Influence of low light intensity on growth and yield of four soybean cultivars during wet and dry seasons of northeast thailand

doi:10.4236/as.2011.22010

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Vol.2, No.2, 61-67 (2011)

doi:10.4236/as.2011.2 2010

Agricultural Sciences

Influence of low light intensity on growth and yield of

four soybean cultivars during wet and dry seasons of

Northeast Thailand

Anan Polthanee*, Khanistha Promsaena, Anucha Laoken

Department of Plant Science and Agricultural Resources, Faculty of Agriculture, Khon Kaen University, Khon Kaen, Thailand;

*Corresponding Aut hor: panan@kku.ac.th

Received 28 September 2010; revised 23 February 2011; accepted 2 March 2011.

ABSTRACT

Crop is commonly grown in intercrop combina-

tions of which cereal/legumes are the most

widespread in tropical countries . The availability

of low light intensity due to shading is the critical

factor in determining legume yield in intercrop-

ping. The experiment searches of better soybean

cultivar for intercropping. A field experiment was

conducted at the experimental farm of Khon

Kaen University in 2005. The objectives of this

study were to determine the influence of light

regimes (30% of normal light, 50% of normal light

and normal light) o n the grow th and yield of four

soybean cultivars (early, medium and late matur-

ity) under art ificial shadin g at 35 da ys after seed-

ing until harvest in the w et and dr y seasons. The

results showed that grain yield was significantly

(p < 0.05) decreased und er the low light intensit y

at 30% of natural light both in wet and dry season.

This was mainl y due to lo w light intensit y at 30%

of natural light decreasing the number of pods

per plant in the dry season. For cultivars, grain

yield was significantly difference (p < 0.05)

among cultivars both in the wet and dry seasons.

The cultivar KKU 74 (medium maturity) gave

maximum grain yield both in w et and dr y season

under the low light at 30% of natural light. The

KKU 74 cultivar is better adapted to shading en-

vironment than other cultivars. This was due to

the KKU 74 cultivar produced higher chlorophyll

b concentration in leaves after the plant experi-

enced to shading. This physiological character

can be used for soybean breeding program in

shading tolerance. Therefore, the cultivar KKU 74

had a higher potential yield advantage in inter-

cropping systems in which low light intensity is a

major l imi ti ng fa ct or on gra i n y i eld.

Keywords: Chlorophyll Concentration; Shading;

Soybean

1. INTRODUCTION

Intercropping can be used by small farmers primarily

to increase the diversity of their products and the stabil-

ity of their annual output through effective use of land

and other resources [1,2].

Grain yield of soybean decreasing, when inter cropped

with maize has been reported [3-5]. The low yield in in-

tercropped soybean as compared to monoculture is mainly

due to shading resulting in weak plant growth [6-8].

The reduction in light reaching the legume canopy

when intercropped with maize was about 30% - 50% of

the total incoming radiation and began around 30 - 35

days after maize seeding [9-11].

The grain yield of soybean reduced under the low

light because of reduction in dry matter production [12],

total pod number per plant [8,12,13] and thousand grains

weight [5]. To obtain the maximum yield of the intercrop

soybean under low light stress, selection of suitable

soybean cultivar plays an important role for intercrop-

ping systems. The cultivars may respond to shading

stress di- fferently in terms of growth and yield.

The objectives of this study were to determine the in-

fluence of light regimes (30% of normal light, 50% of

normal light and normal light) on the growth and yield

of 4 soybean cu ltivars under artificial shading in the wet

and dry seasons.

2. MATERIALS AND METHODS

2.1. Establishment and Management

The experiments were conducted in a field on well-

drained (Oxic Paleustult) sandy loam soil at the experi-

mental farm, Faculty of Agriculture, Khon Kaen Univer-

sity in the wet season (June-October 2005) and dry sea-

son (November 2005-February 2006). The four soybean

cultivars (determined by growth habit) were; Nakhon-

sawan 1 (NKS 1), Chiangmai 60 (CM 60), Khon Kaen

A. Polthanee et al. / Agricultural Sciences 2 (2011) 61-67

University 74 (KKU 74) and Ratchamongkol 1(RCM 1).

They were seeded on 16 June 2005 in the wet season and

on 9 November 2005 in the dry season.

