effects of drought stress, planting density and geometry...

15 Sabeti et al.

Int. J. Biosci. 2014

RESEARCH PAPER OPEN ACCESS

Effects of drought stress, planting density and geometry on

vegetative characteristics and grain yield of rice

Ali Sabeti1*, Mojtaba Jafarzadeh Kenarsari2 , Ali Ashraf Jafari3

1Islamic Azad University, Science and Research Branch, Tehran, Iran

2Islamic Azad University, Naragh Branch, Naragh, Iran

3Research Institute Forests and rangelands, Tehran, Iran

Key words: Rice, drought stress, planting geometry, planting density.

http://dx.doi.org/10.12692/ijb/5.3.15-24

Article published on August 02, 2014

Abstract

This study was conducted to determine the effects of drought stress, planting density and geometry on rice using

a split-split plots design based on randomized complete block with 4 replications in 2010 to 2011. Factors were

drought stress, as main factor with 3 levels (normal irrigation and retain irrigation at plant height of 20-30 cm,

and 2 levels of water stress with 7 days interval between two successive irrigation in vegetative and reproductive

stages), planting geometry as sub factor with 2 levels (square and rectangular planting), and planting density as

sub-sub factor with 3 levels (160000, 250000 and 444000 pl ha-1). Results showed that by drought stress,

characteristics such as; the plant height, the biological yield of each hill, biological yield, the grain yield of each

hill, grain yield and harvest index, were significantly decreased. With changing square planting to non-square,

some characteristics such as; the plant height, the biological yield of each hill, biological yield, the grain yield of

each hill and grain yield were significantly increased. Results showed that by increasing the planting density,

some characteristics such as; the biological yield of each hill, the grain yield of each hill and harvest index were

significantly decreased. While, some characteristics such as; biological yield and grain yield significantly were

increased.

* Corresponding Author: Ali Sabeti [email protected]

International Journal of Biosciences | IJB |

ISSN: 2220-6655 (Print) 2222-5234 (Online)

http://www.innspub.net

Vol. 5, No. 3, p. 15-24, 2014

http://dx.doi.org/10.12692/ijb/5.3.1-8

mailto:[email protected]

http://www/

16 Sabeti et al.


Introduction

More than 90 percent of rice production in the world

is produced in Asia. This product covers one-third of

the world’s cereals and provides 25 to 60 percent

calories of 2.7 million persons in the world (Tao et al.,

2006). About 75 percent of the world’s rice is

produced from low plains which typically are irrigated

by running water. This method increases the real

consuming water rate (Dawe, 2005).

In drought stress environment, some of plant uses

drought escape mechanism and therefore, reduces

vegetative and reproductive stages (Mohammadi et

al., 2006; Sabeti, 2011). Drought stress can influence

on the procedure of cell expansion via physical and

metabolic changes. For instance, a change in the slope

of water potential can directly influence the cell’s

expansion (Kramer and Boyer, 1995). Along with the

increasing of humidity stress, plant height decreases

(Neilson and Nelson, 1998). The reduction of

accessible soil humidity causes the reduction of

biological yield per hill (Mohammad Zadeh et al.,

2010). By drought stress increasing, there is a

significant reduction in grain yield of each hill

(Human et al., 1998). The periodical stresses in some

rice physiological levels cause an increasing

comparing normal Irrigation level of irrigation;

however by drought stress increasing, the grain yield

is reduced (Kumar et al., 2006; Yang et al., 2003). By

drought stress increasing, there is reduction in

harvest index (Pirdashti et al., 2004).

In rectangular planting, the size and the volume of the

plant are increased which have the greatest influence

on grain yield; it means that in this planting geometry

weight, volume and then grain yield are increased

(Morshed Alam et al., 2002). With the change of

planting geometry from square to non-square, the

plant height increases (Sabeti and JafarZadeh

Kenarsari, 2006).

