Quantitative evaluation of wheat against volunteer rye in Iran

RESEARCH PAPER

Quantitative evaluation of wheat against volunteerrye in Iran

ALIREZA ATRI,* MOHAMMAD A. BAGHESTANI and MAHBOOBEH PARTOVIWeed Research Department, Plant Protection Research Institute, Tehran, Iran

Rye infestations have increased in frequency and severity in the wheat fields of Iran and havecaused yield reductions in wheat production. In order to study the competition effects ofwheat against rye, an experiment was conducted at the research centers of Karaj andVaramin,Iran, during 2001 and 2002.The experimental design was a randomized complete block with24 treatments and four replications.The treatments included pure stands of wheat at densitiesof 350, 450, 550, and 650 plants m-2 and volunteer rye densities of 10, 30, 50, and 70 plants m-2,and mixed stands of wheat and rye at complete factorial densities.The results indicated that ryewas a superior competitor compared to wheat.The biological and economic yields of wheatwere mainly affected by interspecific competition in the Karaj region.This was also true duringthe first year in theVaramin region but, in the second year, the biological and economic yieldsof wheat were equally affected by interspecific and intraspecific competition because ofincreasing precipitation. The evaluation of competitive ability, using regression coefficients,showed that in Karaj, the effect of one rye plant on wheat was approximately equivalent tothree and two plants of wheat in reducing the grain yield of wheat in the first and second years,respectively, while in Varamin, it was equivalent to three and 1.2 plants of wheat, respectively.In other words, each 0.36 and 0.51 rye plant in Karaj and each 0.36 and 0.84 rye plant inVaramin had the same impact on the reciprocal wheat grain yield as did one wheat plant in thefirst and second years, respectively.

Keywords: competition, quantitative evaluation, reciprocal yield, rye, wheat.

INTRODUCTION

A recent survey of the major weeds in wheat indicatedthat rye (Secale cereale L.) is one of the most common andtroublesome weeds in north-western and central Iran.The hectarage of rye infested with winter wheat isincreasing in western and eastern Iran. It competes withwheat for nutrients, water, and light and seems to bemore efficient than wheat.The presence of rye in wheatgrain might result in a loss of wheat quality.There is noofficial report concerning the yield loss of wheat due tothe presence of this weed in Iran. So far, there is noeffective and/or economical herbicide that controls ryeselectively in winter wheat.

Rye is a cereal grain grown for human consumption, aswell as for forage and grain for livestock (Pester et al.2000). Its plasticity of growth,high reproductive capacity,and low moisture requirement make rye particularly wellsuited as a cover crop planted on roadsides, waterways,and poorly structured soils to prevent soil erosion (Pesteret al. 2000). In addition, rye has a similar life cycle towinter wheat and is well-adapted to the winter wheat–fallow system. These characteristics are responsible forthe persistence of this weed as a noxious weed in winterwheat. It is thought that our current rye problems inwinter wheat originated when rye plants used for theseother purposes escaped into cultivated fields. Since then,the rye plants with the most weedy characteristics (e.g.longer seed dormancy) have thrived in continuouswinter wheat and winter wheat–fallow rotations (Lyonet al. 2004). Rye causes problems because it typicallymatures and shatters before wheat harvest. In the USA, itwas reported that feral rye populations of 18 plants persquare foot reduced the winter wheat yield by 33%

*Correspondence to:Alireza Atri,Weed Research Department, PlantProtection Research Institute, P.O. Box 19395-1454,Tehran, Iran.Email: [email protected]

Received 24 June 2007; accepted 17 December 2007

Weed Biology and Management 8, 191–200 (2008)

© 2008 The AuthorsJournal compilation © 2008 Weed Science Society of Japan

doi:10.1111/j.1445-6664.2008.00295.x

mailto:[email protected]

when removed in February and by 69% when allowed toremain until harvest in July (Lyon et al. 2004). In north-eastern Colorado, winter wheat yields were reduced by14% with feral rye populations as low as five plants persquare foot (Lyon et al. 2004).A single plant of this weedproduces 500–800 seeds; thus, even a low population ofthis weed in the crop dramatically increases the soil seedbank and causes a severe yield loss in wheat fields(Anderson 2004). Feral rye reduced the wheat yield byas much as 92% and represented �73% contaminationin harvested wheat (Stump & Westra 2000). Recentresearch on the longevity of rye seeds in the soil found<20% of feral rye seeds were still alive 1 year after depo-sition into the soil, with <5% of seeds being viable after2 years (Lyon et al. 2004).