Plot size was 6 × 4 meters, spaced 50 × 20 cm be-

tween row and plants oriented on a south-north direction,

and hand thinned to 2 plants per hill at 10 days after

seeding. Preplant fertilizer grade 12-24-12 (N, P2O5,

K2O) was applied to rows at a rate of 156 kg/ha. Control

of insects and weeds were given as needed during the

growing season according to Department of Agriculture,

Ministry of Agriculture and Cooperative Recommenda-

tion [14]. A sprinkler irrigation system was used in the

dry season trial.

2.2. Experimental Treatments

The experiment was arranged in a split plot design

with four replications. Light regimes as a main-plot con-

sist of (i) shade for 70% of normal light, (ii) shade for

50% of normal light and (iii) no-shade control (normal

light). Soybean cultivars as a sub -plot consist of the cul-

tivar NKS 1 (early maturity), CM 60 (medium maturity),

KKU 74 (medium maturity) and RCM 1 (late maturity).

In the present study, shading conditions for the respec-

tive level of light intensity were created from 35 days

after seeding until maturity. The early cultivar (NKS 1),

medium cultivar (CM 60, KKU 74) and late cultivar

(RCM 1) were subjected to shade stress at growth stages

of R3, R2 and R1, respectively. The unshaded plot served

as a control. The shade shelters were framed with poly-

vinylchloride pipe 5 cm in diameter, and covered with

black shade cloth prov iding a 70% and 50% reductio n of

natural light. The shelter was 60 m in length, 4 m in width,

and 2 m in height. The meteorological data of the ex-

perimental site in the wet and dry seasons are shown in

Table 1 and Table 2.

2.3. Measurements

Eight plants were randomly selected outside the har-

vesting area to determine leaf area at 50% flowering and

to calculate the leaf area index (leaf area/ground area).

At harvest, eight plants were randomly selected outside

the harvesting area to record plant height, shoot dry

weight, the number of pods per plant, the number of

seeds per pod and 100 seeds weight. Grain yield was

recorded from 50 random plants in the harvesting area.

Chlorophyll concentration was determined from leaves

sampled from uppermost fully expanded main stem

leaves at 30 day after shading by a spectrophotometric

met hod [15].

Table 1. Meteorological data throughout the growing period (rainy season of 2005).

Total Total

Average temperation Precipitation Radiation

Week Date

Max. (˚C) Min. (˚C) (mm) ( MJ/m2/d )

1 1 Jun.-7 Jun. 34.1 26.1 1.3 132.3

2 8 Jun.-14 Jun. 33.5 26 4.3 95.6

3 15 Jun.-21 Jun. 34.7 25.5 64.3 122

4 22 Jun.-28 Jun. 32.1 24.5 50.2 91.3

5 29 Jun.-5 Jul. 32.5 24.8 54.9 96.4

6 6 Jul.-12 Jul. 33.5 24.6 16.4 110.1

7 13 Jul.-19 Jul. 34.8 24.7 21.3 127.2

8 20 Jul.-26 Jul. 31.1 24.6 41.4 82.3

9 27 Jul.-2 Aug. 32.2 24.8 1.7 95.2

10 3 Aug.-9 Aug. 32.6 2 5.1 14 96.3

1 1 10 Aug. -16 Aug. 31.6 2 4.6 15.2 8 9.5

12 1 7 Aug.-2 3 Aug. 32.1 24. 1 50.5 89. 5

13 2 4 Aug.-3 0 Aug. 33.6 24. 2 53.1 1 08.1

14 31 Aug.-6 Sep. 31.7 24.3 95 101.4

15 7 Sep.-13 Sep. 29.9 24 140.6 74.7

16 14 Sep.-20 Sep. 31.2 24.1 33.1 90.1

17 21 Sep.-27 Sep. 32.5 24.5 103.6 88.5

18 28 Sep.-4 Oct. 32.6 25.1 5 114.5

19 5 Oct.-11 Oct. 31.6 24 3.1 113.5

20 12 Oct.-18 Oct. 32.7 24 0 122.4

21 19 Oct.-25 Oct. 32.4 22.8 0 109.5

22 26 Oct.-31 Oct. 32.8 22.9 0 99

A. Polthanee et al. / Agricultural Sciences 2 (2011) 61-67

Table 2. Meteorological data throughout the growing period (dry season of 2005).