By increasing the density, the plant height is

increased (Coale and Jones, 1994; Sabeti, 2011). As

density increases, because of the reduction of

vegetative growth, the collection of assimilates is

reduced in each hill and causes the reduction of

biological yield per hill (Sabeti and JafarZadeh

Kenarsari, 2006). By increasing the density, the grain

yield is increased (Hamidul Islam and Altaf hossain,

2002; Sabeti and JafarZadeh Kenarsari, 2006; Zeng,

and Shannon. 2000). By increasing the distance or by

the reduction of planting density in rice, yield of each

hill is increased (Baloch et al, 2002; Sabeti and

JafarZadeh Kenarsari, 2006). As the density of

planting increases, biological yield increases in a

higher manner comparing grain yield and

consequently biological yield increases and harvest

index decreases (Mobser et al., 2009).

Rice is regarded as a drought-sensitive crop and the

drought stress restricting its cultivation. There are

very limited data on the simultaneous effects of

drought stress, planting density and geometry on rice

production in Iran. The aim of this study was to

determine the effects of drought stress, planting

density and geometry on rice production.

Materials and methods

Site climate and geographical situation

This research has been done during two years (2010-

2011) in Khoram Abad (west of Iran) with the

geographical latitude of 33°29' of North latitude and

48°10' of East longitude and in a height of 1091 m

above the sea level. According to 10 years average, the

annual raining is 448.2 mm, the average of

temperature is 17.2°C, the annual rate of vaporing is

1747.2 mm, and the highest wind speed is 19 m/s.

According to official weather reports, this region in

base on Domarten index could be considered as a

semi cold-dry area. The soil physical and chemical

characteristics are shown in Table 1.

Experimental layout

A split-split plots design was done based as

randomized complete block with 4 replications in

2010 and 2011. The factors were drought stress,

planting density and geometry which were arranged

as the follows: drought stress, as main factor with 3

levels as a) normal irrigation, b) retaining irrigation

the plant height of 20-30 cm, and c) 7 days interval

17 Sabeti et al.


between two successive irrigation in vegetative and

reproductive stages), planting geometry as sub factor

with 2 levels (square and rectangular planting), and

planting density as sub-sub factor with

levels(160000, 250000, 444000 pl ha-1). The

combinations of the two latter factors as distance

between hills (cm) are shown in Table 2.

Operation and sampling

The field land was ploughed at the beginning of

autumn for the first time, and after winter it was

ploughed for the second time, and the last time before

planting. The distances between main and sub plots

were determined by borders of 150 and 30 cm. Then

streams were drawn in an exact distance from each

other. The seeds of cultivar Domsyah were sown in

22, April 2010 and 21, April 2011. All of farming

operations, for example: weeds control, fertilizing,

irrigation and fighting with pests and diseases at

growing season were performed. At maturity, plants

were harvested and data were collected for plant

height, biological yield per hill, biological yield, yield

of each hill, grain yield and harvest index were

recorded. The data were subjected to the analysis of

variance using the SAS software. Means comparisons

were made using DMRT method.

Results and discussion

The results of analysis of variance (Table 3) showed a

significant effect of drought stress for all of traits in

both years. The simple effect of Geometry effect was

significant for all of traits in 2011 except harvest

index. The simple effect of density was significant for

biological yield per hill (in 2011), biological yield (in

both years), yield of each hill (in both years), grain

yield (in both years) and harvest index (in 2010).

Table 1. The physical and chemical characteristics of soil of the field.

Characteristics Unit Values

Soil depth CM 0-30

PH - 7.93

Ec ds/m 0.73

Cac % 12.9

B pmm 1.5

Cu pmm 5.6

Zn pmm 0.36

MN pmm 22.4

Fe Pmm 60

K pmm 260

P pmm 19.4

Co % 1.77

N % 0.16

soil texture clay

The two way interaction effect of drought by geometry

was significant for number of grains per spikelet,

number of grains per spike and harvest index and the

two ways interaction effect of density× fertilizer

amount was significant for number of spikes per hill

number of spikes per m2, yield of each hill and grain

yield. The two way interaction effect of fertilizer

splitting× fertilizer amount was significant for

number of spikelets per spike and number of grains

per spike. Finally the three way interaction effect of

density by fertilizer, splitting by fertilizer Amount for

number of spikelets per spike and number of grains

per spikelet (Table 3).

