Can Peak-LAI be used as an appropriate index to

estimate wheat performance under weed

competition?

Saeid Soufizadeh, Eskandar Zand, Mohammad Ali Baghestani,

Mohammad Bannayan, Reza Deihimfard

Dept. of Agronomy, Faculty of Agriculture, Tarbiat Modares University, Iran.

Middle East

- Has an arid climate in which most of the relatively scant annual precipitation falls from October through April

Iran

- One of the only countries in the world which has the complete four seasons.

- Yearly precipitation averages 25 centimeters or less:

Less than 10 centimeters in the Central Plateau; More than 100 centimeters in the Caspian Coastal Plain

- The most important winter cereal grown in Iran

- Area under cultivation: 6.2 mha

- Annual production: 14.5 mt

- Ranks second after maize in the world cereal output

Wheat:

Introduction

Weeds in wheat crop compete with the crop for nutrients, water, and light as with other crops.

Weeds are more competitive when moisture is limiting and especially under drought situation;

when young wheat does not compete well with weeds.

Weeds are one of the most important factors that reduce the wheat yield in Iran.

Reported wheat yield loss in Iran due to weeds: 30%

So, why control?

- Crop competition

- Prevent economic loss

- Hosts for insects and diseases

Weeds infesting wheat in Iran

Grass weeds

Avena fatua Phalaris minor

Secale cereale

Lolium rigidum

Hordeum spontaneum

Weeds infesting wheat in Iran

Broadleaved weeds

Eruca sativa Sisymbrium officinale

Sinapis arvensis

Cirsium arvense

Galium aparine

Weed management strategies

Identify weed, life cycle, habitat

Integrated weed management

Preventive

Physical

Cultural

Biological

Chemical

Enhancing crop competitiveness is one of the promising approaches

toward IWM and toward decreasing herbicide consumption.

Factors affecting weed competition:

- Timing of emergence

- Growth form

- Weed density

- Duration of competition

- Physiological basis of competition

√

√

Weed competition affecting by growth form:

Root developmentHeightLeaf areaPlant growth rate

Distinct competitive advantage

Rapid growthLonger period of initial growthTallDense canopyGreater leaf area

Our aim:

To asses the competitive ability of the Iranian wheat cultivars released within different eras in response to weeds.

Our research question:

Can Peak-LAI be used as an appropriate and easy-to-measure index to estimate wheat performance under weed competition?

Materials and methods

Site description:

8 field experiments at two locations in 2003-2004.

Locations:

Karaj

Latitude: 35°50’Longitude: 50°01’

Elevation: 1020 maslClimate: Semi-aridAnnual precipitation: 250 mmAnnual long-term temperature: 14°CSoil: Clay loam

Varamin

Latitude: 35°19’Longitude: 51°40’

Elevation: 1320 maslClimate: Semi-aridAnnual precipitation: 240 mmAnnual long-term temperature: 30°CSoil: Sandy loam

Experimental treatments

8 wheat cultivars x 2 weed management strategy (weedy & weed-free)

4 replications

Plot size: 2.4m x 6m

Row spacing: 0.30m

Experimental design: RCBD with factorial arrangement of treatments

Materials and methods

CultivarsYear of releasePlanting density (Grains/m2)

Optimum N (kg/ha)

Tabasi1955250110

Roshan1957250110

Karaj21975325110

Azadi1979325105

Niknejad1995425120

Mahdavi1995375130

Shiraz2000400120

Pishtaz2002400120

Materials and methods

Weed species

(Common name)

Weed species

(Latin name)

Planting density (Plants/m2)

Wild oatAvena fatua120

Common ryeSecale cereale120

FlixweedDescurainia sophia80

RocketEruca sativa80

Materials and methods

Cultural practices

Irrigation: immediately after planting and throughout the growing season (no water deficit symptom occurred).

No need to apply insecticides and fungicides.

All weeds except the target weed species were effectively controlled throughout the growing season.

Planting dates: November 2nd at Karaj. November 6th at Varamin.

Fertilization: Ammonium phosphate 150 kg/ha Urea 100 kg/ha (at planting) Urea 50 kg/ha (at tillering) Urea 50 kg/ha (at heading)

Measurements DAP (Days after planting)

Crop biomass and LAI: (from stem elongation at two-weeks intervals)

Crop yield & biomass: (at physiological maturity)

Weed biomass: (at crop physiological maturity)

R = Grain yield (weedy)

Grain yield (weed-free)

R > 1 : Able to suppress weeds

0.90 < R < 1 : Able to tolerate weeds

Results

Significant differences were observed in the yielding ability of the wheat cultivars in competition

with different weed species.