Total Total

Average temperature Precipitation Radiation

Week Date

Max. (˚C) Mim. (˚C) (mm) (MJ/m2/d)

1 1 Nov. 05-7 Nov. 05 32.9 23.1 3.5 92.9

2 8 Nov. 05-14 Nov. 05 33.8 24.2 10.7 94.5

3 15 Nov. 05-21 Nov. 05 31 21.4 0 98.1

4 22 Nov. 05-28 Nov. 05 29.6 17.7 0 96.9

5 29 Nov. 05-5 Dec. 05 32.5 21.1 0 95.2

6 6 Dec. 05-12 Dec. 05 30 19.9 0 100.1

7 13 Dec. 05-19 Dec. 05 26.6 14.9 0 98.9

8 20 Dec. 05-26 Dec. 05 27 16.5 1 77.9

9 27 Dec. 05-2 Jan. 06 31.4 19.3 0 99.9

10 3 Jan. 06-9 Jan. 06 30.8 18.3 0 105.6

11 10 Jan. 06-16 Jan. 06 32.8 16.9 0 109.7

12 17 Jan. 06-23 Jan. 06 33.1 18.6 0 113.3

13 24 Jan. 06-30 Jan. 06 29.9 15.9 0 113.4

14 31 Jan. 06-6 Feb. 06 32.9 19.2 0 115.3

15 7 Feb. 06-13 Feb. 06 29.5 18.8 6.4 93.3

16 14 Feb.06-20 Feb. 06 32.8 21 13.4 105.4

17 21 Feb.06-27 Feb. 06 34.2 21.6 0 125.8

3. RESULTS AND DIS CUS SION

3.1. Growth

3.1.1. Leaf Area Index

In general, leaf area index (LAI) was not significantly

influenced by the shading treatments at 50% flowering

both in wet and dry seasons (Table 3). However, the LAI

decreased, ranging from 4 to 7% under the low light in-

tensities in the wet season but similarly to unshaded

control in dry season trials. The results of the present

study are in contrast with earlier report. Low lig ht inten-

sity increased the leaf area in potato [16] and Pongamia

pinnata [17]. For cultivars, the LAI was significantly

different (p < 0.05) among soybean cultivars in both wet

and dry seasons ( Table 3). The cultivar RCM 1 gave the

maximum LAI (6.3) in the wet season. The cultivar CM

60 gave the highest LAI (2.7) in the dry season. These

results indicated that the late cultivar with longer vegeta-

tive growth had a higher LAI than the early cultivar in

the wet season but not in the dry season.

3.1.2. Plant Height

The plant height was significantly influenced (p <

0.05) by the shading treatments at harvest in the wet but

not in the dry season trial (Table 3). The plant height

increased, ranging from 10 to 24% under the low light in

the wet season regarding shading level. In the present

experiment the plant height was significan tly different (p

< 0.05) among soybean cultivars in both wet and dry

season (Ta b l e 3 ). The cultivar RCM 1 gave the highest

plant height (114 cm) in the wet season, while the KKU

74 gave the maximum plant height (53 cm) in the dry

season.This result indicated that soybean growth in the

wet season gave higher plant height than in the dry sea-

son. This was due to light intensity in the wet season

being lower than in the dry season. The cultivar RCM 1

gave the highest plant height in the wet season. This was

due to the longer vegetative growth period of the late

maturity cultivars.

In the present experiment, however, the cultivar RCM

1 (late maturity) and cultivar KKU 74 (medium maturity)

did not show any significant difference in plant height in

the dry season.

The plant height in rice increased by 31% under low

light intensity was reported by Jadhav [18]. In contrast,

reduction on shoot length of Pongamia pinnata by 24%

in shade has been reported [17].

3.1.3. Shoot Dry W eight

The shading treatments did not show any significant

difference on the shoot dry weight of soybean at harvest

(Table 3). However, the shoot dry weight decreased,

ranging from 18% - 23% and 15% - 32% under the low

light intensities in the wet and dry season, respectiv ely.

Shading decreased shoot dry weight of soybean com-

pared with the unshaded control as reported earlier by

Kakiuchi and Kobata [12, 13], Saito and Kato [19], and

reduced dry matter yield in rice [20]. For cultivars, the

shoot dry weight was significantly different (p < 0.05)

among soybean cultivars (Ta ble 3). The cultivar RCM 1

produced the maximum shoot dry weight of 2288 kg·ha–1

in the wet season and 77 9 kg·ha–1 in the dry season. This

A. Polthanee et al. / Agricultural Sciences 2 (2011) 61-67

Table 3. Influence of light intensity on leaf area index at 50% flowering, plant height and shoot dry weight at har-

vest of soybean in wet and dry seasons 2005-2006.