Preventative methods are a critical part of an integratedweed management control system for feral rye. Elimi-nating the potential seed sources for rye establishment isa top priority. Planting clean seeds, destroying any feralrye before it produces seeds, and thoroughly cleaningcombines before moving between fields can eliminatethe seed sources. Feral rye is best controlled in winterwheat rotations that include late spring-planted crops,such as corn, grain sorghum, sunflower, or proso millet(Lyon et al. 2004). If a crop rotation is planned with latespring-planted crops following winter wheat, feral ryeusually will not be a problem unless it is not controlledprior to planting the late spring-planted crop and/orduring the following fallow period. With late spring-planted crops, tillage and/or herbicides can be used tocontrol feral rye before planting. Manual weeding is acommon practise for rye control in winter wheat in Iran.Cultural practises, such as an increased planting density,delayed planting date, and nitrogen placement within thesoil profile have been used to reduce competitive effectson the crop (Pester et al. 2000).Although other research-ers have identified rye as a serious weed problem inwinter wheat, there is some limited information con-cerning rye competition with winter wheat and its effecton wheat production economics (Pester et al. 2000).Theobjective of this paper is to evaluate and quantify thecompetition between rye and winter wheat.

MATERIALS AND METHODS

The study was conducted atVaramin and Karaj ResearchStations during 2001 and 2002.The soil was sandy clayloam with a pH of 6.5 and 0.5% organic matter. Theexperimental design was a randomized complete blockdesign with four replications. The interaction betweenwheat and rye was assessed using a bivariate factorialdesign (Snaydon 1991). The treatments included pure

stands of wheat (cv. Mahdavi; Ministry of Agriculture,Karaj, Iran) at densities of 350, 450, 550, and650 plant m-2 and volunteer rye densities of 10, 30, 50,and 70 plant m-2 and all combinations of densitiesbetween the two competing plants consisted of 350:10,350:30, 350:50, 350:70, 450:10, 450:30, 450:50, 450:70,550:10, 550:30, 550:50, 550:70, 650:10, 650:30, 650:50,and 650:70 (wheat : rye densities m-2).All of the weeds,except rye, were controlled by manual weeding. Thetarget rye densities were attained by manual seedingusing the weight of 1000 grains and the percentage ofgermination and vitality of the seeds.The rye seed wasobtained from naturally occurring weedy populations inwinter wheat fields. The plots consisted of four rows,4.2 m long and 60 cm apart, in both years of the experi-ment. The plot width encompassed four 60 cm wideraised beds separated by furrows.The harvesting area wasconfined to the middle of each plot and a 30 cm bufferwas not harvested at each end. There were two borderrows on each side of the plots.The data were collectedfrom the center of each plot. Furrow irrigation wassupplied throughout the growing season between thebeds on a schedule adequate to provide normal cropgrowth.All fertilizer treatments were broadcast when thefield was mowed, in accordance with soil test recom-mendations for grain yields of 6000 kg ha-1.The winterwheat grain yields were determined by manually har-vesting all the plants within a 2 m2 quadrat.The biomassand grain data were analyzed using the reciprocal yieldmodel (Wright 1981; Spitters 1983) of the form:

W a b N b Nw w ww w wr r− = + +1

0 (1)

and

W b N b Nr r rr r rw w− = + +1

0a , (2)

where Ww-1 and Wr

-1 are the reciprocal of the averageyield per plant yields (g plant-1) for wheat and rye,respectively, and Nw and Nr are the density of wheat andrye per unit area, respectively.The intercepts, aw0 and ar0,estimate the reciprocal of the virtual maximum yield ofisolated individual plants for wheat and rye, respectively.The parameters, bww and brr, measure the intraspecificcompetition between the plants, while the interspecificcompetition is estimated by bwr and brw.The parameters’values can be used to drive the indices for the relativecompetitive ability of the weeds by dividing the intraspe-cific competition by the interspecific competition (bww/bwr). If the ratio exceeds unity, it means that theintraspecific competition between the plants is morethan the interspecific competition.

