A model of soybean growth under competition
for light with common cocklebur
By Yecai Liu
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Ir
Himeo Series #2321
: BHA Series #39
Yecai Liu
I A Hodel··of
soybean growth undom
, competition for light with common
, cocklebur
I NAHE
. DATE
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A MODEL OF SOYBEAN GROWTH UNDER COMPETITION FOR
LIGHT WITH COMMON COCKLEBUR
By Yecai Uu
11
A research project submitted to the Graduate Faculty of
North Carolina State University
in partial fulftllment of the
requirement for the degree of
Master of Biomathematics
Department of Statistics
,.
.
Raleigh
1994
ABSTRACT
"
Yecai Liu. A model of soybean growth under competition for
light with common cocklebur
(under the direction of Dr.
G.
G.
Wilkerson) .
Five
treatments
soybeans alone,
cocklebur,
competition
considered
in
this
study:
'Essex'
'Young' soybeans alone, cocklebur alone, Essex +
Young
for
were
+
cocklebur.
light
was
A simple
developed.
model
This
of
model
interspecies
was
based on
radiation information under assumption of adequate water, nutrients
and no extreme temperature during the growing season. Total weight
above ground, stem weight and leaf weight were simulated .
•
Field data indicated soybean height, diameter and V-stage were
not affected by competition for light with cocklebur of low density
(0.83
plant/m2 ) .
Dry matter
growth
of
soybean
was
reduced by
competition in the simulation. Competition for light with cocklebur
could vary between soybean varieties. Growth of Young was reduced
less than that of Essex when competition occurred. The model is
sensitive to weed density. The simulation indicated that soybean
dry matter growth was reduced only slightly when weed density was
less than 1.0 plant/m2 ,
but was reduced dram~tically when weed
density was greater than 2.0 plant/m2 • CocklebuL dry matter growth
was underestimated seriously when competition occurred,
but it
could be improved by allowing a larger extinction coefficient early
in the growing season. A long period of low PAR could cause problem
since respiration was not adjusted by temperature in this model.
ACKNOWLEDGEMENTS
The author wishes to express appreciation to his
Advisory Committee: Drs. R. E. Stinner (chairman), G. G.
Wilkerson and H. J. Gold. They provided valuable advice and
encouragement throughout the degree program.
The author is grateful to Dr. Wilkerson for her
guidance and assistance in completing this project. The
author is also grateful to Mr. Gregory S. Buol. He and Dr.
Wilkerson provided the weather and field data for this
study. It would not have been completed without their help .
•
ii
TABLE OF CONTENTS
•
LIST OF TABLES
iv
LIST OF FIGURES
v
Introduction
1
Ma terial s and Methods
4
Description of the Model
1)
2)
3)
4)
5)
6)
Structure model equations
Photosynthesis
Respiration
Partitioning coefficients
Senescence
Efficiency of conversion
Resul ts and Discussions
1) Effect of competition for light with common
cocklebur on vegetative growth of soybean .....
2) Effect of competition for light with soybean
on vegetative growth of common cocklebur
3) Simulated results for dry matter growth of
soybean and cocklebur
a) Simulated results using Raleigh data
b) Simulated results using Smithfield data
6
6
8
10
11
12
13
14
14
16
17
18
20
Cone I us ion
22
Literature Cited
23
Figures
25
,.
iii
LISTS OF TABLES
Page
TABLE
1
Initial values for soybean and common cocklebur.
5
2
Initial values for weed of different density with
soybean competition.
5
Fitted functions for height, diameter and V-stage
growth of Essex variety.
15
Fitted functions for height, diameter and V-stage
growth of Young variety.
15
Fitted functions for height, diameter and V-stage
growth of common cocklebur.
17
Dry matter measurement of soybean with and without
common cocklebur competition.
51
Dry matter measurement of common cocklebur with and
without soybean competition.
51
3
4
5
6
7
:
iv
LIST OF FIGURES
FIGURE
Page
1
Height growth for Essex and Young varieties.
25
2
Diameter width growth for Essex and Young Varieties.
26
3
V-stage development of Essex and Young varieties.
27
4
Height growth of cocklebur with Essex and Young
competition.
28
Diameter width growth of cocklebur with Essex and
Young competition.
29
V-stage development of cocklebur with Eosex and
Young competition.
30
Comparison of maximum and minimum temperature for
the two weather stations.
31
8
Comparison of rainfall for the two weather stations.
32
9
Comparison of calculated PAR for the two weather
stations.
33
5
6
7
10
Stimulated dry matter growth for Essex (Raleigh data). 34
11
Stimulated dry matter growth for Young (Raleigh data). 35
12
Stimulated dry matter growth for common cocklebur
(Raleigh data) .
36
Stimulated dry matter growth for Essex with varied
weed density (Raleigh data) .
37
Stimulated dry matter growth for Young variety with
varied weed density (Raleigh data) .
38
13
14
15
Stimulated dry matter growth for common cocklebur with
Essex competition (Raleigh data) .
39
16
Dry matter growth for common cocklebur with Young
competition (Raleigh data) .
40
Stimulated dry matter growth for Essex
(Smithfield data) .
41
17
v
18
•
19
20
21
22
23
24
25
26
•
Stimulated dry matter growth for Young variety
(Smithfield data) .
42
Stimulated dry matter growth for cocklebur
(Smithfield data) .
43
Stimulated dry matter growth for Essex
weed density (Smithfield data) .
w~th
varied
44
Stimulated dry matter growth for Young 'with varied
weed density (Smithfield data) .
45
Stimulated dry matter growth for common cocklebur
with Essex competition (Smithfield data) .
46
Stimulated dry matter growth for common cocklebur
with Young competition (Smithfield data) .
47
Dry matter growth for Essex (Raleigh data, K=1.0
for weed) .
48
Dry matter growth for Young (Raleigh data, K=l.l
for weed) .
49
Dry matter growth for cocklebur (Raleigh data)
(K=1.0 for weed alone & with Essex, K=l.l for weed
grown with Young)
50
vi
LISTS OF TABLES
.
TABLE
Page
1
Initial values for soybean and common cocklebur.
5
2
Initial values for weed of different density with
soybean competition.
5
Fitted functions for height, diameter and V-stage
growth of Essex variety.
15
Fitted functions for height, diameter and V-stage
growth of Young variety.
15
Fitted functions for height, diameter and V-stage
growth of common cocklebur.
17
Dry matter measurement of soybean with and without
common cocklebur competition.
51
Dry matter measurement of common cocklebur with and
without soybean competition.
51
3
4
5
6
7
..
,.
iv
A model of soybean growth under competition for
light with common cocklebur
Introduction
Common cocklebur is a short-day plant that flowers and sets
seeds when the critical night length is reached. Most of the
seeds germinate and emerge. Consequently, a given area may be
continually reinfected unless long-term weed control is applied
(Bloomberg et al., 1982). A single common cocklebur may grow to a
height of 1.52 meters, and occupy a space of 4.3 meters in radius
and 2.9 meters soil depth. It often emerges simultaneously with
soybean (Barrentine et al., 1974). Common cocklebur grows taller
than soybean later in the season. In addition to maintaining
leaves above the soybean canopy, common cocklebur maintains
actively growing leaves below the top of the soybean canopy
throughout the growth season as a result of leaf development from
axillary buds along the lower main stems (Regnier et al., 1988).