Plant Height

The results from the variance analysis showed

significant effects of drought stress (in 2010 and

2011), planting geometry (in 2011). The drought by

18 Sabeti et al.


geometry interaction effect (in 2011), and geometry

by planting density (in 2010) were also significant

(Table 3).

The higher plant height was obtained in normal

irrigation (Table 4). The comparison between

interaction effects (Table 5) in 2010 showed that

normal Irrigation with non-square planting and non-

square planting with the density of 444000 hills ha-1

cause respectively 9.94 and 5.31 percent increasing in

the plant height. The comparison between interaction

effects (Table 5) in 2011 showed that normal

Irrigation level of irrigation with non-square planting

causes 12.88 percent increasing in the plant height.

These results are corresponding with Neilson and

Nelson (1998). On the other hand, as it shown in the

characteristics of tillers per hill in this experiment, as

draught stress in vegetative treatment increases, the

number of tillers increases. Therefore, more light the

plant receives in its canopy and the more oxin

consumption and then its height increases.

Table 2. Combinations of levels of planting geometry and density (cm).

Planting Density (pl ha-1) Planting Geometry

Rectangular Square

444000 10 x 20 15 x 15

250000 10 x 40 20 x 20

160000 10 x 62 25 x 25

The difference between the height of plant in vegetative

and reproductive stress treatments was not significant

and this is because of the reason that in reproductive

stage stress first growing was in normal irrigation but at

head emergences, the height of plant increases, suddenly

faces stress and it is simultaneous with a very sensitive

level of reproductive stage in which it shocks

reproductive growth and causes the plant height

reduction as the same as stress in vegetative stage.

However, in vegetative stage, draught stress was evolved

with the plant at the beginning growth and this can leads

to an adaptation of plant to the stress which is not

expected in reproductive stress treatment.

Table 3. Variance analysis of the experiment characteristics.

Source df Plant height Biological yield per

hill

Biological yield Yield of each hill Grain yield Harvest index

2010 2011 2010 2011 2010 2011 2010 2011 2010 2011 2010 2011

replication 3 231. 4 * 130.09 2568.3 ** 684.0 178.67 **

17.43 146.20 **

125.49 8.82 ** 14.53 19.38 * 29.20

Drought 2 707.4 ** 1033.7 * 1812.5 ** 4811.5 * 35.75 ** 671.37 **

1059.7 **

2095.2 **

58.28 **

184.4 ** 446.51 **

112.8 *

Error1 6 31.56 126.36 16.72 617.52 3.85 35.01 8.61 100.84 0.23 12.08 3.39 21.04

Geometry 1 0.51 314.75 ** 26.41 12783.4 ** 46.08 951.86 **

127.71 984.27 **

10.16 43.74 ** 0.31 25.95

Drought×geometry 2 55.42 438.1** 4.14 526.61 3.53 35.53 7.27 467.81 * 0.91 48.45 ** 9.87 84.45*

Error2 9 15.18 30.66 275.4 247.78 16.42 25.23 32.60 90.06 2.56 4.14 10.36 12.57

Density 2 22.86 23.92 127.37 1878.56 ** 2122.7 **

3173.1 **

98.91 * 2227.0 **

90.81 **

318.0 ** 565.3 ** 497.47

Drought×Density 4 5.92 63.32 24.62 831.56 * 7.17 97.40 ** 10.04 187.52 0.30 29.66 ** 6.97 171.16

geometry×Density 2 111.4** 60.05 364.71 789.78 36.75 15.24 52.79 211.38 1.84 12.59 20.64 26.01

Drought×geometry×Density 4 13.05 85.46 * 5.23 712.18 3.80 64.79 ** 8.02 336.64 **

0.78 37.13 ** 8.09 56.82

Error3 36 14.92 30.74 179.80 324.20 25.10 18.00 26.29 91.52 4.22 6.19 8.31 16.62

CV% 3.88 4.10 18.76 17.06 23.87 14.41 25.15 19.68 33.14 19.14 6.78 9.41

* and ** significant at 5% and 1% probability levels, respectively.

