Phosphorus Nutrition of Soybean
Jan 03, 2016
Phosphorus Nutrition of Soybean
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
P Uptake by Above-Ground Plant Tissue
Examining uptake throughout the season
Nutrient Uptake by 80 bu/A Soybeans
0
50
100
150
200
250
300
350
400
450
0 20 40 60 80 100 120 140 160
Days after planting
Aer
ial
accu
mu
lati
on
(lb
/acr
e)
N P2O5 K2O
Source: Henderson and Kamprath, 1970
Soybean P Uptake
Days after emergence
Growth stage (inferred)
0 28 56 84 112
10
20
30
40
50
60
70
80
90
100
0
% o
f to
tal u
ptak
e
V1 V6 V10 R4 R6 R7
Beans
Pods
Stems Petioles
Petioles (fallen)Leaves
Leaves(fallen)
Total P uptake:12 – 24 lb P2O5/A
Total P uptake:12 – 24 lb P2O5/A
Source: Hanway and Weber, 1971
Soybean Phosphorus Derivedfrom Fertilizer
Soybean plant fraction P derived from fertilizer
(%)
Leaves (and petioles?) 36
Stems 20
Pods 25
Beans 16
Source: Ham and Caldwell, 1978
Soybean Phosphorus Content Derived from Fertilizer
0
10
20
30
40
50
60
20 40 60 80 100 120
Days after planting
% o
f P
de
riv
ed f
rom
fe
rtili
zer
Soil P level
Low
Medium
High
Source: Bureau et al., 1953
Soybean Root Morphology
Establishing a background for discussions of P placement
Soybean Root Growth
• Phase 1(1st month after planting)
– Rapid vegetative top growth
– Downward taproot growth
– Development of horizontal laterals in upper soil profile
6 in.
Source: Mitchell and Russell, 1971
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
Soybean Root Morphology
• Left side:single 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
Soybean Root Morphology
• Right side:soybean 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
Soybean Root Growth
• Phase 3(Seed set to maturity)
– Continued rapid rates of downward extension of laterals
– Laterals penetrated deeper than the tap root
Depth ofRoot dry weight at the following
days after planting:
sample 31 67 80 102
(in.) -------------- (grams) -------------
0 - 3 0.24 2.60 3.10 4.23
3 - 6 0.04 0.26 0.73 0.52
6 - 9 0.01 0.07 0.12 0.08
9 - 12 0.01 0.04 0.07 0.04
12 - 18 -- 0.05 0.10 0.04
18 - 24 -- 0.03 0.10 0.08
24 - 36 -- 0.07 0.08 0.07
36 - 48 -- -- 0.06 0.06
48 - 72 -- -- -- 0.03
Source: Mitchell and Russell, 1971
Roots Proliferate in Zones of Higher P Concentration
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0 0.1 0.2 0.3 0.4 0.5 0.6
P treated soil portion, %
Po
rtio
n o
f to
tal r
oo
t le
ng
thin
P-t
rea
ted
vo
lum
eSoybean
Corn
1:1
Source: Borkert and Barber, 1985
Effects of P or Mycorrhizae on Soybean Shoot Dry Weight
Source: Lambert et al. 1979
Greenhouse studyGreenhouse study
0
0.5
1.0
1.5
2.0
2.5
3.0
0 115 345 920
Applied P rate, lb P2O5/A
Sh
oo
t d
ry w
eig
ht,
gra
ms
0
20
40
60
80
100
% o
f ro
ot
colo
niz
ed
Non- mycorrhizal DM Mycorrhizal DMNon-mycorrhizal infection Mycorrhizal infection
Initial Bray 1 soil test P = 8 ppm
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
P Influx by Roots
Examining how quickly roots can absorb P
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-, HPO4
2-
– K+
• Maximum influx is reached at higher solution concentrations (Imax)
