Phosphorus Nutrition of Soybean

1
Phosphorus Nutrition of Soybean
2
Outline P Nutrition of Soybean

• P uptake by above-ground plant tissue
• Soybean root morphology
• P influx by roots
• Yields and soil test P levels
• P placement
• P timing
• P and soybean pests/diseases

3
P Uptake by Above-Ground Plant Tissue

• Examining uptake throughout the season

4
Nutrient Uptake by 80 bu/A Soybeans
Source Henderson and Kamprath, 1970
5
Soybean P Uptake
100
90
80
Total P uptake12 24 lb P2O5/A
Beans
70
60
Pods
50
of total uptake
Petioles
Stems
40
30
20
Petioles (fallen)
Leaves
10
Leaves(fallen)
0
Days after emergence
0
28
56
84
112
V1
V6
V10
R4
R6
R7
Growth stage (inferred)
Source Hanway and Weber, 1971
6
Soybean Phosphorus Derivedfrom Fertilizer
Source Ham and Caldwell, 1978
7
Soybean Phosphorus Content Derived from Fertilizer
Soil P level
60
Low
50
40
Medium
30
of P derived from fertilizer
High
20
10
0
20
40
60
80
100
120
Days after planting
Source Bureau et al., 1953
8
Soybean Root Morphology

• Establishing a background for discussions of P
  placement

9
Soybean Root Growth
6 in.

• Phase 1(1st month after planting)
• Rapid vegetative top growth
• Downward taproot growth
• Development of horizontal laterals in upper soil
  profile

Source Mitchell and Russell, 1971
10
Soybean Root Growth

• Phase 2(2 2.5 months after planting)
• High rates of top growth(from flowering through
  pod formation)
• More laterals develop in upper soil profile
• Some laterals begin to turn downward

6 in.
Source Mitchell and Russell, 1971 Raper and
Barber, 1970
11
Soybean Root Morphology

• Left sidesingle soybean plant grown in isolated
  plot
• Primary lateral roots branch from taproot within
  upper 15 cm (6 in.)
• Below 15 cm (depth of cultivation), taproot
  degenerated to a root with a diameter similar to
  primary laterals but with less branching

(approx. 10 wk. after planting)
Source Raper and Barber, 1970
12
Soybean Root Morphology

• Right sidesoybean grown in 30 in. rows
• Primary lateral roots branch from taproot within
  upper 15 cm (6 in.)
• Near center of rows (45 cm or 18 in.), laterals
  angle down sharply as they encounter root zone of
  neighboring plant

(approx. 10 wk. after planting)
Source Raper and Barber, 1970
13
Soybean Root Growth

• Phase 3(Seed set to maturity)
• Continued rapid rates of downward extension of
  laterals
• Laterals penetrated deeper than the tap root

Source Mitchell and Russell, 1971
14
Roots Proliferate in Zones of Higher P
Concentration
0.8
Soybean
0.7
Corn
0.6
11
0.5
Portion of total root lengthin P-treated volume
0.4
0.3
0.2
0.1
0
0
0.1
0.2
0.3
0.4
0.5
0.6
P treated soil portion,
Source Borkert and Barber, 1985
15
Effects of P or Mycorrhizae on Soybean Shoot
Dry Weight
Greenhouse study
Non- mycorrhizal DM
Mycorrhizal DM
3.0
100
Non-mycorrhizal infection
Mycorrhizal infection
2.5
80
2.0
60
Shoot dry weight, grams
of root colonized
1.5
40
1.0
20
0.5
Initial Bray 1 soil test P 8 ppm
0
0
0
115
345
920
Applied P rate, lb P2O5/A
Source Lambert et al. 1979
16
Management Factors Affecting Soybean Root
Morphology

• Cultivar choice
• Root angle
• Root elongation rate
• Planting date
• Soil temperature
• Soil moisture
• Photoperiod
• Quantity of radiation

• Tillage
• Soil moisture
• Soil temperature
• Soil bulk density
• Soil aeration
• Soil fertility
• Plant dry matter distribution
• Root proliferation
• Irrigation
• Soil moisture profile

Source Coale and Grove, 1986
17
P Influx by Roots

• Examining how quickly roots can absorb P

18
Nutrient Influx by Roots

• Ions are not simply absorbed according to their
  ratios in solution
• Ions with this characteristic influx pattern
  require energy to be absorbed
• H2PO4-, HPO42-
• K
• Maximum influx is reached at higher solution
  concentrations (Imax)