Common cocklebur is a strong competitor with soybean for
available water, light, and nutrients (Bloomberg et al., 1982),
and it is
one of the worst broadleaf weeds on soybean farms in
the southeast (Barrentine et al., 1974).
Soybean growth and yield are reduced when competition with
weeds occurs. The reduction of soybean growth and yield depends
..
on the density of weeds. Yield reduction is from 3% to 88%,
depending on weed species and density (Barrentine et al., 1974;
1
Haggood et al., 1981; Bloomberg et al., 1982; Beckett et al.,
•
1988; Wilkerson et al., 1990; Wilkerson et al., 1991). Common
cocklebur has more leaves within the soybean canopy than
jimsonweed or velvetleaf (Regnier et al., 1989a), and it is a
stronger competitor for soybean. In addition to affecting soybean
yield, competition may have an effect on soybean height,
diameter, dry weights and leaf area. When water is not a limiting
factor, soybean yield is affected most by common cocklebur
competition, otherwise, soybean vegetative growth is affected
most by common cocklebur competition (Bloomberg et al., 1982).
The best indicators of competition effects are leaf area index,
plant dry weights, and yield of soybean. Soybean height is not
affected by competition (Cordes et al., 1984). Common cocklebur
has an average influence area of 0.5 square meters in soybean.
When the area of interference from adjacent
common cocklebur
plants overlap, the cumulative influence is additive. Also,
common cocklebur is reduced by 50% to 90% in size with soybean
interference (Henry et al., 1989).
Competition for light, water, and nutrients have a large
effect on soybean and common cocklebur growth. When water and
nutrient availability is not a limiting factor, competition for
light is dominant. Light is one of the key factors in
photosynthesis, therefore, it has a significant effect on dry
matter production. Both the percent light interception and the
rate of dry matter production increase with leaf area development
until they reach maximum and remain constant; the rate of dry
matter production is linearly related to the percent light
2
..J,'
interception for soybean (Schibles and Weber, 1965). Dry weight
is linearly related to cumulative intercepted photosynthetically
active radiation for four potato cultivars, and estimates of
daily light interception can give a reasonable prediction of
daily biomass growth of potatoes (Manrique et al., 1991).
Competition for light is one of the major factors causing soybean
yield loss (Stoller & Woolley, 1985; Regnier et al., 1989b;
Wilkerson et al., 1990). Some models of competition for light
between weed and crop have been developed. A deterministic model
(Spitters & Aerts, 1983) called Weed-Crop simulates the
competition between crop and weed for light and water. The model
indicates crop biomass and yield are reduced because of
competition. Another model of interspecies competition for light
(Rimmington, 1984) describes the interceptionof light by the
component species, and calculates the rate of dry matter
production of each component species. Therefore, the effect of
competition for light among species can be determined. SOYWEED
(Wilkerson et al., 1990) is a simulation model of crop/weed
competition which could be used to investigate the effect of
competition for light and water between soybean and cocklebur.
Competition for light only occurs within an 'area of influence'
in this model.
When LTCOMP (Wiles & Wilkerson, 1991) is
incorporated into SOYWEED and vertical leaf distribution is
considered, the result of simulation of weed and crop growth is
improved.
3
The objectives of this model are:
1) To determine the effect of competition for light on soybean
and common cocklebur vegetative growth.
2) To determine the effect of competition for light on dry matter
production for soybean and common cocklebur.
3) To determine the difference in competition for light with
common cocklebur for the two soybean varieties: Essex and Young.
4) To determine the effect of weed density on soybean dry matter
growth.
5) To determine if a simple model can adequately describe
competition for light between a crop and a low density weed
population.
Materials and Methods
The field experiment was established in May, 1992 at Clayton,
North Carolina by Dr. G. G. Wilkerson at Crop Science Department
at NCSU. A completely randomized block design with four
replications and five treatments was used. The five treatments
were: Essex alone, Young alone, common cocklebur alone, Essex +
common cocklebur, and Young + common cocklebur. Soybeans were
planted in rows 0.90 meters apart. Common cocklebur alone were
also planted in rows 0.90 meters apart. Common cocklebur grown
with soybean were planted 1.25 meters apart within soybean rows.
One border row was placed between sample rows. Plots were
irrigated to minimize competition for water. Height, diameter,
4
roo
and V-stage of soybean and common cocklebur were measured every
week after emergence. Destructive samples were taken four times
during the growing season, and total dry weight above ground,
leaf dry weight, stem dry weight, leaf area, and leaf specific
weight were also determined. The initial values for soybeans and
common cocklebur were calculated based on plant density, average
seed weight and partitioning factors for each species (Table 1.).
Table 1. Initial values for soybean and common cocklebur.
Treatment
Density
(plants/m2 )
Essex alone
Essex + Weed
Young alone
Young + Weed
Weed alone
Weed + Essex
Weed + Young
16.16
13.57
19.89
17.61
9.84
0.83
0.83
Whole plant
Canopy
Stem
Leaf
0.198
0.166
0.248
0.219
0.049
0.004
0.004
0.946
0.796
1.183
1. 045
0.221
0.019
0.019
(g/m2)
2.200
1.850
2.750
2.430
0.492
0.041
0.041
1.144
0.962
1.430
1.264
0.271
0.023
0.023
Table 2. Initial values for weed of different density with
soybean competition.
Density
(plants/m2 )
0.345
0.414
0.518
0.691
1. 036
2.072
4.144
9.840
10.36
*
Whole plant
*
0.0174
0.0207
0.0259
0.0346
0.0518
0.1036
0.2072
0.4920
0.5180
Canopy
Stem
Leaf
0.0096
0.0114
0.0142
0.0190
0.0285
0.0570
0.1140
0.2710
0.2849
0.0017
0.0021
0.0026
0.0035
0.0052
0.0104
0.0207
0.0490
0.0518
0.0078
0.0093
0.0116
0.0156
0.0233
0.0466
0.0932
0.2210
0.2331
(g/m2 )
weed alone.
5
•
In order to determine the effect of weed density on soybean
growth, the initial values for weed with different density were
also determined (Table 2.).
Parameters used in this model were estimated from the 1992
data and obtained from the literature (Wilkerson et al., 1983;
Wilkerson et al., 1990; Wiles & Wilkerson, 1990; Kiniry et al,
1992) .
Description of the Model
Crop growth is a result of the interaction "of its genetic
constitution and its environment. The weather conditions of the
growing season have a major effect on crop development. The
quantitative relationship between weather information and crop
development is an interesting subject to modelers (France and
Thorny, 1984). Dry matter production of soybean can be predicted
based on radiation information under assumption of no extreme
temperature, adequate water and nutrients during the growing
season (Jones and Boote, 1987).
1) Structure model equations:
Soybean plants consist of leaf, stem, shell, seed, and root
components. Photosynthesis converts CO 2 to carbohydrate (CH20).
Some CH20 is converted to plant tissues and some is used in
respiration to maintain existing tissues. Organ growth rates are
described by partitioning carbohydrate (CH20) to each component
6
and utilizing CHzO in synthesis and respiration. Plant components
are described as grams of dry matter per square meter of ground
area. The growth model can be established by describing the rate
changes of dry matter components resulting from photosynthesis,
respiration, tissue synthesis and senescence. First order
nonlinear differential equations are applied to describe the
change of dry matter rates for the major components. These
equations are from SOYGRO (Wilkerson et al, 1983).
