American Journal of Plant Sciences, 2013, 4, 2011-2014
http://dx.doi.org/10.4236/ajps.2013.410251 Published Online October 2013 (http://www.scirp.org/journal/ajps)
2011
Effect of Plant Spacing on Growth and Grain Yield of
Soybean
Bhagirath S. Chauhan*, Jhoana L. Opeña
Weed Scientist and Assistant Scientist, Weed Science, Crop and Environmental Sciences Division, International Rice Research In-
stitute, Los Baños, Philippines.
Received July 27th, 2013; revised August 29th, 2013; accepted September 15th, 2013
Copyright © 2013 Bhagirath S. Chauhan, Jhoana L. Opeña. This is an open access article distributed under the Creative Commons
Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is
properly cited.
ABSTRACT
In the Philippines, rice monoculture systems are common. Compared to these systems, the rice-soybean cropping sys-
tem may prove more water-efficient and there is a trend of increasing soybean area in the response to water scarcity and
need for crop diversification in the Philippines. A field study was conducted to evaluate the effect of row and plant to
plant spacing (20 × 10, 20 × 5, 40 × 10, and 40 × 5 cm) on growth and yield of soybean. Plant height was not influ-
enced by the plant geometry. Spacing, however, influenced leaf area and shoot biomass of soybean. Plants grown at the
widest spacing (i.e., 40 × 10 cm) produced lowest leaf area and shoot biomass at 6 and 12 weeks after planting. Leaf
area and shoot biomass at other three spacing were similar. There was a negative and linear relationship between weed
biomass and crop shoot biomass at 6 and 12 weeks after planting. Grain yield of soybean was not affected by plant ge-
ometry and it ranged from 1.3 to 1.9 t·ha−1 at different spacing.
Keywords: Row Spacing; Plant to Plant Spacing; Leaf Area; Weed Biomass
1. Introduction
In the Philippines, rice (Oryza sativa L.) is the most im-
portant source of food, where it is mainly grown after
intensive tillage in wet conditions. There are two seasons
(dry and wet) and farmers grow rice in both seasons. In
dry seasons, however, rice requires a huge amount of wa-
ter for puddling (repeated tillage in wet conditions called
puddling) and planting [1-3]. Farmers in Asia, including
the Philippines, are expected to have limited irrigation
water in the future to flood their rice fields [4]. There has
been an increasing and competing demand for other wa-
ter uses in urban areas. The risk of water scarcity may
lead to changes in production systems to bring about less
water demanding systems [5]. They may include dry-
seeded rice and crop diversification.
Soybean (Glycine max L.) is one of such crops, which
can be grown in dry seasons. Compared to rice monocul-
ture systems, the rice-soybean cropping system may prove
more water-efficient in the Philippines. At present, soy-
bean is not grown on a large area in the Philippines; how-
ever, there is a trend of increasing its area in the res-
ponse to water scarcity and need for crop diversification.
In different countries, soybean is grown at different
row spacing [6,7]. The row spacing in soybean can vary
from 19 to 76 cm [8]. Narrow row spacing is known to
suppress weed growth by closing crop canopy earlier
than wider row spacing [7,9,10]. Narrow row spacing
may also increase available moisture to the crop, for exam-
ple, corn (Zea mays L.) [11]. In soybean and corn, nar-
row row spacing was found to increase light interception
[6,12,13]. Soybean yield can also be influenced by the
plant to plant spacing within a crop row.
A computer search of published literature revealed that
there is limited information available on the effect of row
spacing and plant to plant spacing on the growth and
grain yield of soybean in the Philippines. Plant geometry
can also influence weed growth in the crop. A study was
therefore conducted to evaluate the effect of plant geo-
metry on the growth and yield of soybean at Los Baños,
Philippines.
2. Materials and Methods
The study was conducted at the farm of the International
Rice Research Institute, Los Baños, Laguna, Philippines.
*Corresponding author.

