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Potassium Nutrition of Alfalfa. Potassium (K) Nutrition of Alfalfa. Outline: Plant development Diagnosis Yield and quality Economics Irrigation and record yields Cation competition Balanced nutrition. Alfalfa Production. In addition, Canada has 11 million acres yielding 1.4 ton/A

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potassium k nutrition of alfalfa
Potassium (K) Nutritionof Alfalfa


  • Plant development
  • Diagnosis
  • Yield and quality
  • Economics
  • Irrigation and record yields
  • Cation competition
  • Balanced nutrition
alfalfa production
Alfalfa Production
  • 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
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



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)

alfalfa root morphology approximately 3 months after planting



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

Weaver, 1926 (NE)

alfalfa root morphology end of first year



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

Weaver, 1926 (NE)

alfalfa root morphology july 10 second year



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

Weaver, 1926 (NE)

factors restricting root growth reduce nutrient uptake
Factors Restricting Root Growth Reduce NutrientUptake

Disease damage

Nutrient deficiencies

Excess salt or sodium

Poor nodulation

Soil compaction

Poor drainage

Insect damage

Low oxygen



recovery of k from various soil depths
Recovery of K fromVarious Soil Depths

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
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
K Deficiency in Alfalfa

Severe K Deficiency

Moderate K Deficiency

typical k concentrations at optimum fertility
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

Lanyon and Smith, 1985

k concentration declines with maturity

Shoot K, %

Growth Stage

K Concentration Declineswith Maturity

Barton and Reid, 1977 (WV)

soil testing and plant analysis
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
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)

k fertilization increases nodule activity

K2O added, lb/A

K Fertilization IncreasesNodule Activity

Grewal and Williams, 2002 (Australia)

k fertilization improves hay quality

K2O added, lb/A

K Fertilization ImprovesHay Quality

Grewal and Williams, 2002 (Australia)

k helps reduce winterkill in alfalfa

No K

100 lb K





Stand density (%)













K Helps Reduce Winterkillin Alfalfa

Plant counts taken in May as % of those previous September

Bailey, 1983 (MB)

alfalfa responses to k in mixed stands
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
response to k increases over life of stand
Response to K IncreasesOver Life of Stand

4-yr total

Most Economic Rate

Hay yield, tons/A





Initial soil test Kwas 35 ppm (low)

Fertilizer K2O, lb/A

Klausner and Goyette, 1993 (NY)

response to k increases over life of stand23
Response to K IncreasesOver Life of Stand

Rock Springs


Yield, tons/A

Most Economic Rate

Alfalfa response to K at two sites

Forage K, %

Initial soil test K ranged

from 130 to 170 ppm

Fertilizer K2O, lb/A

Beegle, 1992 (PA)

response to k increases over life of stand24



occurred in

5th year

Added K, lb K2O/A

Response to K IncreasesOver Life of Stand

Berg et al., 2003 (IN)

response increases after intensive management
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

Most Economic Rate

Yield, tons/A



Forage K, %


Fertilizer K2O, lb/A

Sheard et al., 1988 (ON)

soil k levels turn k fertilization into profit
Soil K Levels:Turn K Fertilizationinto Profit

Example: 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)

economics of k fertilization
Economics ofK Fertilization

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

profitability short vs long term
Profitability:Short vs. Long-Term

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

k fertilization according to soil test recommendation maintains alfalfa stands

Recommended K rate

Alfalfa stand density, plants/ft2

K2O application rate, lb/A

K Fertilization According toSoil Test RecommendationMaintains Alfalfa Stands

Burmester et al., 1991 (AL)

alfalfa response to soil ph



Yield, tons/A









Soil pH

Alfalfa Response to Soil pH

Follet and Wilkinson, 1995

liming acid soil improves alfalfa growth and nutrient recovery

pH 6.1

pH 5.3


pH 4.7

Yr 3

Alfalfa yield, ton/A

Yr 3

Yr 2

Yr 2

Yr 2

Yr 1

Yr 1

Yr 1

Liming Acid Soil Improves Alfalfa Growth andNutrient Recovery

Walworth and Sumner, 1990 (GA)

liming acid soil improves alfalfa growth and nutrient recovery32

Alfalfa shoot composition

Liming Acid Soil Improves Alfalfa Growth and NutrientRecovery

Walworth and Sumner, 1990 (GA)

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
optimum k rate in irrigated alfalfa an example

Cumulative Hay Yield, Tons






K2O rate, lb/A

Optimum K Rate in Irrigated Alfalfa: An Example

Best economic return

Too much in

one application

Koenig, 2002 (UT)

placement and application options
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
k impacts fall harvest more than spring

Spring Harvest, 2001

Fall Harvest, 2000

K applied, lb K2O/A

K applied, lb K2O/A)

K Impacts Fall Harvestmore than Spring
  • 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)

manure management
Manure Management
  • Manure supplies many nutrients
    • but usually not in the ratio requiredfor 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 for dairy feed
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 efficientlyrecycle 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
k competes with other cations for plant uptake mg

Tissue Mg, %

Magnesium Concentrations in Alfalfa

K applied, lb K2O/A

K Competes with Other Cations for Plant Uptake: Mg

Burmester et al., 1991 (AL)

k competes with other cations for plant uptake ca

Calcium Concentrations in Alfalfa

Tissue Ca, %

K applied, lb K2O/A

K Competes with Other Cations for Plant Uptake: Ca

Burmester et al., 1991 (AL)

k fertilization reduces uptake of other soil cations na

Sodium, ppm

Sodium Concentrations in Alfalfa

K applied, lb K2O/A

K Fertilization ReducesUptake of Other SoilCations: NA

James, 1988 (UT)

fertilization according to soil test recommendations

Recommended K rate

Yield, tons/A

K applied, lb K2O/A

Fertilization According to Soil Test Recommendations

Burmester et al., 1991 (AL)

summary k nutrition of alfalfa
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

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