The overall soybean dry matter in g/m2 is described as:
-~)
dW/dt = Ei (Pg
SI - Ss
-
where dW/dt is the growth rate of overall plants, Pg is
photosynthesis,
~
is the maintenance respiration, and Ei is the
efficiency of conversion for CH20 to dry matter.
In order to represent dry matter accumulation in vegetative
plant parts, the following equations are used:
dW/dt
=
dWs!dt
dWr!dt
where
=
d~/dt,
*
Ei (Pg
-
~)
-
SI
Xs * Ei (Pg
-
~)
-
Ss
-
~)
-
Sr
XI
Xr
*
Ei (Pg
dWs/dt, dWr/dt are the growth rates for leaf, stern,
and root respectively.
~,
Xs'
~
are the partitioning
coefficients for leaf, stern, and roots respectively, they depend
on the physiological development of the crop. Roots are
considered as a sink for CHzO and are not included in the
calculation of maintenance respiration.
7
The model structures for common cocklebur are similar to
those for soybean (Wilkerson et al, 1990):
dW' /dt
= E'·(P'
1
g -R')
m
- 8' I - 8' 8
dW'l/ dt
dW' Jdt
dW'Jdt = X'r * E'i (P'g - R'm) - 8'r
where dW' /dt, dW'l/dt, dW' Jdt, dW' Jdt are the overall dry
matter, leaf, stem, and root growth rates respectively. X'I' X' 8'
X'r are the partitioning coefficients for leaf, stem, and roots
respectively. E'i is the efficiency of conversion.
2) Photosynthesis:
The primary effect of light competition is its influence on
photosynthesis. Photosynthesis is reduced as light interception
decreases. The daily gross photosynthesis rate per unit ground
area of soybean canopy or common cocklebur is calculated by the
following formula:
where pmug is the maximum potential photosynthesis rate of
soybean or common cocklebur. FI is the proportion of the
available light intercepted (Wilkerson et al, 1990). The
relationship between Prnug and PAR developed by Ingram and
colleagues (1981) is used to calculate Prnug:
p rnug
1.67*PAR -0.0173*PAR2
o
<= PAR <= 48.27
and
PAR > 48.27
8
•
The percentage of direct light penetrating a layer of crop
canopy, integrated over a day has been described by an
exponential function (Schibles & Weber, 1965):
I/I o
=
exp(-K*L)
where I o is the irradiance above the canopy, I is irradiance
below the canopy, K is the extinction coefficient and L is the
leaf area index of the canopy. Light interception by a canopy can
be approximated as the difference between
the light intensity
below and above the canopy. Total interception is computed
assuming independence in the probability that a light beam will
strike either crop or common cocklebur (Wilkerson et al., 1990):
1-I/Io
=
1-exp(-K*L-K'*L'))
where 1-I/Io is the proportion of direct light intercepted by the
mixed canopy (soybean and common cocklebur), K and K'
are the
extinction coefficients for soybean and common cocklebur, Land
L' are the leaf area indices for soybean and common cocklebur
respectively. The extinction coefficient for soybean is assumed
as 0.61 (Wiles & Wilkerson, 1991). The
coeffiqi~nt
for common
cocklebur is assumed as 0.90 (Kiniry et ai, 1992). Both are
assumed to be the same for the entire growing season.
One of the major differences between LTCOMP and this model is
the assumption of leaf distribution. Three-layer model and a
triangular function were used to model the effects of the
vertical leaf structure in LTCOMP, but uniform and identical leaf
distribution for soybean and cocklebur within the mixed canopy is
assumed in this model. Based on the above assumption, the
proportion of light interception by soybean can be determined by
9
the following formula:
~
= (l-I/I o }*K*L/(k*L+K'*L').
The percentage of light interception by common cocklebur is
F' t
(l-I/I o ) *K' *L' / (k*L+K' *L') .
During the early growth period, competition between common
cocklebur and soybean for light is small since leaves are not
thoroughly intermingled horizontally. To avoid underestimation of
early growth, no interspecies competition for light is assumed
until the total leaf area index of soybean and common cocklebur
is greater than 1.0.
Competition for light occurs within an 'area of influence'
around each weed in SOYWEED (Wilkerson et aI, 1990). In order to
simplify the model structure, it is assumed that competition
occurs in the whole canopy area in this model.
Leaf area index is calculated by the
L
L'
following formulas:
Wt*SLA and
= W't *SLA'
where SLA and SLA' are the specific leaf areas for soybean and
common cocklebur respectively. They were estimated from the 1992
data; 0.0029 m2 /g for Essex, 0.0032 m2 /g for Young, and 0.0019
m2/g for common cocklebur.
3} Respiration:
A two component model (McCree, 1974)
respiration:
Rm
= R1 *W + R2 *Pg ,
where
Rm
is used to describe the
is the integrated daily
10
respiration, Pg is the total of daily gross photosynthesis, and W
is the total dry mass of living tissue. R1 and R2 are functions of
temperature (McCree, 1974):
R1=24*R1,30* (0.044+0.0019 *T+O. 001 *T2 )
R2 =24*R2,30* (0.044+0.0019 *T+O. 001 *T2 )
where R1,30 equals to 3.5*10-4, and R2,30 equals to 0.004 (Wilkerson
et al 1983), T is the daily temperature. The daily temperature in
the growing season is assumed as 30°C to simplify the model
structure.
4) Partitioning coefficients:
Only vegetative dry matter growth is considered in this
model. The partitioning coefficients for dry matter accumulation
are needed to estimate the dry matter growth for each part of
soybean and cocklebur. They are changed during the growing
season. These partitioning coefficients for soybean and common
cocklebur were obtained from SOYWEED (Wilkersqn et aI, 1990). The
partitioning coefficients for soybean leaf can be determined by
their relationship with V-stage:
Xl = 0.43
0.43-0.0114*V-stage
0.31
1.5 <= V-stage
1.5 < V-stage < 10.5
V-stage >= 10.5
where Xl is the partitioning coefficient for soybean leaf. The
partitioning coefficients for soybean stem are determined by
V-stage too:
Xs = 0.09+0.04*V-stage
V-stage <= 10.5
11
~
= 0.51
V-stage> 10.5
where Xs is the partitioning coefficient for soybean stem. The
partitioning coefficients for soybean total weight above ground
can be determined as
~
= XI + XS '
where
~
is the partitioning
coefficient for soybean total weight above ground.
The partitioning coefficients for common cocklebur are
obtained from SOYWEED and they are determined by days after
emergence (Wilkerson et al, 1990):
X'I = 0.45
X'I
0.70 - 0.0068*Days
Days => 36
36 < Days <= 90
X'I = 0.08
Days > 90
X's
0.10 + 0.0084*Days
r>ays <= 90
X's
0.86
Days > 90
X't
X'I + X's
where X'I' X's and X't are partitioning coefficients for weed leaf,
stem and total weight above ground.
