Potassium Nutritionof Alfalfa

Potassium (K) Nutritionof Alfalfa

Outline:1. Plant development

2. Diagnosis

3. Yield and quality

4. Economics

5. Irrigation and record yields

6. Cation competition

7. Balanced nutrition

Alfalfa Production

U.S. Alfalfa Production and Yield

0

5

10

15

20

25

30

1920 1940 1960 1980 2000

Mill

ion

acre

s

0

1

2

3

4

5

6

Yie

ld (

ton

/A)Production

Yield

• In addition, Canada has 11 million acres yielding 1.4 ton/A• U.S. crop value $7 billion per year, 2000-2003

USDA-NASS; Statistics Canada

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

• Nutrient applications increase root growth, enabling roots to obtain moisture and nutrients from greater volume of soil

Alfalfa Root Morphology(Approximately 2 Months after Planting)

• Dryland– Deeper penetration

– Fewer but longer laterals

– More secondary branches

• Irrigated– Shallower

– More but shorter laterals

– Less secondary branches

Weaver, 1926 (NE)

Dryland Irrigated

Alfalfa Root Morphology(Approximately 3 Months after Planting)

• Dryland– Root system is more

profusely branched

– Branches reached same depth as tap root

– Shallower root system

• Irrigated– Fewer branches

– Greater rooting depth

– Tap root is the dominant structure Dryland Irrigated

Weaver, 1926 (NE)

Alfalfa Root MorphologyEnd of First year

• Dryland– Greater number of branches in

upper 1 ft. of soil

– Maximum depth of 5 ft.

– Roots oriented downward

• Irrigated– Fewer branches in upper 1 ft. of

soil

– Maximum depth of over 6 ft.

– Greater lateral extent of root system

Dryland Irrigated

Weaver, 1926 (NE)

Alfalfa Root MorphologyJuly 10, Second Year

• Dryland– Depth of over 9 ft.

– Roots oriented downward

– Little lateral extension

• Irrigated– Depth of nearly 10 ft.

– Greater lateral extention

IrrigatedWeaver, 1926 (NE)

Dryland

Factors Restricting Root Growth Reduce NutrientUptake

Disease damage

Insect damage

Temperature Acidity

Low oxygen

Poor drainage

Excess salt or sodium

Nutrient deficiencies

Poor nodulation

Soil compaction

Recovery of K fromVarious Soil Depths

Depth of placement, in. Recovery, % of applied

Surface 41

0-6 29

6-12 19

12-18 16

18-24 10

30-36 11

Recovery at the end of the growing season with K placed in the Spring at various depths in an established alfalfa stand

Peterson and Smith, 1973

Diagnosis of Nutrient Deficiencies

• Visual Observation

• Soil Testing

• Tissue Analysis

In K-deficient alfalfa, small white or yellowish spotsfirst appear around theouter edges of older leaves

K Deficiency in Alfalfa

Moderate K Deficiency Severe K Deficiency

Typical K Concentrations(at optimum fertility)

• Stems near top of plant contain themost K

• Leaf K concentration is similar among upper and lower leaves

• Roots contain less K

• Forage containing 2.5% K removes 60 lb of K2O per ton of dry matter harvested

Plant part andgrowth stage

K, % on dry matter basis

Stems: near ground level

2%

Stems: near top up to 6%

Leaves: 1.8 - 2.2%

Roots: 1.1%

Forage harvested at early bloom:

1.8% to 2.5%

Top 6 in. at bud to early bloom:

2.0% to 3.5%

Lanyon and Smith, 1985

K Concentration Declineswith Maturity

Barton and Reid, 1977 (WV)

0

1

2

3

Vegetative Bud EarlyBloom

FullBloom

Seed

Growth Stage

Sh

oo

t K

, %

Soil Testing andPlant Analysis

• Soil Testing– Verify that K levels are being maintained

– Soil pH 6.5 or higher for efficient N fixation

• Plant Analysis– Usually sample the top 6 in. at harvest

– Indication of adequate K fertility:• <2% indicates insufficient K for winter hardiness

• Optimum yields usually contain around 2.5% K

• Record yield of 10 tons/A (non-irrigated), K content of 3%

K Deficiency Hurts More Than Yield

Adequate K Improves:– Plant persistence

– Number of shoots per plant

– Shoot yield

Deficient K:– Reduces root starch storage

– Reduces protein concentration in root

– Results in poor survival and slowshoot growth

Li et al., 1997 (IN)