22-23 day old soybean roots22-23 day old soybean roots
-0.5
0.0
0.5
1.0
1.5
2.0
2.5
3.0
0 1 2 3 4 5
Solution P, 10-6 lb P2O5/gal
Infl
ux,
10-1
4 lb
P2O
5 /
(in
2 s)
Imax
Sources: Barber, 1984; Edwards and Barber, 1976
Nutrient Influx Depends on Both P and K Fertility
0.01.02.03.04.05.06.07.08.09.0
10.0
50 70 90 110 130 150
Soil test K, ppm
Infl
ux
, 10-1
3 lb
/ (
in2 s
)
50 70 90 110 130 150
P2O5 influx by soybean roots K2O influx by soybean roots
11 ppm Bray P-1
55 ppm Bray P-1
11 ppm Bray P-1
55 ppm Bray P-1
Low P limits P diffusionand energy for P uptakeLow P limits P diffusionand energy for P uptake
Low P limits energyfor K uptakeLow P limits energyfor K uptake
Source: Hallmark and Barber, 1984
P Influx Varies withPlant Age
-1
0
1
2
3
4
5
0 20 40 60 80 100 120
Plant age, days
Infl
ux,
10-5
lb
P2O
5 /
(in
. d
ay)
Corn
Soybean
Sources: Barber, 1978; Mengel and Barber, 1974
Yields and Soil Test P Levels
Examining how productionlevel is related to soil testP level
Soil Test P Calibration Data
100
80
60
40
20
00 10 20 30 40 50 60 70 80 0 10 20 30 40 50 60 70 80
Soil test Bray P-1, ppm
Rel
ativ
e g
rain
yie
ld,
%
Corn Soybean
Source: Mallarino, 1999
Comparisons of Soil Test P Calibration Data
0
20
40
60
80
100
120
0 5 10 15 20 25 30 35 40
Bray P-1 soil test level, ppm
Re
lati
ve
yie
ld, %
MO IL AR
0 5 10 15 20 25 30 35 40
KY MS AL
Source: Snyder, 2000
P placementBroadcast and bandedapplications
Nutrient Placement Considerations
• 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 Fertilized soil fraction, %
0 10020 40 60 80
Conceptual model(nutrient deficient soil)
Conceptual model(nutrient deficient soil)
Low nutrient rate
High nutrient rate
Dry
mat
ter
yiel
d
Source: Anghinoni and Barber, 1980
Starter vs. Broadcast:Irrigated Zone
• 3 of 10site-years responded significantly
• pH: 7.6 – 8.1
• Olsen P: 5.6 – 10.7 ppm
• Calcareous soil
• Band placement:2 in. below2 In. to the side (2x2)
-5
0
5
10
15
20
25
0 20 40 60 80 100
P2O5 rate, lb/A
So
ybe
an y
ield
re
spo
nse
, % Broadcast
2x2 Band
Range in average yields:50 - 71 bu/A
Range in average yields:50 - 71 bu/A
Source: Rehm, 1986
Starter vs. Broadcast:Dryland Zone
-10
0
10
20
30
40
50
60
0 25 50 75 100 125
P rate, lb P2O5/A
Yie
ld r
esp
on
se,
%
Source: Bullen et al., 1983
1 in. below
1 in. x 1 in.
With seed
Spring broadcast
Fall broadcast
Starter vs. broadcast:Temperate 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
3.9 3.9
13.111.6
02468
101214
Bro
adca
st
Sta
rter
Bro
adca
st
Sta
rter
Yie
ld r
esp
on
se,
%
Averaged overall sites
Averaged overresponsive sites
Source: Borges and Mallarino, 2000
Comparison of Placement Combinations and Rates
5.0
7.2
14.0
19.9 19.6
0
5
10
15
20
w/s
eed
band
broa
dcas
t
broa
dcas
t +
w/s
eed
broa
dcas
t +
ban
d
4 10 0 4 10
18 46 60 78 106
5 12 30 35 42Source: Ham et al., 1973
N:
P2O5:
K2O:
Yie
ld r
espo
nse,
%Bray P-1: 3.5 ppmNH4OAc K: 150 ppm
Bray P-1: 3.5 ppmNH4OAc K: 150 ppm
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 sites:4.6 bu/A
– 5 of the 7 sites showed no differences in placement
30 in.