Leaf area index Plant height (cm) Shoot dry weight (kg/ha)

Cultivar 100% 50% 30%100% 50%30% 100% 50% 30%

Wet season

NKS 1 4.0 4.1 4.8 67.9 58.966.9 1139.6 961.4 1061.3

CM 60 5.8 6.2 4.1 83.6 92.5102.92346.0 2247.5 1771.9

KKU 74 5.4 5.1 5.1 83.1 101.999.9 2164.4 2230.8 1771.9

RCM 1 6.8 5.9 6.2 94.0 108.5138.82646.3 2036.9 2178.8

LSD (Shading) 11.52

LSD (Cultivar) 1.44 22.27 1052.20

Shading (S) NS ** NS

Cultivar (C ) ** ** **

C × S NS NS NS

Dry season

NKS 1 2.0 1.9 2.0 33.7 35.131.1 489.4 390.6 444.1

CM 60 2.7 2.7 2.5 41.5 46.240.8 705.6 768.1 563.8

KKU 74 2.6 2.4 2.9 50.6 54.953.3 750.6 740.0 680.0

RCM 1 2.8 2.7 2.5 51.8 50.846.6 925.6 628.1 782.7

LSD (Cultivar) 0.50 6.64 20.36

Shading (S) NS NS NS

Cultivar (C ) ** ** *

C × S NS NS NS

was due to the cultivar RCM 1 having the highest leaf

area index in comparison with the other cultivars. The

cultivar RCM 1 had the longest interval for seeding days

to flowering (data not shown).

3.2. Yield Components

3.2.1. Number of Pods per Plant

The number of pods per plant was significantly influ-

enced by the shading treatment in wet but not in dry

season trials (Table 4). The number of pods per plant

decreased by 32% and 14% under low light intensity at

30% and 50% of natural light, respectively, in the wet

season. For the dry season , the number of pods per plant

reduced by 21% and 17% under the low light intensities

at 30% and 50% of natural light, respectively. Shading

reduced the number of pods per plant for soybean as

reported by Kurosaki and Yumoto [21] and Kakiuchi and

Kobata [12,13]. In terms of cultivar, the number of pods

per plant was significantly different (p < 0.05) among

soybean cultivars in wet and dry season (Ta b l e 4 ). The

cultivar CM 60 (medium maturity) produced the maxi-

mum number of pods per plant (92 pods·plant–1) in the

wet season and the cultivar RCM 1 (late maturity) gave

the highest number of pods per plant (49 pods·plant–1) in

the dry season. This result indicates that although the

medium and late cultivars were subjected to shading for

longer than the early cultiv ars, the potential adv antage to

produce the number of pods per plant was obtained for

the longer growth cycle cultivar. Considering shading

regime, the cultivar CM 60 gave the maximum number

of pods per plant under the low light at 30% and 50% of

natural light in the wet season, while the cultiv ar RCM 1

gave the highest number of pods per plant under low

light at 30% and 50% of natural light in the dry season.

3.2.2. Number of Seeds per Pod

The number of seeds per pod was significantly influ-

enced (p < 0.05) by the shading treatment in dry season

but not in wet season (data not shown). The number of

seeds per pod decreased by 7% and 8 % under low light

intensities at 30% and 50% of natural light, respectively

in the dry season. This agrees with the work done by

Egli [22]. In the wet season, the number of seed s per pod

was similarly under low light at 30 % and 50% of natural

light in comparison with normal light. The number of

seeds per pod w as not influenced by the shade treatment

as reported by Kakiuchi and Kobata [12,13].

3.2.3. Seed Weight

The shading treatment had no influence on the 100

seeds weight of soybean both in wet and dry season tri-

als (Ta b l e 4 ). There was a significant difference of 100

seeds weight among cultivars (Table 4 ). The results of

the present study are in agreement with earlier reports by

Kakiuchi and Kobata [12,13]. In contrast, shading re-

duced seed size as reported by Egli [22].