As the geometry of planting was changed from non-

square to square, the height of plant increases and this is

because of the reason that in non-square geometry of

planting the number of tillers increases significantly and

shadowing of these tillers causes the reduction of oxin

consumption and then the increasing of plant height.

19 Sabeti et al.


This result is corresponding with results of (Sabeti,

2011).

As the planting density increases, the height of plant

increases because in high density to gain more light the

challenge increases and this is the reason of increasing of

the inter node distances. The mechanism is in a way that

in high densities the light gained is reduced because of

the number of hills and this causes a reduction in oxin

consumption and therefore the inter node distances

increases and the height increases; however in low

densities, because of high range of light in canopy, the

oxin consumption is increased and the height does not

increase. These results are corresponding with results

(Coale and Jones, 1994; sabeti, 2011).

Table 4. Means comparisons of simple effects.

Levels of factors Plant height Biological yield per

hill

Biological yield Yield ofeach hill Grain yield Harvest index

2010 2011 2010 2011 2010 2011 2010 2011 2010 2011 2010 2011

Drought stress

No-stress 105.72 a 142.89 a 81.46 a 121.87 a 22.39 a 35.54 a 28.04 a 59.29 a 7.99 a 16.19 a 47.17 a 45.27 a

Vegetative stress 96.14 b 130.72 b 67.13 b 97.27 b 20.40 b 26.85 b 16.16 b 41.95 b 5.30 b 11.48 b 41.58 b 43.59 ab

Reproductive stress 96.49 b 132.54 b 65.78 b 97.41 b 20.18 b 25.97 b 16.95 b 44.58 b 5.30 b 11.31 b 38.68 c 40.97 b

Planting geometry

Square 99.37 a 133.29 b 72.07 a 92.19 b 20.19 a 25.81 b 19.05 a 44.91 b 5.82 a 12.21 b 42.54 a 42.68 a

Rectangular 99.53 a 137.47 a 70.85 a 118.84 a 21.79 a 33.09 a 21.71 a 52.30 a 6.57 a 13.77 a 42.41 a 43.88 a

Planting density

444000 hills per

hectare

99.78 a 136.53 a 69.43 a 96.22 b 30.72 a 42.22 a 18.12 b 37.49 b 8.18 a 16.30 a 37.20 c 38.17 b

250000 hills per

hectare

100.22 a 134.79 a 70.98 a 106.51 ab 20.29 b 26.22 b 22.04 a 53.88 a 6.12 b 13.58 b 43.49 b 44.75 a

160000 hills per

hectare

99.53 a 134.82 a 73.96 a 113.82 a 11.95 c 19.91 c 21.00 a 54.45 a 4.29 c 9.09 c 46.74 a 46.91 a

Means in each column and for each treatment followed by at least on similar letter are not significantly different

at 5% probability level using Duncan Multiple Range Test.

The interaction effect of planting geometry and

density in 2010 was significant. In square geometry,

the distributions of stems in the field were regular

and this reduces the challenge between them from

quantity point of view. Therefore, the negative effects

of high challenge of hills in high densities were

increased with non-square geometry and the highest

range was in the combination of both which was

related to oxin consumption is increased inter node

distances and the plant height.

Biological Yield per Hill

The results from the variance analysis showed

significant effects of drought stress (in 2010 and

2011), planting geometry (in 2011), planting density

(in 2011) and drought by density interaction in 2011

(Table 3).

The comparison between simple effects (Table 4)

showed that water stress in the vegetative and

reproductive stages comparing to control, cause 17.59

and 19.25 percent reduction in biological yield per hill

in 2010. The non-square planting comparing the

square one causes 28.91 percent increasing in

biological yield per hill in 2011. The comparison

between interaction effects of normal irrigation by

density of 250000 hills ha-1 causes 35.21 percent

increasing in the biological yield per hill in 2011

(Table 5).

Draught stress causes the biological yield reduction.

Because of the fact that biological yield per hill is

consisted of the dry weight of hill and the dry weight

of straw, the reduction of this yield leads to the

reduction of biological one. According the results of

Mohammad Zadeh et al (2010) drought stress causes

20 Sabeti et al.


the reduction in biological yield per hill.