Effect of Plant Spacing on Growth and Grain Yield of Soybean 2012
The experimental site had a clay loam soil with a pH of
6.8 and organic carbon of 1.2%.
Two pre-sowing cultivations in dry soil conditions
were performed before crop planting. Soybean seeds
were planted by hand at four different plant geometries.
The row and plant to plant spacing were 20 × 10, 20 × 5,
40 × 10, and 40 × 5 cm. Phosphorus (P) and potassium
(K) were applied before crop planting at 40 kg P2O5 ha−1
and 40 kg K2O ha−1, respectively. Nitrogen (N) as urea,
was applied at 20 kg N ha−1 at 4 weeks after planting
(WAP) and 20 kg N ha−1 at 8 WAP. The crop was plant-
ed on January 22, 2013, after mixing seed with rhizobium
inoculant. The field was surface irrigated immediately
after planting.
A pre-emergence application of pendimethalin (1.0 kg
ai ha−1) was used at 1 d after planting (DAP) to control
weeds. After this, no weed control measures were taken.
Pendimethalin was applied with a knapsack sprayer that
delivered around 320 L·ha−1 spray solution through flat
fan nozzles. No control measures were taken for insect
and diseases.
In the field, the time taken for crop emergence, appea-
rance of the first unifoliate leaf, appearance of the first
trifoliate leaf, and start of flowering was observed. Im-
mediately after crop emergence, six consecutive plants of
soybean were tagged to measure their plant height and
numbers of trifoliate leaves. These growth parameters
were measured at 2, 4, 6, 8, and 10 WAP. Plant height
was measured from ground level to the main stem tips.
At 6 and 12 WAP, soybean plants in 1-meter row lengths
were sampled from two places to measure leaf area
(cm2·m−2) and shoot dry mass (g·m−2). The biomass was
measured after placing samples in an oven at 70˚C for 72
hours. At the same periods (i.e., 6 and 12 WAP), weed
biomass was also measured after taking samples from
two quadrats of 40 × 40 cm. Soybean was harvested on
April 30, 2013 from an area of 9.6 m2 and grain yield
was converted to t·ha−1 at 16% moisture content.
The experiment was laid out in a randomized complete
block design with three replications of each spacing
treatment. The leaf area, shoot biomass, and grain yield
data were analyzed using the least significant difference
(LSD) at 5% level of significance [14]. Plant height and
leaf number data taken throughout the season were fitted
to a three-parameter sigmoid model using SigmaPlot
10.0. A model,


0
1yаexWb 



 was used,
where y is the plant height or leaf (trifoliate) number at
timex, a is the maximum height (cm·plant−1) or leaf
number (plant−1), W0 is the time (WAP) required to reach
50% of the maximum height or leaf number and b is the
slope. The relationship between weed biomass (g·m−2)
and crop biomass (g·m−2) at 6 and 12 WAP was assessed
using linear regression analysis (SigmaPlot 10.0).
3. Results and Discussion
Soybean plants emerged at 4 DAP. The first unifoliate
leaf appeared at 6 DAP and first trifoliate leaf appeared
at 12 - 13 DAP. The crop started flowering at 42 DAP.
There was a trend of increasing plant height of soybean
at narrow row spacing and plant to plant spacing; how-
ever, it was statistically similar between treatments (Fig-
ure 1, Table 1). The maximum plant height (a) ranged
from 72 to 94 cm·plant−1. The rate of development (slope
b) of height was also similar. The time taken to reach
50% of the maximum height (W0) ranged from 4.9 to 5.8
WAP, and it did not differ between different spacing. A
previous study reported maximum heights of 107 to 117
cm for soybean and the time taken to reach 50% of the
maximum height was 7 to 8 WAP [15].
Weeks after planting
0246810
Height (cm plant-1)
0
20
40
60
80
100 20 x 10 cm
20 x 5 cm
40 x 10 cm
40 x 5 cm
(cm·plant−1)
Figure 1. Effect of plant geometry (row and plant to plant
spacing: 20 × 10, 20 × 5, 40 × 10, and 40 × 5 cm) on the
height of soybean. A three-parameter sigmoid model was
fitted to the height data over different times.
Table 1. Parameter estimates (standard error) of the three-
parameter sigmoid model fitted to the plant height and leaf
number data. The fitted model was



0





1yаexWb, where y is the plant height or
leaf number at time x, а is the maximum height (cm·plant−1)
or leaf number (plant−1), W0 is the time (WAP) required to
reach 50% of the maximum height or leaf number, and b is
the slope.
Spacing (cm)A b W0 R
2
Plant height
20 × 10 89.0 (9.7) 2.1 (0.4) 5.8 (0.6)0.99
20 × 5 94.0 (12.4)2.0 (0.5) 5.5 (0.8)0.98
40 × 10 72.2 (8.7) 2.1 (0.5) 5.2 (0.7)0.98
40 × 5 80.2 (8.1) 2.0 (0.4) 4.9 (0.6)0.98
Leaf (trifoliate) number plant−1
20 × 10 17.5 (1.1) 1.2 (0.3) 5.0 (0.3)0.95
20 × 5 12.6 (0.7) 1.2 (0.3) 4.3 (0.3)0.97
40 × 10 24.4 (0.5) 1.4 (0.1) 5.5 (0.1)0.99
40 × 5 16.2 (1.1) 1.2 (0.3) 4.8 (0.4)0.99