5) Senescence:
A lot of factors such as leaf aging, water stress,
competition for light, and protein remobilization can have an
effect on soybean and common cocklebur leaf senescence. Leaf
senescence of soybeans is handled in this model as a function of
V-stage. Leaf senescence starts when V-stage is equal to 5, and
increases linearly to 6% of leaf weight when V-stage is equal to
15:
SI = (-0.03+0.006*V-stage)*WlI where SI is leaf senescence for
12
soybean,
~
is the leaf weight for soybean. The petiole
senescence, Sp is assumed to 50% of SI based on the assumption
that a petiole weighs 0.5 times as much as the leaf attached
(Hanway & Weber, 1971). Leaf senescence for common cocklebur S'lt
is estimated as a function of days after emergence. Leaf
senescence begins at 136 days after common cocklebur emerges, and
S'I
is assumed to be 15% of leaf weight later in the growing
season (Wilkerson et ai, 1990). The weather data used in this
model does not reach 136 days and it is assumed that no
senescence for cocklebur during this early period.
6) Efficiency of conversion:
The efficiencies of conversion for soybeans are different
among components: 0.66 for leaf, 0.71 for stem, and 0.79 for
root. The efficiency of conversion for common cocklebur is
assumed to be 0.68 for all components for the whole growing
season (Wilkerson et ai, 1983; Wiles & Wilkerson, 1990).
13
Results and Discussion
1) Effect of competition for light with common cocklebur on
vegetative growth of soybean.
Soybean height and diameter with and without common cocklebur
competition for light were fitted by nonlinear functions. Soybean
V-stages
were fitted by linear functions (Tab+e 3 & 4). These
functions fitted the data well and all had a R2 of greater than
0.9l.
Competition for light with weed had little effect on height
growth of Essex and Young varieties (Figure 1). In general, both
Essex and Young were taller than common cocklebur early in the
growing season (Figure 1), and competition for light with common
cocklebur had little effect on them. Once Essex and Young reached
mature status and height growth stopped, common cocklebur
surpassed them. Therefore, competition for light with common
cocklebur did not affect soybean height growth under moderate
weed density (0.83 plants/m2 in this study).
Canopy diameter of Essex and Young varieties was not affected
by cocklebur competition (Figure 2). This was expected given a
low weed density in this study (0.83 plant/m2 ) . When competition
is strong (weed density is high), both soybean and common
cocklebur have a relatively small diameter (Herry & Bauman,
1989) .
14
Table 3. Fitted functions for height, diameter and V-stage
growth of Essex.
Function
Height/alone
1/ (0.01010+0. 3514 0 *e-O· 06S *oayS)
0.9899
Height/cocklebur
1/ (0.00997+0. 37622*e-O·06S *oayS)
0.9849
Diameter/alone
1/ (0.01149+0. 42663*e-O.07S *oayS)
0.9962
Diameter/cocklebur = 1/ (0.01151+0.41138 *e-O•07S *oayS)
0.9929
V-stage/alone
-2.3010 + 0.20269*Days
0.9122
V-stage/cocklebur
-2.1033 + 0.20076*Days
0.9160
..
Table 4.
Fitted functions for height, diameter, and V-stage
growth of Young.
Function
Height/alone
1/ (0.00817+0.38431 *e-O.063 'Day S)
0.9841
Height/ cocklebur
1/ (0.00771+0. 40633*e-O.06S *oay S)
0.9902
Diameter/alone
1/ (0.01058+0.40912 *e-O•075 *Oap
)
0.9950
Diameter/ cocklebur = 1/ (0.01077+0.38013 *e-O.07S *oayS)
0.9959
V-stage/alone
-3.4244 + 0.2377*Days
0.9749
V-stage/cocklebur
-4.3555 + 0.2565*Days
0.9732
Competition for light with common cocklebur did not have an
obvious effect on soybean V-stages (Figure 3). The soybean
15
V-stage has been shown to be most affected by cumulative
temperature (Jones and Boote, 1987). Competition for light with
common cocklebur did not change the soybean growth pattern during
the vegetative phase covered in this study.
2) Effect of competition for light with soybean on vegetative
growth of common cocklebur.
The vegetative growth of common cocklebur was fitted by
nonlinear functions and linear functions (Table 5). All of these
functions had high R2 and they appeared to fit the data well.
Common cocklebur height growth was not affected very much by
soybean competition except for the last two data points (Figure
4). Since the weed density for weed alone was larger than for
weed grown with soybean (Table 1), the increase of height for
common cocklebur alone in the late growing season might be due to
intraspecies competition.
Early in the growing season, competition with soybean did
not influence common cocklebur diameter growth since the
competition was weak. Later in the season, cocklebur diameter
growth was decreased. Diameter growth of cocklebur with Young
appeared to be affected more by competition than was that of
cocklebur with Essex (Figure 5).
The V-stages of common cocklebur were not affected by soybean
competition (Figure 6). Since temperature is the primary factor
affecting V-staging rate (Jones and Boote, 1987), competition for
light with soybean should have little effect on it.
16
Table 5. Fitted functions of height, diameter and v-stage growth
of common cocklebur.
Function
Height/Alone
1/ (0.00756+0. 50722*e-o.os*oayS)
0.9843
Height/Essex
1/ (0.00913+0. 45066*e-o.os *oayS)
0.9944
Height/Young = 1/ (O.00829+0.39031*e-o.os *oayS)
0.9948
Diameter/Alone = 1/ (0.00950+0. 48676*e-O.07S *oayS)
0.9853
Diameter/Essex
1/ (0.01009+0. 51802*e-O· 07S *oayS)
0.9816
Diameter/Young
1/ (0.01064+0. 45547*e-O•07S *oayS)
0.9863
V-stage/Alone
-3.9846 + 0.2615*Days
0.9726
V-stage/Essex
-4.0122 + 0.2725*Days
0.9794
V-stage/Young
= -4.0077 + 0.2764*Days
0.9687
The competition effects for light of the two soybean
varieties on common cocklebur showed a little difference. In
general, Young had a stronger effect both on common cocklebur
height and diameter since Young was taller and wider than Essex.
3) Simulated results for dry matter growth of soybean and
cocklebur.
Two weather datasets from two weather stations close to
Clayton were used to estimate the PAR since the weather
17
information for Clayton was not available for 1992. These two
stations were located in Raleigh and Smithfield, North Carolina.
They were about 20 miles from Clayton. The temperatures appeared
to be similar (Figure 7), but some differences existed for
rainfall (Figure 8). PAR was estimated based on temperature and
rainfall. Actual PAR at Clayton could be different from the
calculated PAR. Although the calculated PAR were similar, some
differences were obvious. The calculated PAR for Smithfield
appeared to be greater than for Raleigh, especially late in the
period (Figure 9).
These two estimated PAR datasets were used to simulate
soybean and common cocklebur dry matter growth. Total weight
above ground, stem weight and leaf weight were simulated.
a) Simulated results using Raleigh data.
Total weight above ground, stem weight and leaf weight for
Essex were reduced when competition for light with common
cocklebur occurred. At the early stage, since there was no
competition, or just weak competition, dry matter growth for
Essex alone and Essex with common cocklebur were similar. The
reduction for dry matter growth of Essex with common cocklebur
competition increased late in the season. The simulated data
corresponded closely to field data for total weight above ground
and stem weight, but leaf weights were overestimated. The trend
was obvious: competition for light with common cocklebur would
reduce dry matter growth of Essex (Figure 10).
