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Phosphorus Nutrition of Alfalfa. Phosphorus (P) Nutrition of 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 - PowerPoint PPT Presentation
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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