3.2.4. Grain Yield

The grain yield was significantly decreased (p < 0.05)

under low light at 30% of natural light both in wet and

dry seasons, but not at 50% of natural light (Table 4).

The grain yield reduced by 25% in the wet season and

37% in the dry season under low light at 30% of natural

light and reduced by 10% and 27% in wet and dry sea-

sons, respectively, under shading at 50% of natural light.

This was due to a significant decrease in the number of

pods per plant i n the wet seas on and t he nu mber of seeds

per pod in the dry season at 30% of natural light.

A. Polthanee et al. / Agricultural Sciences 2 (2011) 61-67

Table 4. Influence of light intensity on yield and yield components of soybean in wet and dry seasons 2005-2006.

Pod number 100 seeds weight (gm) Yield (ton/ha-1)

Cultivar 100% 50% 30%100% 50%30%100% 50% 30%

Wet season

NKS 1 44.2 44.6 43.521.6 21.221.02.7 2.7 2.6

CM 60 114.4 99.2 62.414.9 15.915.64.9 4.9 3.1

KKU 74 68.1 48.1 44.121.1 19.820.54.6 4.0 3.2

RCM 1 74.6 67.0 54.818.8 18.618.94.2 3.2 2.9

LSD (Shading) 16.13 0.88

LSD (Cultivar) 16.60 1.19 0.88

Shading (S) * NS *

Cultivar (C ) ** ** **

C x S NS NS NS

Dry season

NKS 1 29.9 21.5 19.523.7 23.823.92.0 1.4 1.3

CM 60 48.1 41.8 33.216.9 17.016.32.6 1.8 1.4

KKU 74 36.7 32.0 31.820.5 19.218.22.3 1.8 1.7

RCM 1 52.2 45.6 47.618.6 18.418.82.9 2.1 1.6

LSD (Shading) 0.68

LSD (Cultivar) 10.31 1.56 0.27

Shading (S) NS NS **

Cultivar (C ) ** ** *

C x S NS NS NS

That shading decreased seed yield of soybean has

been earlier reported [12,13,21,22]. For cultivars, grain

yield was significantly different (p < 0.05) among soy-

bean cultivars (Table 4). The grain yield reduced by 6%

- 37% in the wet season and 25% - 44% in the dry sea-

son at 30% of natural light, depending on cultivar. The

cultivars NKS 1 and KKU 74 gave minimum yield re-

duction by 6% and 25% in the wet and dry seasons, re-

spectively, at 30% natural light. With shading at 50% of

natural light, the cultivars CM 60 and KKU 74 gave

minimum yield reduction by 0.1% and 23% in wet and

dry seasons, respectively. In terms of potential yields

advantage, the cultivar KKU 74 gave maximum grain

yields of 3.2 and 1.7 ton·ha–1 in wet and dry seasons,

respectively under shading at 30% of natural light, while

the cultivar CM 60 produced the highest grain yield of

4.9 ton·ha–1 in the wet season and the cultivar RCM 1

gave the maximum grain yield of 2.1 ton·ha–1in the dry

season under shading at 50% of natural light.

These results indicate that the cultivar KKU 74 has a

higher potential yield advantage when grown in artificial

shade than other cultivars. Further research under actual

field conditions of corn-soybean intercropping systems

using four soybean cultivars should be investigated un-

der the competition for light, nutrients and water be-

tween the two crops.

3.2.5. Chlorophyll Concentration

The total chlorophyll content in leaves was not af-

fected by the shading treatment in both wet and dry sea-

sons. However, the total chlorophyll content tended to

increase in the shaded treatments (data not shown). In-

crease of total chlorophyll content in leaves by shade

was also reported by Naidy and Swamy [17] and Mut-

huchelian et al. [23]. The increased pigment content of

shade leaves has been attributed to the increase in the

number and size of chloroplasts, the amount of chloro-

phyll per chloroplast and better grana development [24].

In general, the shade leaves had a lower photosynthetic

rate due to the lower activity of photosynthetic enzy mes,

RuBP carbox ylase [25]. In the present exper iment, KKU

74 cultivar gave the high est chlorophyll b (2.18 mg/c m2)

concentration in leaf after the p lant experienced to shad-

ing 30 days (data not shown). In additio n, the increase in

chlorophyll b concentration before soybean experienced

to shading (35 days after seeding) and after shading 30

days in KKU 74, NKS 1, CM 60 and RCM 1 cultivars

was about 66%, 63%, 56% and 42%, respectively. This

associated with the adaptation of leaves to the low light

environment to intercept more light energy [26,27], or

with a decreased chlorophyll degradation rate [28]. This

physiological character can be used as criteria for soy-

bean breeding program in shading tolerance.