0

10

20

30

40

50

60

70

Nodule number Nodule weight, mg

0 21 43 64 86 107K2O added, lb/A

Grewal and Williams, 2002 (Australia)

K Fertilization IncreasesNodule Activity

0

20

40

60

80

100

Leaf Drop (%) Leaf SpotRating

Leaf/Stem Ratio(x100)

0 21 43 64 86 107K2O added, lb/A

K Fertilization ImprovesHay Quality

Grewal and Williams, 2002 (Australia)

Plant counts taken in May as % of those previous September

Bailey, 1983 (MB)

K Helps Reduce Winterkillin Alfalfa

100

1971 1972 1973 1974 1975 1976 19770

20

40

60

80

Sta

nd

de

ns

ity

(%

)

100 lb K2O/yrNo K

Year

Alfalfa Responses to Kin Mixed Stands

• Largest where soil K fertilitylevels are low

• Increases over the lifeof the stand

• Includes quality as wellas yield

– Increased proportion oflegume to grass more protein

• Increases in irrigated production

Ha

y y

ield

, to

ns

/A

Fertilizer K2O, lb/AInitial soil test K

was 35 ppm (low)

4-yr total

19891992

1990

1991

Most Economic Rate

Klausner and Goyette, 1993 (NY)

Response to K IncreasesOver Life of Stand

Rock Springs Landisville

Yie

ld,

ton

s/A

Fo

rag

e K

, %

Fertilizer K2O, lb/A

Alfalfa response to K at two sites

Most Economic Rate

Beegle, 1992 (PA)

Initial soil test K rangedfrom 130 to 170 ppm

Response to K IncreasesOver Life of Stand

Berg et al., 2003 (IN)

0

5

10

15

20

25

30

35

0 100 200 300 400

Cum

ula

tive

yie

ld, ton/A

1998 1999 2000 2001 2002

Added K, lb K2O/A

Greatestresponseoccurred in5th year

Response to K IncreasesOver Life of Stand

Yie

ld, t

on

s/A

Fertilizer K2O, lb/A

Fo

rag

e K

, %

Most Economic Rate

1985

1986

Sheard et al., 1988 (ON)

1985

1986

Response increases after intensive management

• Alfalfa response to K under intensive 5-cut management

• Initial soil test K of 170 ppm in 1984, declined to 80 ppm in the unfertilized treatment by spring 1987

Soil K Levels:Turn K Fertilizationinto ProfitExample: Annual economic returnto K fertilizer use:Assuming $90 per ton of hay and K2O at $0.15 per pound (price ratio of 3 lb hayper lb of K2O)

Soil test Kcategory

Yieldresponse

K2O rate Net return

tons/A lb/A $/A

Very low 1.2 335 57.75

Low 1.0 260 51.00

High 0.2 90 4.50

Economics ofK Fertilization

The most economic rate of K fertilization changes as the ratio of K prices to hay prices changes

Soil Test KPrice Ratio

Category 2 3 4 5

Most economic rate of K2O (lb/A)

Very low 425 335 270 220

Low 330 260 214 175

High 130 90 60 40

Profitability:Short vs. Long-Term

The yield increase in response to K application gets larger as the alfalfa stand ages

Alfalfa Yield Response to Annually Applied K

0.0

0.5

1.0

1.5

2.0

2.5

1 2 3 4 5 6 7

Age of stand, years

Yiel

d re

spon

se, t

ons/

A

Quebec

Pennsylvania

New York

Manitoba

Missouri

Burmester et al., 1991 (AL)

0

4

8

12

16

120 240 440 550 640

K2O application rate, lb/A

Alf

alf

a s

tan

d d

ens

ity,

pla

nts

/ft2

K Fertilization According toSoil Test RecommendationMaintains Alfalfa Stands

Recommended K rate

Follet and Wilkinson, 1995

0

1

2

3

4.5 5 5.5 6 6.5 7

Soil pH

Yie

ld, t

on

s/A

Alfalfa Response to Soil pH

Walworth and Sumner, 1990 (GA)

Liming Acid Soil Improves Alfalfa Growth andNutrient Recovery

0

2

4

6

8

0 2100 3400

Lime added, lb/A

Yr 1Yr 1Yr 1

Yr 2

Yr 2Yr 2

Yr 3

Yr 3

Yr 3pH 5.3

pH 6.1

pH 4.7

Alfa

lfa y

ield

, to

n/A

Liming Acid Soil Improves Alfalfa Growth and NutrientRecovery

Walworth and Sumner, 1990 (GA)

0

1

2

3

N K Ca

pH 4.7

pH 5.3

pH 6.1

Alfa

lfa s

hoot

com

posi

tion

How Does this Changewith Irrigation?