As the geometry of square was changed to non-

square, biological yield per hill increases. The

increasing of dry weight of head per hill and straw per

hill reduce biological yield per hill in planting

geometry. As density increases, biological yield

decreases. This is because of the reason that in high

density because of inner and outside challenge and

environmental limitations and conditions, the speed

of vegetative growth was reduced and therefore

biomass canopy was low for each hill. According the

results of Sabeti and Jafarzadeh Kenarsari (2006)

drought stress causes the reduction in biological yield

per hill, moreover, the dry weight of straw and head

pre hill is reduced. Therefore, the biological yield is

reduced.

Table 5. Means comparisons of two way s interaction effects.

Drought stress2011 Planting geometry Yield of each hill Plant hight Grain yield Harvest index

No-stress Square 60.69 a 143.75 a 17.02 a 44.16 a

No-stress Rectangular 57.89 ab 142.02 a 15.38 ab 45.68 a

Vegetative stress Square 35.64 d 123.73 c 10.06 cd 44.87 a

Vegetative stress Rectangular 48.26 bc 137.71 ab 12.57 bc 43.04 ab

Reproductive stress Square 38.40 cd 132.39 b 9.58 d 38.21 b

Reproductive stress Rectangular 50.76 ab 132.68 b 13.39 b 43.74 ab

Table 5 Continued

Drought stress 2011 Planting density Biological

Yield per hill

Biological

yield

Grain

yield

Harvest

index

No-stress 444000 hills ha-1 122.14 ab 52.53 a 21.38 a 40.06 b

No-stress 250000 hills ha-1 124.58 a 30.63 cd 17.01 b 44.71 ab

No-stress 160000 hills ha-1 118.88 ab 23.44 de 10.21 de 48.43 a

Vegetative stress 444000 hills ha-1 85.81 c 38.97 b 14.48 bc 43.97 ab

Vegetative stress 250000 hills ha-1 100.04 abc 24.30 de 11.91 cd 44.25 ab

Vegetative stress 160000 hills ha-1 105.97 abc 17.27 e 7.55 e 46.02 a

Reproductive stress 444000 hills ha-1 80.72 c 35.15 bc 13.07 cd 30.22 c

Reproductive stress 250000 hills ha-1 94.89 bc 23.72 de 11.85 cd 44.27 ab

Reproductive stress 160000 hills ha-1 116.61 ab 19.03 e 9.54 de 47.62 a



Table 5 Continued

Planting geometry Planting density Plant height 010

Square 444000 hills ha-1 97.23 b

Square 250000 hills ha-1 101.05 ab

Square 160000 hills ha-1 99.81 ab

Rectangular 444000 hills ha-1 102.32 a

Rectangular 250000 hills ha-1 99.39 ab

Rectangular 160000 hills ha-1 96.89 b



Biological Yield

The results of analysis of variance showed significant

effect of drought stress (in 2010 and 2011), planting

geometry (in 2011) and planting density (in 2010 and

2011). The drought stress by geometry interaction (in

2011) and drought stress with planting density (in

2011) were also significant (Table 3).


showed that water stress in the vegetative and

21 Sabeti et al.


reproductive stages comparing the control, cause 8.89

and 9.87 percent reduction in biological yield in 2010.

The non-square planting comparing the square one

causes 28.21 percent increasing in biological yield in

2011. The density of 250000 and 444000 hills ha-1

comparing the density of 160000 hills ha-1 cause

69.79 and 157.07 percent increasing in the biological

yield in 2010. The comparison between interaction

effects (Table 5) in 2011 showed that normal

Irrigation with the density of 444000 hills ha-1 cause

67.12 percent increasing in the biological yield.

With a change in geometry of planting from square to

non-square, biological yield increases because in non-

square geometry, the increasing of straw and head

weight per hill causes this increasing. Biological yield

increases along with density and because of past

results we can say that the effect of density on the

number of hills per surface unit is higher than its

negative effect on biological yield per hill. Therefore,

as density increases, biological yield also increases.

