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Comparative efficacy of sorghum allelopathic potential for controlling barnyardgrass in rice

Aamer Irshad1 and Zahid Ata Cheema2

1Rice Research Institute, Kala Shah Kaku, Lahore-39018, Pakistan. Tel. no. +92-42-7980368. Fax no. +92-42-7980361.
E. Mail: aamer_irshad@yahoo.com
2
Department of Agronomy, University of Agriculture, Faisalabad – 38040, Pakistan. Tel. no. +92-41-9200161-7 Ext.380. Fax no. +92-41-9200183.E. Mail: - zacheema@pakwatan.com

Abstract

To control weeds by the manipulation of allelopathic properties of plants is a new promising approach to avoid the hazardous use of chemicals. A field experiment was therefore, conducted to develop an environmentally safe method to manage barnyardgrass (Echinochloa crus- galli (L.) Beauv) in rice (Oryza sativa L.) under semi arid conditions of Faisalabad, Pakistan. The treatments consisted of one hand weeding (pulling) 20 days after transplanting, chemical control (Butachlor pre emergence @ 1.2 kg a.i. /ha), sorghum (Sorghum bicolor L.) water extract as one- or two-time foliar spraying 20 and 40 days after transplanting and weedy field as control. Minimum barnyardgrass density was observed with chemical control each year followed by hand weeding. Sorghum water extract significantly reduced barnyardgrass dry mass by 38-41%, while hand weeding and butachlor decreased by 90% and 95% respectively as compared to weedy check. Butachlor increased rice grain yield by 36%, hand weeding by 31% and one-time spraying with water extract of sorghum resulted by 20%, where two-time spraying increased the yield by only 18%, may be due to suppression of rice as well. Simple regression analyses showed that grain yield is negatively correlated (R2, 0.95) with barnyardgrass dry mass. Chemical control gave highest net benefits, while one spray of sorghum extract had highest percentage of marginal rate of return. Hand weeding was effective but uneconomical due to higher cost. This provides a base to use sorghum water extract as natural weed inhibitor in rice.

Media summary

A new environment friendly technique developed to manage the worst and most efficient weed (Barnyardgrass) of rice that will boost yield without contributing to pollution.

Key Words

Basmati-385, weed, allelopathic control, chemical control

Introduction

Barnyardgrass (Echinochloa crus- galli (L.) Beauv) is a world’s worst weed of the rice (Oryza sativa L.) crop. It may decreases yield up to 90% through season long competition with rice (Kwesi et al. 1991).

The reason of the high competitiveness of barnyardgrass is that, it is an efficient plant (C4 metabolism) as compared to rice (C3 metabolism). Moreover, it is morphologically very similar and has the same ecological requirements as of rice. Hence growing in similar conditions it thrives well as compared to rice. It produces huge number of seeds per plant, which ensures its dispersals and reestablishment (Kim and Park 1996).

The direct weed control technologies for rice crop in Pakistan include hand weeding, chemical control with herbicides and allowing the water (3-5 cm) to stand in the rice field for 30-40 days after transplanting (Shad et al. 1986). The later technique is effective but is employed only in the soils where puddling is possible. However, it is impracticable under semiarid conditions of Faisalabad where sufficient water supply is also a problem. Pulling of weeds by hand is the surest way to control weeds but the increasing cost of labors or its scarcity during critical periods is the major reasons that limit its use. In the current circumstances, this technique may supplements other weed control methods. Moreover, due to the morphological resemblance between barnyardgrass and rice, only an expert can distinguish these two plant species. Herbicidal control of rice weeds including barnyardgrass is quite useful but this requires special skill and may give rise to health hazards and cause environmental pollution by contaminating water, soil and air. An alternative to overcome these problems could be the utilization of allelopathy.

The use of allelopathic properties of different plants has been investigated for providing economical and natural weed control. Allelopathic water extracts of sorghum (Sorghum bicolor L.) plant named as “Sorgaab” (SWE) has shown its promise by suppressing weeds up to 40-50% and improving yields of wheat, maize and mungbean crops (Cheema and Khaliq 2000; Cheema et al. 2000). The present experiment was therefore designed to evaluate the possible use of sorghum water extract against barnyardgrass at Faisalabad conditions in comparison with hand weeding and butachlor (a standard herbicide for barnyardgrass control in rice crop).