22-23 day old soybean roots
3.0
Imax
2.5
2.0
1.5
Influx, 10-14 lb P2O5 / (in2 s)
1.0
0.5
0.0
0
1
2
3
4
5
-0.5
Solution P, 10-6 lb P2O5/gal
Sources Barber, 1984 Edwards and Barber, 1976
19
Nutrient Influx Depends on Both P and K Fertility
Low P limits P diffusionand energy for P uptake
Low P limits energyfor K uptake
P2O5 influx by soybean roots
K2O influx by soybean roots
10.0
55 ppm Bray P-1
9.0
8.0
7.0
55 ppm Bray P-1
6.0
Influx, 10-13 lb / (in2 s)
5.0
4.0
3.0
11 ppm Bray P-1
11 ppm Bray P-1
2.0
1.0
0.0
50
70
90
110
130
150
50
70
90
110
130
150
Soil test K, ppm
Source Hallmark and Barber, 1984
20
P Influx Varies withPlant Age
5
4
3
Influx, 10-5 lb P2O5 / (in. day)
2
1
Soybean
0
0
20
40
60
80
100
120
-1
Plant age, days
Sources Barber, 1978 Mengel and Barber, 1974
21
Yields and Soil Test P Levels

• Examining how productionlevel is related to soil
  testP level

22
Soil Test P Calibration Data
Source Mallarino, 1999
23
Comparisons of Soil Test P Calibration Data
120
100
80
60
Relative yield,
40
20
0
0
5
10
15
20
25
30
35
40
0
5
10
15
20
25
30
35
40
Bray P-1 soil test level, ppm
Source Snyder, 2000
24
P placement

• Broadcast and bandedapplications

25
Nutrient Placement Considerations
Conceptual model(nutrient deficient soil)

• Banding
• Less soil volume fertilized
• Smaller portion of fertilizer is tied up
• Roots proliferate where N and P are found
• Rate may be too low to maximize yield
• Fewer roots exposed to supply
• Increase in influx rate by roots may not
  compensate for fewer total number of roots near P
  supplies

High nutrient rate
Dry matter yield
Low nutrient rate
0
100
20
40
60
80
Fertilized soil fraction,
Source Anghinoni and Barber, 1980
26
Starter vs. BroadcastIrrigated Zone

• 3 of 10site-years responded significantly
• pH 7.6 8.1
• Olsen P 5.6 10.7 ppm
• Calcareous soil
• Band placement2 in. below2 In. to the side
  (2x2)

Range in average yields50 - 71 bu/A
25
20
Broadcast
15
2x2 Band
10
Soybean yield response,
5
0
0
20
40
60
80
100
-5
P2O5 rate, lb/A
Source Rehm, 1986
27
Starter vs. BroadcastDryland Zone
60
50
1 in. below
40
1 in. x 1 in.
30
Yield response,
With seed
20
Spring broadcast
10
Fall broadcast
0
0
25
50
75
100
125
-10
P rate, lb P2O5/A
Source Bullen et al., 1983
28
Starter vs. broadcastTemperate Rain Fed Zone

• 20 site-years at research stations
• 4 29 ppmBray P-1
• 9 sites tested Very Low to Low(6 to 15 ppm Bray
  P-1)
• 7 of the 9 sites (78)(6 to 11 ppm Bray P-1)
  showed significant responses to P
• P placement did not influence soybean yield

Averaged overresponsive sites
13.1
14
11.6
12
Averaged overall sites
10
8
Yield response,
6
3.9
3.9
4
2
0
Starter
Starter
Broadcast
Broadcast
Source Borges and Mallarino, 2000
29
Comparison of Placement Combinations and Rates
19.9
19.6
20
Bray P-1 3.5 ppmNH4OAc K 150 ppm
14.0
15
Yield response,
10
7.2
broadcast w/seed
5.0
broadcast band
5
broadcast
w/seed
band
0
N
4
10
0
4
10
P2O5
18
46
60
78
106
K2O
5
12
30
35
42
Source Ham et al., 1973
30
Deep Banding vs. Broadcast

• 20 site-years at research stations
• No-till systems
• 0 6 in. soil samples
• 4 29 ppm Bray P1
• pH 5.9 7.1
• Significant responses to P occurred on 7 sites
  ranging from 6 11 ppm Bray P1
• Average response at these sites4.6 bu/A
• 5 of the 7 sites showed no differences in
  placement

Range in average yields26 63 bu/A
30 in.
6 - 8 in.
30 in.
Source Borges and Mallarino, 2000
31
Deep Banding vs. Broadcast

• 11 site-years on farmer fields
• No-till systems
• 0 6 in. soil samples
• 5 34 ppm Bray P1
• pH 5.8 7.5
• Across all site-years, there was a slight(1
  bu/A) advantage to P fertilization, and no
  difference between placement methods

Range in average yields37 58 bu/A
7.5 in.
6 - 8 in.
30 in.
Source Borges and Mallarino, 2000
32
Considerations forPlacement

• Banding is expected to be superior when soil test
  levels are low and only smaller rates of P are
  applied
• Broadcast applications may be superior to banded
  applications when rainfall or irrigation keeps
  moisture in the upper part of the soil profile
• Placement of bands directly below the seed may be
  better than other band placements
• Band and broadcast applications used together may
  be better than either one applied on its own