According the results of Sabeti and JafarZadeh

Kenarsari (2006) and Mobser et al (2009) drought

stress causes the reduction in biological yield.

The Yield of Each Hill



geometry (in 2011), planting density (in 2010 and in

2011) and drought stress by geometry planting

interaction in 2011 (Table 3).


showed that water stress in vegetative and

reproductive stages comparing the control, caused

42.37 and 39.55 percent yield of each hill in 2010 and

29.25 and 24.81 percent in 2011.The non-square

planting comparing the square one causes 16.46

percent increasing in yield of each hill in 2011. The

density of 250000 and 444000 hills ha-1 comparing

the density of 160000 hills ha-1 cause 4.95 and 13.71

percent reduction yield of each hill in 2010 and also

1.05 and 31.15 percent reduction in 2011, respectively.

While the comparison between interactions effects

(Table 5) in 2010 showed that normal Irrigation with

non-square planting increases the yield of each hill to

38.43 percent.

Drought stress cause the reduction yield of each hill

and this is because of the reason that in drought stress

the lengths of vegetative and reproductive stages are

changed and the time for both of them, especially

reproductive one, is reduced. These results are

corresponding with result of Mohammadi et al (2006)

and sabeti and Jafarzadeh Kenarsari (2006). The

drought stress in vegetative growth decreases yield of

each hill because it can reduce the number of fertile

tillers per hill, the number of grains per head, and the

thousand grains weight in this experiment; and

therefore, these factors are to decrease the yield of each

hill. The drought stress in reproductive stage, because

of the reduction of the factors mentioned, also causes

the reduction in yield of each hill. According the results

of Human et al. (1998) drought stress causes the

reduction in yield of each hill.

The non-square planting increases the yield of each

hill, because in this method, there are good condition

for better growing and this leads to better yield of

each hill. On the other hand, the increasing number of

fertile tillers per hill causes the better yield of each

hill.

By increasing the planting density, the yield of each

hill is reduced, because in high density the distance

between hills is reduced and hence, the needed

sources (such as light, water, nutritional materials,

and space) are reduced for each hill and therefore

reduces its grain yield. These results are

corresponding with results of Sabeti and Jafarzadeh

kenarsari (2006) and Baloch et al (2002).

The Grain yield


effects of drought stress (in 2010 and 2011), planting

geometry (in 2011), planting density (in 2010 and

2011), interaction effect of drought stress by geometry

planting (in 2011), and the drought stress ny planting

density in 2011 (Table 3).

22 Sabeti et al.



showed that water stress in the stage of vegetative and

reproductive stages comparing the control, cause

33.67 and 33.67 percent reduction in grain yield in

2010 and 29.09 and 30.14 percent reduction in 2011.

The non-square planting comparing the square

causes 12.78 percent increasing in grain yield in 2011.

The density of 250000 and 444000 hills ha-1

comparing the density of 160000 hills ha-1 cause

42.66 and 90.68 percent increase in grain yield in

2010 and 49.39 and 79.32 percent increase in 2011.

While the comparison between interaction effects

(Table 5) in 2010 showed that normal Irrigation with

non-square planting and normal Irrigation with the

density of 444000 hills ha-1 increases the grain yield

to 37.71 and 64.69 percent, respectively.

The drought stress decreases the grain yield because

it can reduce the length of vegetative stage and

production of assimilates. Therefore, the assimilation

is reduced and the reduction some of yield

components such as the number of fertile tillers per

hill, the number of fertile heads per square meter, the

number of grains per head and the thousand grains

weight reduce grain yield. Moreover, drought stress in

reproductive stage reduces the period’s length. These

results are corresponding with result of Sabeti and

Jafarzadeh kenarsari (2006). Because the drought

stress has negative effect on assimilation, therefore, it

seems that the reduction in reproductive growth

length and the assimilation decreases the yield

components. According to Yang et al 2003 and

Kumar et al (2006) drought stress causes the

reduction in grain yield.

The non-square planting increases the grain yield,

because in this method, there are good condition for

better growing and this leads to better grain yield. On

the other hand, the increasing number of fertile tillers

per hill, the number of fertile heads per square meter,

and grain yield of each hill cause the better grain

yield. According the results of Alam et al (1992) and

Morshed Alam et al (2002) non-square planting

cause increase in the grain yield.