192 A.Atri et al.


Tab

le1.

Res

ults

ofth

eec

onom

ican

dbi

olog

ical

indi

vidu

alpl

ant

yiel

dof

whe

at,u

sing

the

reci

proc

alyi

eld

mod

el†

inth

eVa

ram

inre

gion

Dep

ende

ntva

riab

le(w

-1)

Inve

rse

max

imum

plan

tw

eigh

tin

no-c

ompe

titio

nsit

uatio

n(a

10)

Intr

aspe

cific

com

petit

ion

(b11

)(m

2 /g.

n)

Inte

rspe

cific

com

petit

ion

(b12

)(m

2 /g.

n)

Max

imum

plan

tw

eigh

tin

no-c

ompe

titio

nsit

uatio

n(a

10-1

)

Rel

ativ

eco

mpe

titiv

eab

ility

(b11

/b12

)

1st

year

2nd

year

1st

year

2nd

year

1st

year

2nd

year

1st

year

2nd

year

1st

year

2nd

year

Rec

ipro

cal

indi

vidu

alpl

ant

wei

ght

ofth

eec

onom

icyi

eld

0.06

73‡

(0.0

527)

§0.

3064

**(0

.068

8)0.

0016

0**

(0.0

0001

)0.

0009

**(0

.000

1)0.

0044

*(0

.000

4)0.

0010

§(0

.000

6)14

.86

3.26

0.36

0.9

Rec

ipro

cal

indi

vidu

alpl

ant

wei

ght

ofth

ebi

olog

ical

yiel

d

0.11

81**

(0.0

137)

0.09

77**

(0.0

256)

0.00

060*

*(0

.000

01)

0.00

04**

(0.0

001)

0.00

15**

(0.0

001)

0.00

04§

(0.0

002)

8.47

10.2

40.

401.

0

†W

w-1

=a 1

0+

b 11N

w+

b 12N

r;‡

not

signi

fican

t;§

the

valu

esin

pare

nthe

ses

indi

cate

the

stan

dard

erro

rof

the

mea

n;*

and

**,a

signi

fican

tdi

ffere

nce

at5%

and

1%pr

obab

ility

,res

pect

ivel

y.g.

n,gr

am.n

umbe

r.

Tab

le2.

Res

ults

ofth

eec

onom

ican

dbi

olog

ical

indi

vidu

alpl

ant

yiel

dof

whe

at,u

sing

the

reci

proc

alyi

eld

mod

el†

inth

eK

araj

regi

on

Dep

ende

ntva

riab

le(w

–1)

Inve

rse

max

imum

plan

tw

eigh

tin

no-c

ompe

titio

nsit

uatio

n(a

10)

Intr

aspe

cific

com

petit

ion

(b11

)(m

2 /g.

n)

Inte

rspe

cific

com

petit

ion

(b12

)(m

2 /g.

n)

Max

imum

plan

tw

eigh

tin

no-c

ompe

titio

nsit

uatio

n(a

10–1

)

Rel

ativ

eco

mpe

titiv

eab

ility

(b11

/b12

)

1st

year

2nd

year

1st

year

2nd

year

1st

year

2nd

year

1st

year

2nd

year

1st

year

2nd

year

Rec

ipro

cal

indi

vidu

alpl

ant

wei

ght

ofth

eec

onom

icyi

eld

0.20

47*

-0.2

566§

0.00

31**

0.00

34**

0.00

86**

0.00

67**

4.89

–0.

360.

51(0

.094

2)‡

(0.1

603)

(0.0

002)

(0.0

003)

(0.0

008)

(0.0

013)

Rec

ipro

cal

indi

vidu

alpl

ant

wei

ght

ofth

ebi

olog

ical

yiel

d

0.06

16§

0.05

61§

0.00

14**

0.00

11**

0.00

33**

0.00

19**

16.2

317

.80.