3.2.6. Relationship between Shoot Dry Weight

and Y ield

Shoot dry weight is a dominant factor for yield. The

higher shoot dry weight resulted to the higher in branch

number and consequently pod number per plant. In the

present experiment, soybean grown in wet season pro-

duced higher seed yield than in the dry season. This was

due to shoot dry weight of soybean in wet season was

higher than in the dry season (Figure 1). The days of

seeding to flowering of soybean in wet season were

longer 20 days than in the dry season.

In the present experiment, cultivar differed in res-

ponse of yield to shading, the KKU 74, CM 60 and

RCM 1 gave a similar in seed yield, but the three of so y-

A. Polthanee et al. / Agricultural Sciences 2 (2011) 61-67

y = 1.7791x + 786.45

= 0.8765

1000

2000

3000

4000

5000

050010001500 2000 25003000

Yield (kg/ha)

Wet

Dry

NKS 1

y4 = 1 .746x + 671 .3

2 = 0.8984

1000

2000

3000

4000

5000

050010001500 20002500 3000

Yield (kg/ha)

Wet

Dry

CM 60

Shoot dry weigh (kg/ha) at harvest Shoot dry weigh (kg/ha) at harvest

y = 1 .5449x + 786.62

= 0.9249

1000

2000

3000

4000

5000

050010001500 20002500 3000

Yiel d (kg/ha)

Wet

Dry

KKU 74

y = 0. 9008x + 1435.7

= 0. 7302

1000

2000

3000

4000

5000

05001000 1500 2000 2500 3000

Yield (kg/ha)

Wet

Dry

RCM 1

Shoot dry weigh (kg/ha) at harvest Shoot dry weigh (kg/ha) at harvest

Figure 1. The relationship between shoot dry weight and grain yield of 4 cultivars.

y = 1.0761x - 0. 0975

= 0.2869

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.1

1.2

0.60.650.70.750.80.85 0.90.9511.05

Relative yield (Control=1)

Wet

Dry

NKS 1

y = 0.9571x - 0.0828

R2 = 0 .3359

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.1

1.2

0.600.650.70 0.750.800.850.90 0.95 1.001.05

Relative yield (Control= 1)

Wet

Dry

CM 60

Relative shoot dry weight (control = 1) Relative shoot dry weight (control = 1)

y = 1. 2 434x - 0.3419

= 0.5696

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.1

1.2

0.6 0.65 0.7 0.750.80.850.9 0.9511.05

Relative yield (Control= 1)

Wet

Dry

KKU 74

y = 0.9849x - 0.052

= 0.4942

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.1

1.2

0.600.65 0.700.75 0.800.85 0.900.95 1.001.05

Relative yiel d (Control=1)

Wet

Dry

RCM 1

Relative shoot dry weight (control = 1) Relative shoot dry weight (control = 1)

Figure 2. The relationship between relative shoot dry weight and grain yield of 4 cultivars.

bean cultivars were significantly higher in seed yield

then NKS 1 cultivar. This was due to the three soybean

cultivars longer vegetative growth period than NKS 1

cultivar. In term of adaptation, the KKU 74 cultivar

seems to be better adapted to shading stress than the

other cultivars (Figure 2). Yield reduction due to shad-

ing in comparison with control in this cu ltivar was lower

an that of other cultivars (Figure 2).

y = 1.2434 x – 0.3419

R2 = 0.5696 y = 0.9849 x – 0.052

R2 = 0.4942

y = 1.7791 x + 786.45

R2 = 0.8765

y = 1.746 x 71.34 + 6

84 R2 = 0.89

y =6.62 1.5449 x

R2 = 0.9249 + 78y =7 0.9008 x + 1435.

.7302 R2 = 0

y = 1.0761 x – 0.0975

R2 = 0.2869 y28 = 0.9571 x – 0.08

R2 = 0.3359

Relative yield (Control = 1)

A. Polthanee et al. / Agricultural Sciences 2 (2011) 61-67

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