Materials and methods

A two-year field study (during 1998 and repeated during 1999 with the same treatments to confirm the results) was conducted to assess the efficiency of different weed control methods against the barnyardgrass in transplanted fine rice under semiarid conditions. Experiments were done at the Agronomic research area University of Agriculture, Faisalabad, Punjab, Pakistan. The soil belongs to Lyallpur soil series (aridisol-fine-silty, mixed, hyperthermic Ustalfic, Haplarged in USDA classification and Haplic Yermosols in FAO classification). The experimental soil have pH 7.85 and 7.90 and organic matter 0.70 and 0.71% during both year of study respectively. Different weed control methods included in the study were hand weeding, chemical control and sorghum water extracts (SWE) as one and two foliar sprays. Experiment control was field without weeding. Hand weeding was done 20 days after transplanting. Butachlor (herbicide) was sprayed with in 2-3 days after rice transplanting at the rate of 1.2 kg a.i./ha. Sorghum water extract was sprayed 20 and 40 days after transplanting as one and two foliar sprays. Experiment was laid out in randomized complete block design with 4 replications in plots measuring 2m x 3m. To prepare sorghum water extract, mature sorghum plant herbage was dried, chopped with fodder cutter and soaked in distilled water for 24 hrs. in ratio of 1:10, i.e. 1 kg plant herbage in 10 liters of distilled water. The sorghum extract was obtained by filtering the mixture through sieves (10 and 60 mesh) and used afresh either as such or stored in freezer at -15C for further use. About one month old 1-2 seedlings of fine cv. Basmati-385 were transplanted on well-prepared puddled soil (previously harvested with wheat crop during two years) maintaining 25cm x 25cm hill sparing in the 1st week of July. Recommended dose of fertilizer was applied @120-60-60 kg NPK /ha. Whole of the P and K in the form of single super phosphate and sulphate of potash and half of the nitrogen in the form of urea was applied at the time of transplanting, while remaining half of the nitrogen was applied 30 days after transplanting. Weekly irrigation was given to the rice crop throughout the season till maturity. All other crop production practices were kept normal.

To maintain the sufficient barnyardgrass density, its seeds (previously collected) were broadcasted at the time of transplanting. The other weed floras like jungle rice (Echinochloa colonum L.) and purple nut sedge (Cyperus rotundus L.) were uprooted soon after their emergence. Barnyardgrass density was recorded by randomly selected quadrate measuring 0.5m x 0.5m at three sites in each plot at the harvesting time. Barnyardgrass plants were counted and collected for dry weight (70oC oven dry until constant weight).

Leaf area of rice crop at 30, 50, and 70 days after transplanting was recorded through length-width method (Yoshida et al., 1976) and the leaf area index was determined by LAI = Leaf area per hill/land area per hill (Watson, 1947). The data on final plant height, grain yield, straw yield and harvest index were recorded at final harvest from random samples by adapting standard methods. Combined over year analysis of all the collected data were performed by using the ANOVA on Computer package MSTATC (Anonymous 1986). Duncan’s new multiple range test was used for treatment comparisons. Simple regression analysis was also performed. As in all observations interactive effect of treatments with years (location) was non significant therefore means of the two years were discussed.

The economic analysis was carried out on the basis of variable costs and prevailing market prices of herbicide and crop. Marginal analysis was also carried out as suggested by Byerlee (1988).