Results

Wheat - Wild oatCultivarsR (Karaj)R (Varamin)

Tabasi0.68c0.77bc

Roshan1.54a0.95b

Karaj20.92b1.17a

Azadi0.86bc0.77bc

Niknezhad0.96b1.29a

Mahdavi0.75c0.73bc

Shiraz0.85bc0.57c

Pishtaz0.74c1.01ab

Wheat - RyeCultivarsR (Karaj)R (Varamin)

Tabasi-0.66bc

Roshan-0.69b

Karaj2-0.63bc

Azadi-0.54c

Niknezhad-0.74b

Mahdavi-0.68b

Shiraz-0.44c

Pishtaz-0.92a

Results

Results

Wheat - FlixweedCultivarsR (Karaj)R (Varamin)

Tabasi0.94b0.63c

Roshan1.30a1.05b

Karaj20.81c1.61a

Azadi0.65d0.98bc

Niknezhad0.73cd1.55a

Mahdavi0.97b1.00b

Shiraz0.74cd1.18b

Pishtaz0.93b1.10b

Results

Wheat - RocketCultivarsR (Karaj)R (Varamin)

Tabasi0.94b1.11bc

Roshan1.30a1.42b

Karaj20.81c1.48b

Azadi0.65d0.80cd

Niknezhad0.68d1.99a

Mahdavi0.97b0.85c

Shiraz0.74cd0.71d

Pishtaz0.93b1.07bc

Results

Common rye is a stronger competitor of wheat than other weed species.

The suppressive ability of the wheat crop not only depends on the cultivar but also to the weed species.

The wheat cultivars’ response to the weeds differedbetween locations:

Karaj: RoshanVaramin: Niknejad and Karaj2

Results

0

1

2

3

4

5

6

Wild oat(Free)

Wild oat(Infested)

Rye (Free) Rye(Infested)

Rocket(Free)

Rocket(Infested)

Flixweed(Free)

Flixweed(Infested)

K V

Tabasi

0

1

2

3

4

5

6

7

Wild oat(Free)

Wild oat(Infested)

Rye (Free) Rye(Infested)

Rocket(Free)

Rocket(Infested)

Flixweed(Free)

Flixweed(Infested)

K V

Roshan

Peak-LAI

0

1

2

3

4

5

6

7

Wild oat(Free)

Wild oat(Infested)

Rye (Free) Rye(Infested)

Rocket(Free)

Rocket(Infested)

Flixweed(Free)

Flixweed(Infested)

K V

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

Wild oat(Free)

Wild oat(Infested)

Rye (Free) Rye(Infested)

Rocket(Free)

Rocket(Infested)

Flixweed(Free)

Flixweed(Infested)

K V

Results

Azadi Niknejad

Peak-LAI

Results

Karaj2 Mahdavi

0

1

2

3

4

5

6

Wild oat(Free)

Wild oat(Infested)

Rye (Free) Rye(Infested)

Rocket(Free)

Rocket(Infested)

Flixweed(Free)

Flixweed(Infested)

K V

0

1

2

3

4

5

6

7

Wild oat(Free)

Wild oat(Infested)

Rye (Free) Rye(Infested)

Rocket(Free)

Rocket(Infested)

Flixw eed(Free)

Flixw eed(Infested)

K V

Peak-LAI

Results

Shiraz Pishtaz

0

1

2

3

4

5

6

7

Wild oat(Free)

Wild oat(Infested)

Rye (Free) Rye(Infested)

Rocket(Free)

Rocket(Infested)

Flixweed(Free)

Flixweed(Infested)

K V

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

Wild oat(Free)

Wild oat(Infested)

Rye (Free) Rye(Infested)

Rocket(Free)

Rocket(Infested)

Flixweed(Free)

Flixweed(Infested)

K V

Peak-LAI

Results

y = -301.08x + 5690.7

R2 = 0.1087

0

1000

2000

3000

4000

5000

6000

7000

0 1 2 3 4 5 6 7 8

y = 1517.2x + 10426

R2 = 0.2457

0

5000

10000

15000

20000

25000

30000

0 1 2 3 4 5 6 7 8

Grain yield vs. Peak-LAI)Weed-free(

Biomass vs. Peak-LAI)Weed-free(

Results

y = -101.49x + 3970.9

R2 = 0.016

0

1000

2000

3000

4000

5000

6000

7000

0 1 2 3 4 5 6 7

y = 1428.9x + 11597

R2 = 0.2241

0

5000

10000

15000

20000

25000

30000

35000

0 1 2 3 4 5 6 7

Grain yield vs. Peak-LAI)Weedy(

Biomass vs. Peak-LAI)Weedy(

Conclusion

Investing more biomass in leaf under Weed-free condition does not seem a good

strategy to increase the wheat yield.

Peak-LAI could be used successfully as an estimator of the wheat crop under weed

competition along with some other measures ONLY but not alone.

Thank you all for your attention.