420.

58(0

.034

3)(0

.072

3)(0

.000

1)(0

.000

1)(0

.000

3)(0

.000

6)

†W

w-1

=a 1

0+

b 11N

w+

b 12

Nr;

‡th

eva

lues

inpa

rent

hese

sin

dica

teth

est

anda

rder

ror

ofth

em

ean;

§no

tsig

nific

ant;

*an

d**

,asig

nific

ant

diffe

renc

eat

5%an

d1%

prob

abili

ty,r

espe

ctiv

ely.

g.n,

gram

.num

ber.

Evaluation of wheat against volunteer rye 193


RESULTS AND DISCUSSION

The results indicated that rye was the superior competi-tor each year (Tables 1,2). In the first year in the tworegions, the interspecific coefficient (bwr) was greaterthan the intraspecific coefficient (bww) with respect tothe biomass and grain yield of wheat,while in the secondyear, especially in the Varamin region, rye had a lowercompetition effect compared with the first year becauseof increasing precipitation. Three-dimensional graphs,

related to the first year of the experiment in the tworegions, showed that the slope of the regression planescorresponded to the competition coefficients: rye isgreater than wheat (Figs 1,2).The greater the slope, thelarger the competition coefficient (Panton & Baker1991). In 2002, the slope of the regression planes asso-ciated with the effect of the density of rye on the wheatbiomass and grain yield (Figs 1,2) reflected the dominanteffect of rye: competition was principally interspecific. In2002 in theVaramin region, the effect of the rye densities

Rec

ipro

cal i

ndiv

idua

l pla

nt w

eigh

t of

the

econ

omic

yie

ld (

1g–1

)

Rec

ipro

cal i

ndiv

idua

l pla

nt w

eigh

t of

the

biol

ogic

al y

ield

(1g

–1)

0.25

0.30

0.35

0.40

0.45

0.50

0.55

0.60

0.65

350

400

450

500

550

600650

010

2030

4050

60

0.20

0.22

0.24

0.26

0.28

0.30

0.32

0.34

0.36

0.38

350

400

450

500

550

600650

010

2030

4050

60

0.4

0.6

0.8

1.0

1.2

1.4

1.6

350

400

450

500

550

600650

010

2030

4050

60

Whe

at d

ensit

y (p

m–2 )

Whe

at d

ensit

y (p

m–2 )

Rye density (p m–2)

Whe

at d

ensit

y (p

m–2 )


Whe

at d

ensit

y (p

m–2 )



0.6

0.7

0.8

0.9

1.0

1.1

350

400

450

500

550

600650

010

2030

4050

60

(a) (c)

(b) (d)

Fig. 1. Effect of the wheat and rye densities on the reciprocal individual plant weight of the economic yield (a and c) andthe biological yield (b and d) in the first (a and c) and second (b and d) experimental years in the Varamin region.Therelationships were described by the following regression equations: (a) Ww

-1 = 0.0673 + 0.0016Nw + 0.0044Nr; (b)Ww

-1 = 0.1181 + 0.0006Nw + 0.0015Nr; (c) Ww-1 = 0.3064 + 0.0009Nw + 0.0010Nr; and (d) Ww

-1 = 0.0977 +0.0004Nw + 0.0004Nr.

194 A.Atri et al.


on the wheat biomass and grain yield was less than thefirst year and approximately equal to the wheat densitiesbecause of increasing precipitation.

Linear graphs also can illustrate the effects of rye densi-ties on the wheat biomass and grain yield (Figs 3,4).Thedistance between the lines indicates the competitioneffect of rye on wheat.The further the distance between

the lines, the more interspecific the competition (Atriet al. 2000).The results showed that, in the second year,the distance between the lines is less than in the first year.However, the rye densities had a lower competitioneffect on wheat (Figs 3,4).The distance of the lines fromthe horizontal axis indicates the yield per unit area. Ashorter distance indicates a greater reciprocal per plantweight and more yield per unit area (Atri et al. 2000).