18
Total weight above ground, stem weight and leaf weight for
Young were reduced when competition for light with common
cocklebur was increased. The simulated data did not respond
closely to the field data. Total weight above ground for Young
alone was overestimated at the early stage, but underestimated
alone at late stage. Total weight above ground for Young grown
with weed was overestimated. Leaf weights for Young were over
estimated for the whole period (Figures 11).
The simulated data fit the field data well for common
cocklebur alone, but underestimated common cocklebur grown with
soybean. The dry matter growth for weed alone and weed grown with
soybean were different since their densities were not the same
(Table 1). The field data also showed the differences. Weed grown
with Essex and Young had the same density. Young reduced common
cocklebur dry matter growth more than Essex did in the
simulation, but the field data showed little differences (Figure
12) •
This model is very sensitive to weed density on soybean dry
matter growth. The simulated data showed that soybean dry matter
growth was reduced only slightly when weed density was less than
1.0 plant/m2 , but was reduced dramatically whe~ weed density was
greater than 2.0 plant/m2 (Figure 13 and 14).
The effects of competition with common cocklebur appeared to
be different on soybean varieties. Young dry matter was reduced
less than Essex when competition occurred (Figures 13 and 14) .
The result indicates that competition for light with common
cocklebur can vary between varieties. In general, Young grew
19
taller and wider than Essex in this experiment. Therefore, Young
was a stronger competitor and could get more sunlight during the
late vegetative growing period than Essex.
Dry matter growth of cocklebur of different densities with
soybean competition was simulated. The simulatted data indicated
that weed dry matter growth was increased as weed density
increased. However, dry matter growth for weed alone was greater
than weed grown with soybeans. The effects of competition for
light with Essex and Young on common cocklebur were different.
Dry matter of weed grown with Young was less than weed grown with
Essex since Young was taller and wider (Figure 15 and 16). Young
also had more leaf area than Essex since specific leaf area (SLA)
of Young was larger than that of Essex. Young appeared to be a
stronger competitor for cocklebur.
The soybean had a negative dry matter growth during period of
85 to 88 days from planting. The negative growth was due to the
;"t
low PAR value (below 8 E/m2 ) . When the photosynthesis rate was
less than respiration rate, a negative growth would occur since
the model was not adjusted by temperature and rainfall. If a long
period of low PAR occurred, simulated data would be seriously
biased from field data because of the negative growth.
b) Simulated results using Smithfield data.
In general, the simulated data were similar as from the
Raleigh data since the calculated PAR were similar. The simulated
data were greater in the late stage because Smithfield had a
higher calculated PAR values than Raleigh (Fi9;ures 17 to 23) .
20
Growth of Cocklebur with soybean was seriolisly
underestimated. The simulation for cocklebur could be improved
(Figure 26) by allowing a larger cocklebur extinction coefficient
(K'=1.0 for cocklebur with Essex and K'=l.l for cocklebur with
Young), but the simulation for cocklebur alone was overestimated
and soybean with weed was underestimated (Figures 24, 25 and 26) .
It appeared that allowing a larger extinction coefficient for
cocklebur only during the early growing season would help to
improve the simulation. Since different extinction coefficients
for cocklebur under Essex and Young competition were needed in
order to fit the field data, some other factors might have an
effect on the output of this model. In SOYWEED (Wilkerson et al
1990), competition for light occurs only within an 'area of
influence' around each weed. LTCOMP (Wilkerson et al 1990)
incorporated into SOYWEED, a three-layer model is used to
describe the main effects of vertical structure of the mixed
canopy. Water supply and respiration adjusted by temperature are
also considered in SOYWEED. The uniform and identical leaf
distribution, competition for light occurring in the whole canopy
area, no extreme temperature, and adequate water and nutrient
supplies during the growing season are some of the basic
assumptions in this model. The simulation indicates that they can
be the major concerns.
21
Conclusion
Soybean height, diameter width and V-stage were not affected
by competition for light with common cocklebur of low density
(0.83 plant/m2 in this study). Dry matter growth of soybean was
reduced by competition. The simulated data responded closely to
the field data for Essex and common cocklebur alone, but
underestimated Young and common cocklebur grown with soybean.
This result indicated that this simple model can reflect soybean
growth under weed competition appropriately. The long period of
low PAR have a effect on this model. The simulation showed that
assumptions of competition for light in the whole canopy area and
uniformly leaf distribution structure can cause bias from the
field data.
22
Literature cited
Barrentine, W. L., and L. R. Oliver. 1977. Competition, threshold
levels, and control of cocklebur in soybeans. Mi.ssissippi Agric.
and For. Exp. Stn. Tech. Bull. 83.
Beckett, T. H. and E. W. Stoller. 1988. Volunteer corn (Zea mays)
interference in soybeans (Glycine max). Weed Sci. 36:159-166.
Bloomberg, J. R., B. L. Kirkpatrick & L. M. Wax. 1982.
Competition of common cocklebur (Xanthium Pensylvanieum) with
soybean (Glycine Max.). Weed Sci. 30:507-13.
Cordes, R. C. and T. T. Bauman. 1984. Filed competition between
ivyleaf morningglory (Ipomea bederacea) and soybeans (Glycine
max). Weed Sci. 32:364-370.
France, J. & J. H. M. Thorny. 1984. Mathematical Models in
Agriculture. PP 335. Butterworth & Co Ltd.
Hagood JR., E. S. JR., T. T. Bauman, J. L. Williams, JR. and M.
M. Schreiber. 1981. Growth analysis of soybeans (Glycine max) in
competition with jimsonweed (Datura stramonium). Weed Sci.
29:500-504.
Hanway, J. J. and C. R. Weber. 1971. Dry matter accumulation in
eight soybean {Glycine Max (L.)) varieties. Agro. J. 63:227-230.
Herry, W. T. and T. T. Bauman. 1989. Interference between
soybeans (Glycine max) and common cocklebur (xathium strumarine)
under Indiana field conditions. Weed Sci. 37:753-760.
Ingram, K. T., D. C. Herzog, K. J. Boote, J. W. Jones and C. S.
Barfield. 1981. Effects of defoliating pests on soybean canopy
CO2 exchange and reproductive growth. Crop Sci. 21:961-968.
Jones, J. W. & K. J. Boote. 1987. Simulation models for soybean
and other crops. Food & Fertilizer Technology Center. Technical
Bulletin. No. 106. 1-7.
Kiniry, J. R., J. R. Williams, P.W. Gassman and P. Debaeke. 1992.
A general, process-oriented model for two competing plant
species. Transactions of The ASAE. Vol. 35(3) :801-810.
McCree, K. J. 1974. Equations for the rate of dark respiration of
white clover and grain sorghum, as functions of dry weight,
photosynthetic rate, and temperature. Crop Sci. 14:509-514.
Manrique, L. A., J. R. Kiniry, T. Hodges and D. S. Axness. 1991.
Dry matter production and radiation interception of potato. Crop
Sci. 31:1044-1049.
23
Regnier, E. E. and E. W. Stoller. 1989a. The effects of soybean
(Glycine max) interference on the canopy architecture of common
cocklebur (Xanthium strumarium), jimsonweed (Datura strumonium),
and velvetleaf (Abutilon theophrasti). Weed Sci. 37:187-195.
