 0.25 2.75

20 5.00 0.50 5.50

40 10.00 1.00 11.00

* $0.25/lb P2O5




*Fertilizer cost

savings:


Total savings (fertilizer cost +

interest)

***Maximum allowable yield

reduction

(lb P2O5/A) -------------------- ($/A) ------------------------ (bu/A)

5 1.25 0.13 1.38 (0.3)

10 2.50 0.25 2.75 (0.7)

20 5.00 0.50 5.50 (1.4)

40 10.00 1.00 11.00 (2.8)

* $0.25/lb P2O5


*** $4.00/bu wheat

What does it cost the first yearif P is applied aboverecommended rates? (one-year lease)

If you over-apply by:

*The lost principle is:

**The lostinterest is:

Total cost (principle +

interest)

***Yield equivalent of

total cost

(lb P2O5/A) -------------------- ($/A) ------------------------ (bu/A)

5 (1.25) (0.13) (1.38) (0.3)

10 (2.50) (0.25) (2.75) (0.7)

20 (5.00) (0.50) (5.50) (1.4)

40 (10.00) (1.00) (11.00) (2.8)

* $0.25/lb P2O5


*** $4.00/bu wheat

What happens to fertilizer P after I apply it?

• Solution P:– 10 to 30 % of applied P– Immediately available

Solution P Labile P Non-labile P

• Labile P:– 70 to 90% of applied P– Future supply– Metastable Ca-phosphates

What does it cost the first yearif P is applied aboverecommended rates? (five-year lease)


*The lost interest is:

(lb P2O5/A) ($/A)

5 (0.13)

10 (0.25)

20 (0.50)

40 (1.00)

* 10% real interest rate (after inflation rate has been subtracted), compounded annually




**The depreciation is:

(lb P2O5/A) ----------- ($/A) -----------

5 (0.13) (0.08)

10 (0.25) (0.15)

20 (0.50) (0.30)

40 (1.00) (0.60)


** 30% of applied P not recovered after five years (30% depreciable base with five-year economic life, straight line depreciation, $0.25/lb P2O5)





Total cost: (interest plus depreciation)

(lb P2O5/A) ---------------------- ($/A) ---------------------------

5 (0.13) (0.08) (0.21)

10 (0.25) (0.15) (0.40)

20 (0.50) (0.30) (0.80)

40 (1.00) (0.60) (1.60)







Total cost: (interest plus depreciation)

***Yield equivalent of total loss

(lb P2O5/A) ---------------------- ($/A) --------------------------- (bu/A)

5 (0.13) (0.08) (0.21) (0.05)

10 (0.25) (0.15) (0.40) (0.1)

20 (0.50) (0.30) (0.80) (0.2)

40 (1.00) (0.60) (1.60) (0.4)



*** $4.00/bu wheat

Over-applying vs. under-applying (five-year lease)


Yield equivalent of

total loss:If you under-

apply by:

Maximum allowable yield

reduction

(lb P2O5/A) (bu/A) (lb P2O5/A) (bu/A)

5 (0.05) 5 (0.3)

10 (0.1) 10 (0.7)

20 (0.2) 20 (1.4)

40 (0.4) 40 (2.8)



*** $4.00/bu wheat

Summary

• P nutrition is critical to reaching the attainable yield potential of wheat

• Early in the season when the wheat plant is “deciding” to initiate tillers, P must be positionally available

• P deficiencies earlier in the season are more detrimental than those occurring later

• P nutrition must be part of a management strategy that considers the importance of other nutrients

• Land ownership/rental and cash flow have a large impact on the approaches taken to managing soil fertility

For more information, contact:

International Plant Nutrition Institute (IPNI) 655 Engineering Drive, Suite 110Norcross, GA 30092-2604Phone: 770-447-0335; Fax: 770-448-0439www.ipni.net

Reference 06128

phosphorus nutrition of wheat. outline: p nutrition of wheat 1.what are the nutrient requirements of...

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