1.0

1.2

1.4

1.6

1.8

2.0

2.2

2.4

2.6

2.8

3.0

350

400

450

500

550

600650

010

2030

4050

60

0.4

0.6

0.8

1.0

1.2

1.4

350

400

450

500

550

600650

010

2030

4050

60

0.8

1.0

1.2

1.4

1.6

1.8

2.0

2.2

2.4

2.6

2.8

350

400

450

500

550

600650

010

2030

4050

600.4

0.5

0.6

0.7

0.8

0.9

1.0

350

400

450

500

550

600650

010

2030

4050

60

(a)(b)

(c) (d)

Whe

at d

ensit

y (p

m–2 )

Whe

at d

ensit

y (p

m–2 )



Whe

at d

ensit

y (p

m–2 )


Whe

at d

ensit

y (p

m–2 )


Rec

ipro

cal i

ndiv

idua

l pla

nt w

eigh

t of

the

econ

omic

yie

ld (

1g–1

)

Rec

ipro

cal i

ndiv

idua

l pla

nt w

eigh

t of

the

biol

ogic

al y

ield

(1g

–1)

Fig. 2. Effect of the wheat and rye densities on the reciprocal individual plant weight of the economic yield (a and c)and the biological yield (b and d) in the first (a and b) and second (c and d) experimental years in the Karaj region.The relationships were described by the following regression equations: (a) Ww

-1 = 0.2047 + 0.0031Nw + 0.0086Nr;(b) Ww

-1 = 0.0616 + 0.0014Nw + 0.0033Nr; (c): Ww-1 = -0.2566 + 0.0034Nw + 0.0067Nr; and (d) Ww

-1 = 0.0561 +0.0011Nw + 0.0019Nr.



0.0

0.5

1.0

1.5

2.0

2.5

3.0

350 650550450

(d)

Rec

ipro

cal i

ndiv

idua

l pla

nt w

eigh

t of t

he e

cono

mic

yie

ld (

1 g–1

)

0.0

0.5

1.0

1.5

2.0

2.5

3.0

350 650550450

(c)

Rec

ipro

cal i

ndiv

idua

l pla

nt w

eigh

t of t

he e

cono

mic

yie

ld (

1 g–1

)

Wheat density (m2) Wheat density (m2)

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

350 650550450

(b)

Rec

ipro

cal i

ndiv

idua

l pla

nt w

eigh

t of t

he e

cono

mic

yie

ld (

1 g–1

)

Wheat density (m2)

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

350 650550450

(a)

Rec

ipro

cal i

ndiv

idua

l pla

nt w

eigh

t of t

he e

cono

mic

yie

ld (

1 g–1

)

Wheat density (m2)

Fig. 3. Reciprocal individual weight of the economic yield of wheat atVaramin (a and b) and Karaj (c and d) in differentdensities of rye in 2000 and 2001, respectively. (�), 0 plants m-2; (�), 10 plants m-2; (�), 30 plants m-2; (�), 50 plants m-2;(�), 70 plants m-2.

196 A.Atri et al.


350

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

650550450

(c)

Rec

ipro

cal i

ndiv

idua

l pla

nt w

eigh

t of t

he b

iolo

gica

l yie

ld (1

g–1

)

Wheat density (m2)

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

350 650550450

(d)

Rec

ipro

cal i

ndiv

idua

l pla

nt w

eigh

t of t

he b

iolo

gica

l yie

ld (1

g–1

)

Wheat density (m2)

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

350 650550450

(b)

Rec

ipro

cal i

ndiv

idua

l pla

nt w

eigh

t of t

he b

iolo

gica

l yie

ld (1

g–1

) Wheat density (m2)

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

350 650550450

(a)R

ecip

roca

l ind

ivid

ual p

lant

wei

ght o

f the

bio

logi

cal y

ield

(1 g

–1)

Wheat density (m2)

Fig. 4. Reciprocal individual weight of the biological yield of wheat atVaramin (a and b) and Karaj (c and d) in differentdensities of rye in 2000 and 2001, respectively. (�), 0 plants m-2; (�), 10 plants m-2; (�), 30 plants m-2; (�), 50 plants m-2;(�), 70 plants m-2.