Regnier, E. E., E. W. Stoller, and E. D. Nafziger. 1989b. Common
cocklebur (Xanthium strumarium) root and shoot interference in
soybeans (Glycine max). Weed Sci. 37:308-313.
Rimmington, G. M. 1984. A model of the effects of interspecies
competition for light on dry-matter production. Aust. J. Plant
Physiol. 11:277-286.
Shibles, R. M. & C. R. Weber. 1965. Leaf area~ solar radiation
interception and dry matter production by soybean. Crop Sci.
5:575-577.
Spitters, C. J. T. and R. Aerts. 1983. Simulation of competition
for light and water in crop-weed associations. Aspects Applied
BioI. 4:467-483.
Stoller, E. W. and J. T. Woolley. 1985. Competition for light by
broadleaf weeds in soybeans (Glycine max). Weed Sci. 33:199-202.
Wiles, L. J. and G. G. Wilkerson. 1990. Modeling competition for
light between soybean and broadleaf weeds. Agri. Systems. 35:3751.
Wilkerson, G. G., J. W. Jones, K. J. Boote, K. T. Ingram, & J. W.
Mishoe. 1983. Modeling soybean growth for crop management. Trans.
ASAE, 26:63-73.
Wilkerson, G. G., J. W. Jones, H. D. Coble & J. L. Gunsolus.
1990. SOYWEED: A simulation model of soybean and common cocklebur
growth and competition. Agron. J. 82:1003-1010.
24
..
Figure 1. Height growth for Essex and Young varieties.
Height (em)
Height (em)
>
120I
Treatment
-E
<
•••
>.. >.
120I
AE+ C
I
100I
•••
•••
•••
.
.
I
60I
b--
,
)'I
oy
..
Y+C
•••••••
<
••
• •••
••
. ..
.4
60I
••••
/
...
••••
•••••
....
-
•••
40I
/
o
•••
20I
...
•••
5 15 25 35 45 55 65 75 85 95
Days from planting
N
\J1
j
<
,
••••••••
v
i/
20I
'r"
--y+ c
A
80I
.
•••
40I
••••••••
A
-y
•• •••
.
j
Treatment
••
-E+C
80
-
-
•••••••
¢E
100I
~--,-
o
••••
....
••••
•
<
5 15 25 35 45 55 65 75 85 95 105
Days from planting
..
.
•
Figure 2. Diameter width growth for Essex and Young varieties.
Diameter width (em)
Diameter width (em)
100·
I
Treatment
-y
80
<>y
--y+c
60
40
20
0'
5 15 25 35 45 55 65 75 85 85
Days from planting
N
0'
..,
5
15
25
35
45
55
65
75
Days from planting
85
95 105
.
"
Figure 3. V-stage development of Essex and Young varieties.
V-stage
25,
,
V-stage
25
~I~~""""-'--'''''''''-'--'~--------------------------------n·'
-y
-E
20hH
20
0 E
Oy
--y+ C
..... y+c
15
10
15
L
10
,
5
•••
> ••....
5
0
1
I
5 15
~
I»
25
35
45
55
65
Days from planting
75
85
95
0'
r
5
15
I
25
35
45
55
65
Days from planting
75
85
95
105
..
..
.
Figure 4. Height growth of cocklebur with Essex and Young competition.
HT (em)
HT (CIn)
1401
I
HTlcml
140
140
Treatment
-C
120
OC
Treatment
120
OC
100
-C+E
• C+ E
--C+Y
--c+ y
--C+ E
.... C+E
-c
100
"'C+Y
"'C+Y
80
15 25 35 45 55 65 75 85 95 105
Days from planting
N
\0
15 25 35 45 55 65 75 85 95 105
Days from planting
15 25 35 45 55 65 75 85 95 11:6
Days from planting
..
..
'
,
Figure 5. Diameter growth of cocklebur with Essex and Young competition.
DW(cm}
DW{cm)
110,
100
.1
, I
-c
looH 0 c
-c
Oc
--c+
120 1,
OW (em)
120·
,
-C+E
l00U • c+
E
E
--C+Y
..... C+ E
""'C+Y
~
10
oI~~~",,----,-~",,----,-,-,,-
o
w
o
10 10 30 40 00 60 10
~o
Days from planting
0'
~o
100
!
5 15 25 35 45 55 65 75 85 95 105
Days from planting
15 25 35 45 55 65 75 85 95 1(6
Days from planting
'll
t.
•
Figure 6. V-stage development of cocklebur with Essex and Young competition
V·stage
V-stage
~[
i
V-stage
·•·......· · > 1
30,
Treatment
j
.
i·'
• <r',.'<'.
30
Treatment
-c
25 1,' 0 c
25I
''''1
j
"'C+Y
..
•••
<> c+ E
--c+ y
"'C+Y
,.
j1f··l
.••. <
,
20I
•••
Vi
.. J
\
i
15 k ..
•••••
-C+E
--c+ y
20 t'. . .
....
<'">
Treatm ent
-c
25H 0 c
--c+ E
» .
15I
•••
V
')
10
.)
\<
10I
••
...
••••
J
5
••••
/
j.
5I
••••
i
/1
J!
0'
15 25 35 45 55 65 75 85
w
......
Days from planting
~5
105
/.
5 15 25 35 45 55 65 75 85
Days ftom planting
I
~5
105
o
I
>
....
5 15 25 35 45 55 65 75 85
Days bom planting
~5
105
I
..
"
Figure 7. Comparision of maximax and minimum temperature for the two weather stations.
Temperature
40,,.......
......
Weather Station
- Max. Temp-Raleigh
-0-
30
Max. temp-Smithfield
+Min. temp-Raleigh
-I-
20
10
0'
t
5
15
25
35
45
55
65
Days from planting
W
N
75
85
95
105
Min. temp-Smithfield
..
•
..
.
..
Figure 8. Comparision of rainfall for the two weather stations.
Rainfall (mm)
60
i
i
Weather Station
-Raleigh
50
40
-- Smithfield
.~
30
20 I>}}}>JIJ
10
Ot
,.:
5
w
w
15
os
~
25
35
45
".
55
65
Days from planting
75
85
I
95
1 05
..
•
.. .
Figure 9. Comparision of calculated PAR for the two weather stations.
Calculated PAR (E/m*
* 2)
==~=--==="""""""'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''-'-'''''''''-'------------- '''''''''''''''TT-'-'--'--'-'--'-01i
80 :,
Weather Station
-Raleigh
-- Smithfield
60
40
20
0'
i
5
w
.p-
15
25
35
45
55
65
Days from planting
75
85
95
105
.
•
. .
.
•
Figure 10. Simulated dry matter growth for Essex variety (Raleigh data).
Stern weight Iglmu 21
Total weight (g/m* * 2)
Treatment
-e
--e+ c
a
e
+ e+ c
~oo
loot.. ·.·.·.. ·.·.·.. ·.. ··.. ,1
ij "-=="""
~ l~ ~~ ~ ~ ~~ ~ 1~
W
lJ1
Ok::::
I
i
Days from planting
~
18 28 38 ~ 58 68 78
Days frOlll plantilg
1m
98
I
~ 1~ ~~ ~ ~ ~ ~ 1~ ~ ~
Oars from ~Ian~n~
..
•
..
.
..
Figure 11. Simulated dry matter growth for Young variety (Raleigh data).