By increasing the planting density, the grain yield was

increased. According to the previous results (the

number of hills and the yield of each hills), it can be

deduced that the positive effect of the high density on

the number of hills and then the yield, is more than

its negative effect on the reduction of hill’s grain

yield; therefore, by high density, the grain yield is

increased. These results are corresponding with

results of Sabeti and Jafarzadeh kenarsari (2006) and

Hamidul Islam and Altaf hossain (2002).

It is obvious that the high number of some yield

components such as the number of fertile heads per

square meter cause the grain yield increasing.

Harvest Index

The results of variance analysis showed significant


density (in 2010 and 2011), drought stress with

planting geometry interaction effect (in 2011) and

drought stress by planting density in 2011 (Table 3).

The comparison between simple effects (Table 4) in

2010 showed that water stress in the vegetative and

reproductive stages comparing the control, cause

11.52 and 18.00 percent reduction in harvest index.

The density of 250000 and 444000 hills ha-1

comparing the density of 160000 hills ha-1 cause 6.59

and 21.41 percent decreasing in the harvest index. The

comparison between interaction effects (Table 5) in

2011 showed that normal Irrigation level of irrigation

with non-square planting and normal Irrigation level

of irrigation with the density of 160000 hills ha-1

cause 16.35 and 37.60 percent increasing in the

harvest index.

Draught stress causes the reduction of harvest index.

This trait is a fraction that grain yield is placed on its

numerator and biological yield is placed on its

denominator. By studying grain yield and biological

one, it was seen that in non-stress treatment there is

an authority in two characteristics. Therefore, stress

causes reduction in both numbers of harvest index

fractions, but according to the results it can be said

that the reduction from draught stress has more

negative effect on grain yield and this causes the

23 Sabeti et al.


reduction of harvest index fraction.

The lowest amount of harvest index was obtained in

the reproductive stage. Therefore, stress in

reproductive stage causes more reduction in grain

yield comparing vegetative stage. Nevertheless, it

seems that condition in vegetative stage stress is in a

way that the higher index is expected comparing

control treatment, because there is a condition for

denominator to be the smallest and also for the

numerator to be the highest. But it seems that

because of the reason that the leaves in vegetative

stage are supportive of grains to be filled in

reproductive stage, and also because of the reason

that in stress treatment in vegetative stage there is no

availability for photosynthetic machine, the harvest

index in non-stress stage is in its highest amount.

These results are corresponding with results of

PirDashti et al (2004). As density increases, harvest

index reduces because of high reduction of assimilate

to grain. Because of the reason that between the

vegetative and reproductive organs to receive

photosynthetic materials, there exists a challenge, by

increasing the density, this challenge also increases

and reproductive sinks are created posterior than

vegetative sinks. Usually, negative effects of challenge

firstly influences economical (reproductive) sinks and

may causes infertility of some reproductive organs.

Moreover, because of the reason that the reduction of

numerator and denominator in harvest index fraction

and biological yield follow the same procedure,

consequently harvest index reduces because of

increasing the density. These results are

corresponding with result of Ghorbani and Hartonian

(2011) and Mobser et al (2009).

Opposite effect of stress is significant in geometry of

planting, because in square geometry the coverage of

soil surface emerges faster comparing non-square

planting. Therefore, in non-square geometry it is

more possible to vapor in soil. On the other hand, till

the time that there is no stress, the vapor has no effect

on plant, but when stress is applied and it becomes

far from non-stress level, the negative effect of non-

square geometry leads to lack of water in soil (high

stress).

In non-square geometry of planting, the number of

hills increases and because of the reason that there is

no potentiality for hills to produce grains, therefore,

many of these hills may have no grain or have fewer

shares of grains. On the other hand, in non-stress

level, hills face less limitation for their grain

potentiality and this causes a distance between non-

stress level and two stages of stress simultaneously

and therefore there is a maximum for the non-square

geometry of planting and non-stress level

simultaneity.

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