The intercept predicted the reciprocal of the virtualmaximum yield of isolated individual plants (Spitters1983; Kropff & Lotz 1993).Therefore, a smaller interceptindicates a larger potential maximum yield per plant.Intercept values significantly different from zero wereobtained during 2001 in Karaj for the grain yield onlyand in 2002 inVaramin for the wheat biomass and grainyield (Tables 1,2).

No significant negative intercept was measured during2002 for the wheat grain yield in Karaj (Table 2).A zeroor negative intercept is biologically irrational and canprobably be attributed to random error (Panton & Baker1991). Other researchers have reported insignificantnegative intercepts, which were probably the result ofattempting to estimate values outside the range of den-sities on the regression equation (Rejmanek et al. 1989;Roush et al. 1989; Panton & Baker 1991).The evaluationof competitive ability, using regression coefficients,showed that the effect of one rye plant during 2001 and2002 in Karaj was approximately equivalent to three andtwo wheat plants in reducing the grain yield of wheatand 2.35 and 1.7 wheat plants in reducing the biomassyield of wheat, respectively. This means that each 0.36and 0.51 rye plant had the same impact on the reciprocalwheat grain yield and each 0.42 and 0.58 rye plant hadthe same impact on the reciprocal wheat biomass yield asdid one wheat plant (Table 2). InVaramin, the competi-tive ability of rye for the wheat grain yield during 2001and 2002 was 3.0 and 1.1 wheat plants and, for the wheatbiomass yield, it was 2.5 and 1.0 wheat plant, respectively,indicating that each 0.36 and 0.84 rye plant had the

equivalent effect on the grain yield of wheat and each0.4 and 1.0 rye plant had the equivalent effect on thebiomass yield of wheat as did one wheat plant (Table 1).This difference was related to higher precipitation in2002. Some researchers have reported that rye has ahigher tolerance to drought compared to wheat (Barnes& Putnam 1987), which might be why the competitiveability of rye was greater in the first year than in thesecond year.

In comparing the grain and biomass yields of wheat inthe two regions and years (Tables 1,2), the grain yieldwas reduced more than the biomass yield.The grain yieldis more sensitive to stress than the biological yield.Theyield per unit area was predicted using this model(Figs 5,6). The biomass and grain yield of wheat weremainly affected by the rye density. The yield decreasedwith an increasing rye density, but the rate of yieldreduction was not constant.The percentage of yield lossat the lower densities of rye was more than at the higherdensities. It seems that in lower densities of rye, interspe-cific competition caused severe yield loss, but withincreasing rye densities, the intraspecific competition ofrye became more important.

In view of the above discussion, it is essential to considerfield sanitation as our top priority in order to controlvolunteer rye in winter wheat. That is because rye is asuperior competitor compared to wheat and there is noeffective herbicide that controls rye selectively in wheatfields. It is also necessary to do some research related tothe economic threshold of rye in winter wheat.

(a)E

con

om

ic y

ield

of

wh

ea

t (t

ha

–1)

Wheat density (p m –2)Rye density (p m

–2 )

(b)

Eco

no

mic

yie

ld o

f w

he

at

(t h

a–1)

Wheat density (p m –2)

Rye density (p m–2 )

(c)

Eco

no

mic

yie

ld o

f w

he

at

(t h

a–

1)

Wheat density (p m –2) Rye density (p m–2 )

Fig. 5. Effect of the wheat and rye densities on the economic yield of wheat per unit area atVaramin (a and b) and Karaj(c).

198 A.Atri et al.


ACKNOWLEDGMENTS

The financial support for this survey was provided by thePlant Protection Research Institute, Tehran, Iran. Theauthors thank the internal and external reviewers fortheir helpful comments.

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Fig. 6. Effect of the wheat and rye densities on the biological yield of wheat per unit area atVaramin (a and b) and Karaj(c and d) in the first (a and c) and second (b and d) experimental years.



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Quantitative evaluation of wheat against volunteer rye in Iran

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