Total weight above groung Ig/m" 21
Stem wci~tlg'mff 21
Treatment
-- young + weed
-young alone
150r:cc
c - .• ,
• young alone
+young + weed
100
0.........··
..
8 18 28 38 48 58 68 78 88 98
Days from planting
W
0'
0=»>
!
18 28 38 48 58 68 78 88 98
Days ~om planting
8 18 28 38 48 58 68 78 88 98
Days from planting
..
Figure 12. Simulated dry matter growth for common cocklebur (Raleigh data).
Total weight above ground Ig/m** 21
1,000'
lealweijltlwmu21
Stem w~~tlglmff21
i
250,
700
I
Treatment
600
-weed alone
200
. .weed +essex
500I
- weed +young
150
400I
•weed alone
300I
.
100
"'.'"
+weed +essex
200I
(
!
5Oh .• -•• ' • '
100I
0
8 18 28 38 48 58 68 78 88 98
1
;",..:::;:;....;'~-,,>,
Days from planting
w
-..,J
!»l
.......
"I
o
8 18 28 38 48 58
01
~
Days from ~lIlting
78 88
~8
....-<
Y2-.....> .............
8 18 28
_.
~:::~::~
»>
~ ~
58
~
Days bom planting
18 88
~8
weed +young
..
. . .
Figure 13. Simulated dry matter growth for Essex variety with weed competition (Raleigh data).
Tolal weight above ground Iglm ff 21
~alwei~tlg(mtt21
Stem weight (g(m t t 21
~I
I
200,
Wild DlIllty Ipllnll/ll" 21
-no weed
--0.346
-0.414
"'0.518
+0.691
*1.036
+2.072
xIOOf .••..•,'., .. ,-'. ,-' ......• ·--f
*4.144
. '\
+10.36
~
"AV\~
200h"U·'>-·
-\
I
Il
v
w
8 18 28 38 48 58 68 78 88 98
ex>
Days from planting
8 18 28 38 48 58 68 78 88 ~
8 18 28 ~ ~ 58 68 78 88 ~
Days from plantin~
Days from plantin~
·. .
Figure 14. Simulated dry matter growth for Young variety with varied weed densities (Raleigh data).
Tot~ w~ght above ground Iglm tf 21
Weed DllI1lity (planll/ml'ZI
-no weed
--0.345
-0.414
-0.518
~ooL"
+0.691
+1.036
-11-2.072
*4.144
+10.36
100
8 18 28 38 48 58 68 78 88 98
~
Days from planting
~
1~ l~ ~
48 ~~ 68 1~ ~ 9~
Days from ~Iantinl
~
1~ l~ ~ ~ ~~
68 1~ ~ 98
Days nom ~Iantinl
· .
..
.
Figure 15. Simulated dry matter growth for commom cocklebur grown with Essex variety (Raleigh data).
Total weight above ground Ig/m **21
leaf w~~tlg(mU 11
Stem wm~~tl~/mtf 1)
1~O
.'
Wood DIMity (pl."IIn· '21
I
- 9.841noc comp.l
-0.345
-0.414
100
-0.518
~oon
+0.691
+1.036
1~1
-<>-2.072
*4.144
+10.36
100
200 f>< ....
~I
100
8 18 28 38 48 58 68 78 88 98
Days from planting
oj>
o
8 18 18 38 48
~8
68 78 88 98
Days from ~Ian~n~
8 18 18 38 48
~
68 78 88 98
Days from ~Ian~ng
·
'.
Figure 16. Simulated dry matter growth for commom cocklebur grown with Young variety (Raleigh data).
Total wei~M a~ove ~round 1~/mf +II
~tem~~l(~~u11
laf Y19~t I~~ff 11
~I
I
w.... DlIllity (PlIII1I/.... 21
-9.84 (no comp.l
-0.346
I
-0.414
1001
-0.518
+0.691
..
ocrJ
/
I.·
...· •.
....
*1.036
-0-2072
(rJ
.', .... -.-.-.-.-"
-
1~
I
*4.144
+10.36
»J
100·· .
"·1
100
Tt
100
y
vr~
't " "
vnw••••
.j>
......
~ 1~ l~ ~~ ~ ~~ ~~ 1~ ~ 00
Da~s from ~an~n~
M
II'II',."
~ 1~ 1~ ~ ~ ~ ~ ~ ~ ~
Oaf! Hom ~Iiltm~
~ 1~
!
~ ~ ~ ~ 1~ ~
Oa~ frOOl ~Ian~
i
..
.. .
Figure 17. Simulated dry matter growth for Essex variety (Smithfield data).
Total weight (g/m* *2)
Leaf weight Ig/mu 21
Stem weight Ig/mtf 21
160.
...
i
Treatment
.~~
-e
140
--e+ c
• e
120
+ e+ c
300
80
200
60
100
40
100
20
o~
8 18 28 38 48 58 68 78 88 98
f;
Davs from planting
I
o
8 18 28 38 48 58 68 78 88 98
Days from planting
18 28 :m 48 ~ ~ 78 88 98
Days from planting
,
· . .
Figure 18. Simulated dry matter growth for Young variety (Smithfield data).
Total weight (g/m* *2)
Stili weight IglmU 21
Treatment
--Y+ C
-Y
300
1
a
Y
+ Y+ C
200
1oo~ • ,•• "•• "··"···"
OK
O'
8 18
-I>-
w
~8 ~
48 58
~8
78 88
Days from planting
~
18 28 38 48 58 68 78 88 98
DIYs tom ~lIIting
8 18 28 38
~ ~
08 78
Days iron pllltilg
~ ~8
..
.
.
Figure 19. Simulated dry matter growth for common cocklebur with Essex and Young (Smithfield data).
Total weight(g/m* * 2)
Stem we~ht Ig/mft 21
~l
1,000"
leaf weilht 1111Iff~1
I
l~"""", ,..,..,...,..,.,..,..,...,..,.,..,..,...,..,.,..,..,...,..,....,...,...,..,
Treatment
-c
. "c+ e
800
--c+ y
6(XW-c., ..
• c
+ c+ e
... c+ y
600
400
400
2oor·
01::
-:=:::::,:::.. ~:::~:::~:::.
8 18 28 38 48 58 68 78 88 98
t
Days from planting
I
o
~ l~ l~ ~ ~ ~~ ~~ 1~ ~ ~
Days troll ~lantitl
•
I
..
)
Figure 20. Simulated dry matter growth for Essex grown with varied weed density (Smithfield data).
'Total weight (g/m* *2)
Weed Oeneity (p1ente/m' '11
-0.345
- 'no weed
-0.414
-0.518
+0.691
+1.036
-2.072
*4.144
+10.36
100,· .. -
8 18 28 38 48 58 68 78 88 98
Days from planting
.j:V1
8 18 28 :i 48 58 68 78 88 98
Days fiom planting
8 18 l8 38 48 58 fa 78 M 98
Days from ~antin~
..
•
•
,.
Figure 21. Simulated dry matter weight for Young grown with varied weed density (Smithfield data).
~t8n w8~tlwmff ~l
Total weight (g/m* * 2)
Weed Den8ity (p1I1lI8/m* *2)
. -- ....
-0.345
~
. °no weed
-0.414
-0.5182
+0.691
IJ)•...
