Phosphorus Nutritionof Alfalfa

Phosphorus (P) Nutritionof Alfalfa

• U.S. alfalfa hay yields keep increasing

• Nutrient uptake and removal

• Alfalfa root development

• General P nutrition

• P boosts hay yield, recovery, and quality

• P inputs: frequency and source

• Requirement for balanced nutrition

Outline:

U.S. Alfalfa Hay Yields…An Upward Trend

Year

Source: USDA-NASS

2

2.5

3

3.5

4

1970 1975 1980 1985 1990 1995 2000

Yie

ld,

ton

/A

Record Yield:Researchers at University of Arizona(Yuma) set record for alfalfa yieldin a year:24.1 tons/A alfalfa hay in10 cuttings

• Optimal and uniform irrigation• Chopped hay removed immediately after cutting• N fertilizer regularly added – was it needed?

• 460 lb P2O5/A added before planting

• K management unknown

• 1,440 lb K2O and 360 lb P2O5/A removed in hay

Ludwick, 2000; Arizona

Alfalfa Nutrient Uptakeand Removal

• Alfalfa has higher demandfor nutrients than most crops

NutrientAmount

Removed

lb/ton

P2O5 15

K2O 60

Ca 30

Mg 6

S 6

N (through fixation) 60

Alfalfa Root Development

• Most lateral roots are near the soil surface for the first year, but more deep lateral roots develop as the plant ages

• Alfalfa has lower root density than many grasses and a deeper rooting zone

• P and K application increase root growth, enabling roots to obtain moisture and nutrients from greater volume of soil

Available P

Unavailable P

Phosphorus in Soils

• Total P in many soils (0 to 6 in.) ranges from 400 to 2,000 lb/A…but only a fraction of that is available for plant uptake each season

The primary cause of low, short-term uptakeof P fertilizer:• The inability of P to move

to absorbing roots

Pla

nt r

oot

Higher Pconcentration

Lower Pconcentration

Diff

usio

n

Adequate P is essential for strong root systemsHigher levels of nutrients are needed to support vigorous

plant growth in cool soil conditions

Temperature Effect on Nutrient Uptake

Cool soil temperatures will:

• slow nutrient release from soil organic matter

• reduce diffusion of nutrients to the roots

• hinder root absorption and translocation

P Functions in Plants

• Energy storage and transfer– Phosphate compounds are “energy currency”

– (such as ADP and ATP)

• Structural component of biochemicals– Seed formation

– Calcium and magnesium phytate

• Maintenance and transfer of genetic code

• Root growth, rapid crop establishment

• Early maturity, quicker recovery

P Fertilization Increases Nodulation

Azcon et al., 1988

0

50

100

150

200

250

300

75% 90% 100%

4.510.315.621.8

Soil P, ppm

Nu

mb

er o

f n

od

ule

s

Soil water holding capacity

P Fertilization Increases Nodule Growth

Gates, 1974

0 64126

254

510

0

100

200

300

400

500

600

P application, lb P2O5/A

Nod

ule

dry

wei

ght,

mg/

plan

t

P Improves Alfalfa Growth and Recovery

Li et al., 1998

Alfalfa regrows faster aftercutting with adequate P

0

20

40

60

80

100

120

0 7 14 21 28

Days after cutting

Sh

oo

t w

eig

ht,

mg

/pla

nt

P conc., mmol

0126

Alfalfa develops more shoots after cutting with adequate P

0

1

2

3

4

5

0 7 14 21 28

Days after cutting

Sh

oo

ts/p

lan

t

P conc., mmol

0126

P Response: Timing and Application Study

• Six-year study initiated to evaluate effect of P timing and application method

• Broadcast or banded P fertilizer

• Frequency: – 100 lb P2O5/A every year

– 200 lb P2O5/A every 2 years

– 600 lb P2O5/A in a one-time preplant application

• Total 6-year P rate was the same for all treatments: variables were timing and placement

Mullen et al., 2000; OK

Yield Response to P inYears One and Six

Knifed-in 6 in. deepP application, lb P2O5/A and frequency

0

10

20

30

100/yr 200/2 yr 600/6 yr 200/2 yr 600/6 yr

Year 1 Year 6

Alf

alf

a y

ield

res

po

nse

, %

in

crea

se

abo

ve c

hec

k

Mullen et al., 2000; OK

Yield Response:Method and Timing

P Application, lb P2O5/A and frequency

Knifed-in 6 in. deep

Cumulative Yield Response

3.4

4.24.7

5.8

6.8

0

1

2

3

4

5

6

7

100 lbs/A/yr 200 lbs/A/2-yr 600 lbs/A/6-yr 200 lbs/A/2-yr 600 lbs/A/6-yr

To

tal y

ield

incr

ease

, to

n/A

Mullen et al., 2000; OK

Increase in Alfalfa GrowthDue to P Fertilization(split over 5 years or one-time application)

Broadcast application

Ave

rag

e an

nu

alyi

eld

in

crea

se,

lb/A

P application, lb P2O5/A

0

1000

2000

3000

4000

5000

6000

100 200 300 400

5-yr splitapplication

One-timeapplication

Mullen et al., 2000; OK

Increase in Alfalfa GrowthDue to P Fertilization(split over 5 years or one-time application)

P application, lb P2O5/A

0

1000

2000

3000

4000

5000

6000

100 200 300 400

5-yr split Papplication

One-time Papplication

Disc-band application

Ave

rag

e an

nu

alyi

eld

in

crea

se,

lb/A

Mullen et al., 2000; Alberta

Influence of P Application on Increasing Alfalfa Yield (one-time application or annual application)