33
P Timing

• Comparing fresh andresidual effects of
  fertilization

34
Annual vs. BiennialBroadcast Applications
Range in average yields24 48 bu/A

• Corn/soybean rotation
• Long no-till history
• P timing (0-46-0)
• Every 2-yr.80 lb P2O5/A
• Every yr.40 lb P2O5/A
• 2 of 4 site-years showedno timing differences
• 1 site (18 ppm Bray P1)annual gt biennial by 3
  bu/A
• 1 site (37 ppm Bray P1) biennial gt annual by 3
  bu/A

30 in.
Source Buah et al., 2000
35
Annual vs. BiennialBroadcast Applications

• Corn/soybean rotation
• Long no-till history
• P timing
• Every 2 yr.(0, 30, 80, 160 lb P2O5/A)
• Every yr. (0, 15, 40, 80 lb P2O5/A)
• Direct gt residual 2 out of 3 years
• 2 bu/A average response
• Bray P-1 6 14 ppm

Range in average yields37 46 bu/A
10 in.
Source Buah et al., 2000
36
Annual vs. BiennialStarter Applications

• Corn/soybean rotation
• Long no-till history
• P timing (0-46-0)
• Every 2-yr.80 lb P2O5/A
• Every yr.40 lb P2O5/A
• 2 of 4 site-years showedno timing differences
• 1 site (18 ppm Bray P1)annual gt biennialby 6
• 1 site (37 ppm Bray P1) biennial gt annual by13
  

Range in average yields24 48 bu/A
30 in.
3 - 4 in.
2 in.
30 in.
Source Buah et al., 2000
37
Annual vs. BiennialStarter Applications

• Corn/soybean rotation
• Long no-till history
• P timing
• Every 2 yr.(0, 30, 80, 160 lb P2O5/A)
• Every yr.(0, 15, 40, 80 lb P2O5/A)
• Annual gt biennial 2 out of 3 years
• 2 bu/A average response
• Bray P-1 6 14 ppm

Range in average yields37 46 bu/A
10 in.
4 in.
30 in.
Source Buah et al., 2000
38
Residual effect of a single, large application of
P
0 lb P2O5 applied initially67.5 lb P2O5/A
applied annually
120
110
100
90
of yield attained with 600 lb P2O5/A applied
initially, and 67.5 lb P2O5/A applied annually
80
600 lb P2O5 applied initially 0 lb P2O5/A
applied annually
70
60
50
40
1975
1980
1985
1990
1995
2000
Year
Source Dodd and Mallarino, 2005
39
Timing Considerations

• Cases where annual applications may be better
  than biennial applications in no-till systems
• Soils with lower soil test levels
• Soybeans planted in narrower rows
• Other tillage systems need to be investigated
• Single, larger applications of P can have
  significant residual value
• Builds soil test levels
• Can be performed when economics of larger
  applications are favorable
• Allows P to be omitted in times of unfavorable
  economic conditions

40
Phosphorus and soybean pests/diseases
41
Nutrition and Foliar DiseasesAsian Rust
Source Piccio and Fanje, 1980
42
Nutrition and DiseasesSoybean mosaic virus
50
K2O
45
40
35
30
P2O5
25
SMV incidence,
N
20
15
Total N P2O5 K2O,at equal rates
10
5
0
0
25
50
75
100
125
150
Nutrient rate, lb/A
Source Pacumbaba et al., 1997
43
Nutrition and NematodesSoybean cyst nematode
(SCN)
Cultivar highly susceptibleto SCN races 3 and 4
18
30
16
25
14
Yield response
12
20
10
Cysts / 100cc
15
Yield response,
8
6
10
4
5
2
0
0
0-0
30-30
60-60
90-90
120-120
Fertilizer mixture (P2O5 - K2O), lb/A
C/C
S/S
C/S
Yield response
Source Howard et al., 1998
44
Nutrition and NematodesSoybean cyst nematode
(SCN)
Cultivar resistantto SCN races 3 and 4
18
30
16
25
14
12
20
Yield response
10
Yield response,
Cysts / 100cc
15
8
6
10
4
5
2
0
0
0-0
30-30
60-60
90-90
120-120
Fertilizer mixture (P2O5 - K2O), lb/A
C/C
S/S
C/S
Yield response
Source Howard et al., 1998
45
Conclusions

• At harvest, most of the P in the above-ground
  portion of soybean is in the grain
• At lower soil test levels, more of the P taken up
  by the plant comes from applied P
• In the first month after planting, root
  development is primarily characterized by
  elongation of the taproot
• In subsequent months, soybean develops much of
  its root system near the soil surface
• Compared to corn, the rate of P influx by soybean
  roots is about 4 times slower in the first 20
  days
• P proliferates soybean roots when present in
  concentrated zones
• Mycorrhizae can increase soybean growth at low
  soil test P levels, even when P is applied

46
Conclusions

• Soil test calibration data provide a biological
  evaluation of chemical tests
• Average calibration relationships can be similar
  across large geographies
• Placement of bands directly below the seed may be
  better than other band placements
• Band and broadcast applications used together may
  be better than either one applied on its own
• Annual applications appear to be superior to
  biennial applications when plant spacing is
  narrower and soil tests are low
• P can help reduce the incidence and or severity
  of some soybean diseases

47

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