*1.036
-2.072
300
j
*4.144
)
~OO[····
200
+10.36
>"
'''I
100~···················
1oo~·
8 18 28 38 48 58 68 78 88 98
g;
Days from planting
1)0
"*.~
~
IJI
~ 1~
18
~ ~ ~~
fa
Daysm~ting
1~ ~
98
~ 1~ ~ ~ ~ ~
08 ~ ~ ~
Days 110m ~nlilt
I
.
t
.
,
•
,
..
,
.
"
.
Figure 22. Simulated dry matter growth for commom cocklebur grown with Essex (Smithfield data).
Total weight above ground Ig/m* *21
~tern wm~tl~/mff 11
leaf 1Y~~t( Wm" 11
~~I
I
Weed Denalty (pllnta/m" 2)
-9.84Ino comp.)
--0.345
-0.414
--0.518
+0.691
*1.036
"2.072
*4.144
+10.36
-i>
-.J
8 18 28 38 48 58 68 78 88 98
Days nom planting
~
1~ 1~
!
~ ~ ~ 1~ ~
Days ~om ~an~n~
!
~ 1~ ~
!
~ ~~ ~ 1~ ~ ~
Days ~om ~ntm~
,
.. ..
..
"II
~
Figure 23. Simulated dry matter growth for com mom cocklebur with Young variety (Smithfield data).
Total we9lt above ground Ig/m*' 21
Stem wei~t Ig/mlf 21
WIld Dlnlity (pllnllllm' • 21
-no weed
--0.345
-0.414
-0.518
-+- 0.691
.... 1.036
-0-
2.072
*4.144
+10.36
8 18 28 38 48 58 68 78 88 98
0f-
&;
Days fiom ~an~ng
8 18 28 38 48 58 68 78 88 98
Days from planting
8 18 28
~
48 58 68 18 88 98
Days from planting
•
..
.
t
l
'
,
•
•
J'.
•
,-'
J
I
•
~_.
w
Figure 24. Dry matter growth for Essex (Raleigh data, k= 1.0 for weed).
.,: •. ,..
...
':
,:>,,". ;":.:'"
''',,:,
~a ~i~~ (gfmt~l
Stem we~M twmtt2)
Total weight (g/m**2)
100..
."
I
Treatment
.'
:~:.i:.il:i! ..•lj_iii!.iiil~
oro) .,. . . H' .,.::.):
•••••
,"' ',..', , . ' ' ...
~ool
-e
--e+c
"" .".,,,,,,,,,,., .. ,,,,,,.,
D
>":':'·":·,X
"':::
_
H' 1:',
+ e+c
"
.,' - . >:.!··r/·Y:::-·:~%i!@!·!·1
.:"."
.:,.
H:.,··.·.4'
r&Y'
·"::f'<~·T!",\'\/~';::("';::, I
1,<",,<,:,:'/:""::.
300l
-.
I."" ..,,, .. , '.. ,
".
T
>_ .i .·:".j'!TII:"1.,!i1
:,~ :.: t
."",.
,,,
/1.'
2OOt- -
"
200
.',.f./..
100)
w
01:>0)
ij
o
8
8
m~
$ ~ n M~
Days from planting
~ ~
e
~ ~ ~ ~ ~ ~
Days lrom planting
n~
M
~
~ ~ ~ ~ ~ ~
ffi
D,IrOOl~
~ M 00
•
.
lo
~
..
"
,
,.
~.
1J
./'.
..... .
~
Figure 25. Dry matter growth for Young (Raleigh data, k= 1.1 for weed).
Total weight above groung (g/m**2)
&ern we~~ ~rntt21
leal wegnl Iwm**21
2001"".",·,,,,,,,,,·' ..
~.
.". ,... ·"··",,,1
Treatment
-.
-- young
+weed
- young alone
• young alone
+ young + weed
o
8 18 28 38 48 Ea
~
78 88 98
Days from planting
A
\0
8 18 28
~
48
~
68 78 88 98
Days from P~nDrrJ
o
8 18
~8 ~ ~ ~
fa 18 88 98
Days Irom panting
.
.
Figure 26. Dry matter growth for cocklebur (Raleigh data).
(k=1.0 for weed alone & grown with Essex, K=1.1 for weed grown with Young).
Total weight above ground (g/m**2)
&em wei~~ ~mtt~
8OOr-t
---:-:---:-:--------,
1,200 !:@·I.i·::··jilll:·.'/.i:':.!...::::·::,.:i:•• ·:;.:1.1::·::1.1::1
Treatment
-weed alone
roJl
. 'weed + essex
,.
-weed + young
2001
:
.
• weed alone
+ weed + essex
A
I~I . c . . . • : . , . •
0' . . _.;;;..;:::
8 18 28 38 48 58 68 78 88 98
Days from planting
re
~ ~ ~ ~
&n ~
~~.
~
~
re
e:' -.
.-
weed + young
._'.'.-0'.- ...... -".... . .. ··"""""1
~ ~ ~ ~
&n ~
~
~lrom~
Ul
o
....
.
,
.... \-,
.
~
..
•
"
....
~
..
"
A
..
•.
Table 6. Dry matter mesurement of soybean with and without common cocklebur competition.
Items
Mesurement Date
Essex Alone (g/m 2)
Essex
+ Cocklebur
Young Alone
Young
+ Cocklebur
Min.
Max.
Mean
Min.
Max.
Mean
Min.
Max.
Mean
Min.
Max.
Mean
Leaf Weight
7/14/1992
33.24
95.13
68.18
49.70
66.03
57.08
79.95
92.19
85.75
69.74
91.60
76.65
Stem Weight
7/14/1992
35.02
121.60
78.72
58.13
83.48
68.58
87.62
114.50
99.24
83.00
103.26
94.81
Total Weigt
7/14/1992
68.26
216.73
146.90
107.82
149.51
125.66
171.79
206.69
184.99
152.75
194.86
171.46
Leaf Weight
8/4/1992
121.69
149.64
138.30
103.52
125.39
119.52
138.79
192.53
159.51
97.41
134.34
124.32
Stem Weight
8/4/1992
203.93
245.56
220.08
159.59
210.00
187.85
232.43
397.37
299.67
155.03
270.14
228.49
Total Weigt
8/4/1992
335.73
398.45
358.38
272.60
345.12
307.37
371.22
589.90
459.18
252.44
398.43
352.81
Table 7. Dry matter mesurement of common cocklebur with and without soybean competition.
Items
Mesurement Date
Cocklebur Alone
Cocklebur
+ Essex
Cocklebur
+ Young
Min.
Max.
Mean
Min.
Max.
Mean
Min.
Max.
Mean
Leaf Weight
7/14/1992
26.20
139.13
72.03
8.29
22.92
17.18
7.88
19.03
13.45
Stem Weight
7/14/1992
18.98
147.46
73.54
5.73
24.72
17.03
6.66
19.49
12.43
Total Weigt
7/14/1992
45.18
286.58
145.57
14.02
47.64
34.21
14.55
38.52
25.88
Leaf Weight
8/4/1992
92.40
180.65
125.74
17.40
47.58
32.04
20.76
51.26
31.77
Stem Weight
8/4/1992
120.91
339.72
208.64
19.27
71.79
48.18
37.74
86.98
52.06
Total Weigt
8/4/1992
213.31
520.37
334.38
36.67
119.37
80.22
58.50
138.23
83.83
51