0

1000

2000

3000

4000

5000

6000

Yea

r 1

Yea

r 2

Yea

r 3

Yea

r 4

Yea

r 5

5-yr

Avg

Annual Papplication

One-time Papplication

Broadcast application

Ave

rag

e an

nu

alyi

eld

in

crea

se,

lb/A

Mullen et al., 2000; Alberta

Influence of P Application on Increasing Alfalfa Yield (one-time application or annual application)

0

1000

2000

3000

4000

5000

6000

7000

Year 1

Year 2

Year 3

Year 4

Year 5

5-y

r A

vg

Annual Papplication

One-time Papplication

Disc-band application

Ave

rag

e an

nu

alyi

eld

in

crea

se,

lb/A

Mullen et al., 2000; Alberta

James, 1995; Utah

• Yield response to added P most evident at first cutting

• Soil P fertility was maintained by small annual applications or a large one-time application

Alfalfa Response toAdded P Fertilizer

P application rate, lb P2O5/A

0 225 450

Cut 3

Cut 2

Cut 1

(STP=8 ppm, 0-45-0)

To

tal 3

-yea

r yi

eld

, to

n

Established StandsOften Need Additional P

• Soil testing and tissueanalysis can revealneed for fertilization.

• P fertilizer does not movefar in soil:

– Soil incorporationprior to planting is best

– Top-dressed and irrigated P is suitablefor subsequent fertilization

• P moves during freeze/thaw cycles, washes into soil cracks, and is taken up by shallow surface roots and crowns and becomes available for plant uptake.

Ottman et al., 2001; AZ

What P Source Is Superiorfor Alfalfa?

• Three-year study with 24 cuttings:– 10-34-0 applied in irrigation water

– 10-34-0 sprayed on soil surface

– 11-52-0 granules broadcast applied • (0, 20,40, 60, 100 lb P2O5/A/yr for 3 years)

• Positive hay yield response to P, but:– No differences in P sources or methods

of application in yield or tissueP concentration

Koenig, 2003; Utah

P Source? Not a Significant Factor for Alfalfa Yields

• Four P sources compared(2 liquid, 2 solid):

– Yield response to P fertilization(11 to 27% increase) under irrigation

No differences in P fertilizersources

• Placement compared:– Surface banding or broadcast on

established alfalfa stands

No yield differences due tofertilizer placement

Cihacek, 1993; NM

0

2

4

6

8

10

12

14

Check MAP DAP APP

Treatment

So

il T

est

P,

pp

m

Initial198219831984

(annual application, 115 lb P2O5/acre)

7 ppm critical value

Effect of P Fertilizeron Soil P Concentrations

• Failure to replace harvested nutrients will gradually deplete soil nutrient supply and reduce yields

Prior to planting:

• Incorporate P forestablishment of strongroot systems, promotingrapid recovery, andmaintaining healthy stands

• Provide balanced nutrition:Adequate K, Ca, Mg, S, B, etc.

• Eliminate soil pH problems - alfalfa does not thrive in acid soils

Low P

AdequateP

Preparing the Soil Before Planting Is Key

0

3

6

9

Year 1 Year 2 Year 3

No P or K

K only

P only

P and K

Alf

alfa

hay

yie

ld, t

on

/A/y

r

Berg et al., 2005; IN

Balanced P and K NutritionIs Essential for OptimalYields and Stand Maintenance

Proper Attention to All Nutrients Is Required for Healthy Plants and High Yield Levels

Berg et al., 2005; IN

General Guidelines for P Fertilization

• Use soil testing to guide P fertilization decisions and use local recommendations for best results

• Incorporate adequate P into the top 2 to 6 in. of soil prior to planting to meet the first years of productionand nutrient removal in harvested hay

• Use tissue analysis to determine need for subsequent-year phosphate

• Application can be made any time of the year-- frequently during winter months to meet the high-demand period in the Spring

– (avoiding application to snow-covered, frozen, or saturated fields with the potential risk of runoff)

Diagnosis of P Deficiencies

• Visual Observation:– Distinct P deficiencies are seldom observable

on alfalfa – not an effective diagnostic method!

• Soil Testing– Soil test prior to planting and regularly afterwards

• Tissue Analysis– Best way to monitor plant performance and

prevent hidden hunger and yield loss

• Recommended tissue concentration:– 0.25 to 0.40% P in top third of plant

Both P Fertilizer and Animal Manure Provide Nutrition for Alfalfa

Goss & Stewart, 1979; Texas

Cu

mu

lati

ve a

lfal

fa y

ield

, g/p

ot

Manure Management

• Manure supplies many nutrients –but not in the ratio required for crops

• Physical problems –compaction, crown damage,leaf burn, salinity

• Nutritional problems –N can stimulate weeds, extra Kcan cause cation imbalance for dairy feed rations

• Excessive manure applicationmay buildup P concentrations to levelsof concern in water runoff

Summary-P Nutrition of Alfalfa

• Alfalfa roots grow best in nutrient-rich soil; Prepare the seedbed prior to planting and supplement in later years as needed

• Adequate P promotes vigorous N2 fixation, shoot development, and faster regrowth after cutting

• Uptake of P continues through the season and is harvested in large amounts. The P fertilizer source is not important

• Placement near the seedling boosts establishment and stand longevity

• Crop response to P is best predicted with a soil test and subsequent tissue testing

• Nutrient management is an essential key to profitability and efficient use of other inputs

International Plant Nutrition Institute (IPNI)655 Engineering Drive, Suite 110Norcross, GA 30092-2837Phone: 770-447-0335; Fax 770-448-0439Website: www.ipni.net

Reference 06128