30 in.
Range in average yields:26 – 63 bu/A
Range in average yields:26 – 63 bu/A
6 - 8 in.
Source: Borges and Mallarino, 2000
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
30 in.
7.5 in.
6 - 8 in.
Range in average yields:37 – 58 bu/A
Range in average yields:37 – 58 bu/A
Source: Borges and Mallarino, 2000
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
P TimingComparing fresh andresidual effects of fertilization
Annual vs. Biennial:Broadcast 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 > biennial by 3 bu/A
• 1 site (37 ppm Bray P1): biennial > annual by 3 bu/A
30 in.
Range in average yields:24 – 48 bu/A
Range in average yields:24 – 48 bu/A
Source: Buah et al., 2000
Annual vs. Biennial:Broadcast 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 > residual 2 out of 3 years
– 2 bu/A average response
– Bray P-1: 6 – 14 ppm
10 in.
Range in average yields:37 – 46 bu/A
Range in average yields:37 – 46 bu/A
Source: Buah et al., 2000
Annual vs. Biennial:Starter 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 > biennialby 6 %
• 1 site (37 ppm Bray P1): biennial > annual by13 %
30 in.
30 in.
Range in average yields:24 – 48 bu/A
Range in average yields:24 – 48 bu/A
2 in.
3 - 4 in.
Source: Buah et al., 2000
Annual vs. Biennial:Starter 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 > biennial 2 out of 3 years
– 2 bu/A average response
– Bray P-1: 6 – 14 ppm
10 in.
Range in average yields:37 – 46 bu/A
Range in average yields:37 – 46 bu/A
30 in.
4 in.
Source: Buah et al., 2000
Residual effect of a single, large application of P
40
50
60
70
80
90
100
110
120
1975 1980 1985 1990 1995 2000Year
% o
f yi
eld
att
ain
ed w
ith
600
lb
P2O
5/A
ap
pli
ed i
nit
iall
y, a
nd
67.
5 lb
P2O
5/A
ap
pli
ed a
nn
ual
ly
0 lb P2O5 applied initially67.5 lb P2O5/A applied annually
600 lb P2O5 applied initially 0 lb P2O5/A applied annually
Source: Dodd and Mallarino, 2005
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
Phosphorus and soybean pests/diseases
Nutrition and Foliar Diseases:Asian Rust
Rate Upper extent Lesion Type of Overall
N P2O5 K2O of rust lesions density pustule rating
(lb/A)
80 0 0 upper third heavy sporulating susceptible
0 61 0 upper third medium sporulating mod. susceptible
0 0 32 upper third medium sporulating mod. susceptible
80 184 0 upper third heavy sporulating susceptible
27 61 32 middle third medium non-sporulating mod. resistant
Source: Piccio and Fanje, 1980
Nutrition and Diseases:Soybean mosaic virus
K2O
P2O5
Total N + P2O5 + K2O,at equal rates
N
Source: Pacumbaba et al., 1997
05
101520
25303540
4550
0 25 50 75 100 125 150
Nutrient rate, lb/A
SM
V i
nci
den
ce,
%
Nutrition and Nematodes:Soybean cyst nematode (SCN)
02468
1012141618
0-0 30-30 60-60 90-90 120-120
Fertilizer mixture (P2O5 - K2O), lb/A
Cys
ts /
100c
c
0
5
10
15
20
25
30
Yield
respo
nse, %
C/C S/S C/S Yield response
Cultivar highly susceptibleto SCN races 3 and 4Cultivar highly susceptibleto SCN races 3 and 4
Source: Howard et al., 1998
Yield response
Nutrition and Nematodes:Soybean cyst nematode (SCN)
Source: Howard et al., 1998
02468
1012141618
0-0 30-30 60-60 90-90 120-120
Fertilizer mixture (P2O5 - K2O), lb/A
Cys
ts /
100c
c
0
5
10
15
20
25
30
Yield
respo
nse, %
C/C S/S C/S Yield response
Cultivar resistantto SCN races 3 and 4Cultivar resistantto SCN races 3 and 4
Yield response
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
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
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