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

0

2

4

6

8

10

12

14

16

Cum

ulat

ive

Hay

Yie

ld,

Ton

s

K2O rate, lb/A

0 200 400 600 600

Optimum K Rate in Irrigated Alfalfa: An Example

Koenig, 2002 (UT)

Bes

t ec

onom

ic r

etu r

n

To

o m

uch

in

on

e ap

plic

atio

n

Placement and Application Options

• Establishment– Broadcast to build up soil test K before seeding

– Banded starters should contain mostly P

• Maintenance– Apply following harvest to replace removal

– High rates: split over several cuts to avoid salt injury

– To boost winter hardiness, apply before critical fall growth period (before last 6 weeks of growth)

– When soil K levels are high, spring applications can lead to higher K levels than desired, and may be unnecessary

• Yield response to K found in last harvest of 2000 • For first harvest of 2001, no response to K fertilization was observed

Reason:K can be released from soil minerals during winter and spring

Volenec, 2002 (IN)

K Impacts Fall Harvestmore than Spring

0

0.3

0.6

0.9

1.2

0 100 200 300 400

Hay

yie

ld, t

ons/

A

Fall Harvest, 2000

K applied, lb K2O/A)

0

0.3

0.6

0.9

1.2

1.5

1.8

0 100 200 300 400

Hay

yie

ld, t

ons/

A

Spring Harvest, 2001

K applied, lb K2O/A

Manure Management

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

for alfalfa!

• Physical problems– compaction, crown damage,

leaf burn, salinity

• Nutritional problems– N can stimulate weeds

– excessive K can cause cation

– imbalance in dairy feed rations

Luxury Uptake of K forDairy Feed

• K in alfalfa varies from<1.5% to >3%

– Luxury uptake when soil Kis very high

– K levels above 3% unnecessary– Liquid manure systems efficiently

recycle K

• High K forage: A concern fordry dairy cows

– Leads to milk fever, retained placentas after calving– For the transition period (2 to 4 weeks before calving) forage

with <2% K desired; dietary K should be <1.2%– Corn silage, grains, distillers grains are low K feeds

– Anionic salts (chlorides or sulfates of NH4+, Mg, or Ca) can help

correct the problem

Burmester et al., 1991 (AL)

0

0.1

0.2

0.3

0 150 300 450 600

K applied, lb K2O/A

Tis

sue

Mg

, %

Magnesium Concentrations in Alfalfa

K Competes with Other Cations for Plant Uptake: Mg

0

0.4

0.8

1.2

1.6

0 150 300 450 600

K applied, lb K2O/A

Tis

sue

Ca,

%

Calcium Concentrations in Alfalfa

K Competes with Other Cations for Plant Uptake: Ca

Burmester et al., 1991 (AL)

K Fertilization ReducesUptake of Other SoilCations: NA

0

500

1000

1500

2000

2500

3000

0 100 200 300 400

James, 1988 (UT)

Sodium Concentrations in Alfalfa

K applied, lb K2O/A

Sod

ium

, pp

m

0

1

2

3

4

5

6

7

8

1998 1999 2000 2001 2002

No P or K

P only

P and K

Alf

alf

a h

ay y

ield

, to

n/A

/yr

Berg et al., 2003 (IN)

Balanced P and K Nutrition Is Essential for Optimal Yieldsand Stand Maintenance

Recommended K rate

0

2

4

6

8

10

12

14

16

120 240 340 440 540 640

Yr 3

Yr 2

Yr 1

Yie

ld,

tons

/A

K applied, lb K2O/A

Fertilization According to Soil Test Recommendations

Burmester et al., 1991 (AL)

Summary – K Nutrition of Alfalfa

• Alfalfa takes up and removeslarge amounts of K from the soil

• Fertilization is essential for highyields, stand longevity,and winter hardiness

• Fertilized to optimum, foragecontains 2 to 3% K

• Application: pre-plant and following harvests

• Apply recommended rates to avoid luxury uptake

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