Effect of Plant Spacing on Growth and Grain Yield of Soybean 2013
The highest numbers of trifoliate leaves (24 plant−1)
were observed at 40 × 10 cm spacing and they were sig-
nificantly higher than those at other spacing (Figure 2,
Table 1). The plants at other three spacing produced 13
to 18 trifoliate leaves plant−1. The rate of leaf develop-
ment (slope b), however, was similar at different row and
plant to plant spacing. The plants grown at the narrowest
spacing (i.e., 20 × 5 cm) took 4.3 WAP to reach 50% of
the maximum leaf number plant−1, whereas the plants
grown at the widest spacing (i.e., 40 × 10 cm) took 5.5
WAP to reach 50% of the maximum leaf number plant−1
(Table 1).
Leaf area and shoot biomass of soybean were signifi-
cantly affected by the row and plant to plant spacing.
Plants grown at the widest spacing, that is 40 × 10 cm,
produced lowest leaf area and shoot biomass and this was
true at both sampling periods, that is 6 and 12 WAP (Ta-
ble 2). At 6 WAP, for example, soybean produced a leaf
area of 19,380 cm·plant−1 and a biomass of 95 g·m−2
when grown at 40 × 10 cm spacing. Compared to 6 WAP,
the leaf area reduced at 12 WAP and this was mainly due
to leaf senescence at crop harvest. Leaf area and shoot bi-
omass at other three spacing were similar.
Weeks after planting
0246810
Trifoliate leaves (no. plant-1 ) 0
5
10
15
20
25 20 x 10 cm
20 x 5 cm
40 x 10 cm
40 x 5 cm
Figure 2. Effect of plant geometry (row and plant to plant
spacing: 20 × 10, 20 × 5, 40 × 10, and 40 × 5 cm) on leaf pro-
duction (number plant−1) of soybean. A three-parameter
sigmoid model was fitted to the data.
Table 2. Effect of spacing (row and plant to plant) on leaf
area and crop biomass at 6 and 12 weeks after planting
(WAP).
Leaf area (cm2·m−2) Biomass (g·m−2)
Spacing
(cm) 6 WAP 12 WAP 6 WAP 12 WAP
20 × 10 30830 22380 149 778
20 × 5 38990 26070 198 710
40 × 10 19380 10700 95 517
40 × 5 24190 21220 174 730
LSD 8370 8750 51 145
There was a negative and linear relationship between
weed biomass and crop shoot biomass at 6 and 12 WAP
(Figure 3). The correlation explained 44% of the varia-
tion in weed biomass at 6 WAP and 49% of the variation
in weed biomass at 12 WAP. These results clearly sug-
gest that increasing weed growth could affect crop bio-
mass. By increasing crop biomass, a significant reduction
in weed biomass can be achieved [16].
Grain yield of soybean was not influenced by the plant
geometry (Figure 4). Grain yield ranged from 1.3 to 1.9
t·ha−1 at different spacing; however, the lowest grain
yield was produced by plants at 40 × 5 cm. The results of
this study suggest that plant spacing may influence leaf
area and shoot biomass of soybean. However, the differ-
ence among grain yield was not significant. Such results
y = 16.7 - 0.05x; R2 = 0.44
p = 0.02
050100 150 200 250
Weed biomass (g m-2)
0
4
8
12
16
20
y = 73.0 - 0.07x; R2 = 0.49
p = 0.01
Crop biomass (g m-2)
0200 400 600 800100
0
0
10
20
30
40
50
60
6 WAP
12 WAP
(g·m
−2
)
(g·m
−2
)
1000
Figure 3. Relation between weed biomass and crop shoot bi-
omass at 6 and 12 weeks after planting (WAP).
Row and plant to plant spacing (cm)
20 x 1020 x 540 x 1040 x 5
Yield (t ha-
1
)
0.0
0.5
1.0
1.5
2.0
2.5
(t·ha
−1
)
Figure 4. Effect of plant geometry (row and plant to plant
spacing: 20 × 10, 20 × 5, 40 × 10, and 40 × 5 cm) on grain
yield (t·ha−1) of soybean.

Effect of Plant Spacing on Growth and Grain Yield of Soybean 2014
suggest that soybean can be grown successfully at both
20 and 40 cm row spacing. Narrow row spacing, how-
ever, may help in closing canopy earlier than wider row
spacing. In a previous study, soybean planted in 18 cm
rows was more competitive against weeds than those in
76 cm wide rows [17]. Similarly, Knezevic and collea-
gues suggested that planting soybean in wider rows re-
duced early season crop tolerance to weeds requiring ear-
lier weed management programs than in narrower rows
[7]. In water limited environments, narrow row spacing
may enhance available moisture to soybean [11]. There is
a need to study further the effect of plant geometry on the
performance of different cultivars as cultivars differ in
their height, leaf morphology, etc.
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