Results and discussion

The various weed control practices had significant effect on the barnyardgrass density during both the years of study. Application of butachlor pre emergence @ 1.2 kg a.i. /ha (M3) resulted in the lowest number of weeds (1.62) and was followed by hand pulling treatment (M2) where was 4.62 weeds. Sorghum water extract (SWE) one spray (M4) at 20 days after transplanting (DAT) and sorghum water extract two sprays (M5) at 20 and 40 DAT had no effect on the barnyardgrass density. Pre-emergence application of butachlor appeared the effective control measure in reducing barnyardgrass density, as it suppressed the germination of barnyardgrass. These results are supported by Bhattacharya and Mandal (1988) who stated that butachlor and hand weeding are best methods to reduce the weed density. The non-significant effects of sorghum water extract on barnyardgrass density are contrary to the previous findings, which indicated the reduction in weed density with sorghum water extract spraying (Cheema et al. 2000). The dry matter accumulation reflects the growth behaviour of a weed and gives better indication of weed crop-competition than the weed density. Greater weed dry weight reflects more utilization of soil and environmental resources by the weed at the expense of the crop growth. Data presented in Table 1 revealed that barnyardgrass dry mass was significantly affected by different control methods. The minimum dry mass (36.38 g/m2) was recorded in butachlor treated plots followed by hand weeding. (M2) Foliar spraying with sorghum water extract suppressed the barnyardgrass growth by 38-41%. This supports the previous findings indicating the inhibitory allelopathic effects of sorghum water extract on weeds growth (Cheema et al. 2000). The lower weeds dry-weight in M2 and M3 treatments may be due to the effective and timely control of the barnyardgrass. While the reduced dry weight with two sprays of sorghum water extract was due to its suppressive effect on the vegetative growth of the barnyardgrass. These results are also supported by Janordhan and co-workers (1993) who concluded that effective weed control methods reduce the dry weight of weeds per unit area. A negative correlation was found between grain yield and weed dry mass. The regression lines (Fig 1) indicate a progressive decrease in the grain yield with the successive increase in weed dry mass having a determination coefficient of 0.9472.

All the leaf area indices (LAI) calculated at 30, 50 and 70 days after transplanting were significantly influenced by different control methods as compared to control treatment during both the years of experiment (Table1). Maximum LAI was obtained in chemical control treatment at all the three times of recording the data, while the minimum LAI was obtained in control treatment (weedy check). Increase in LAI may be attributed to the optimum vegetative growth in these treatments, which increased the leaf area of the rice crop due to the efficient weed control. This allowed the rice plant to utilize nutrients, water and solar radiation fully without almost any interference. The results also suggested that sorghum water extract applied two times suppressed not only weeds but also the rice plants which reduced the leaf area index at 50 DAT as compared to one-time spray with sorghum water extract but this suppression was recovered at 70 DAT, as the treatments M4 and M5 become statistically equal at 70 DAT in producing leaf area. Irshad and Cheema (2002) reported promoting effects of different weed control methods on leaf area index. Determination coefficient of 0.8787 indicates a positive correlation between grain yield and leaf area index (Fig.2).

The methods to control barnyardgrass significantly affected the yield and yield components under study as compared to weedy check (Table1). Highest grain yield (4.32 t/ha) was obtained in herbicidal treatment This was statistically on a par with one hand pulling 20 days after transplanting. While both of the sorghum water extracts treatments, one spray 20 DAT and two sprays 20 and 40 DAT, followed these two methods. Similarly the control methods affected LAI, plant height, straw yield and harvest index in similar ways. Qayyum and co-workers (1989) and Zafar (1989), had also reported almost similar results. Maximum grain yield obtained in M3 and M2 treatments was possibly due to timely and effective control of barnyardgrass as compared to others. The increase in rice grain yield with these two treatments (M2 and M3) ranged 31-36% respectively with 90-95% control of dry weight of barnyardgrass. These results are in agreement with those of Azad et al. (1989) and Qayyum et al. (1989) who suggested that butachlor is very useful in increasing rice grain yield.

The application of sorghum water extract increased rice grain yields by 18-20% over control in both of the treatments i.e. one and two sprays. Relatively less grain yield in two sprays as compared to one-time spray with sorghum water extract may be due to less leaf area index in this treatment because of the suppression of vegetative growth (Table 1). The increase in grain yield of rice with sorghum water extract spray confirms the previous findings that sorghum water extract foliar sprays improved the wheat grain yield by 20-33% (Cheema et al. 2000).

An examination of table 2 revealed that all the barnyardgrass control method gave higher net income as compared to check (M1). Maximum net benefit was obtained by the application of butachlor and was followed by hand weeding treatment during both years. The cost in case of hand weeding was more than chemical control but the net benefits were less, so it was dominated by the herbicidal treatment (Table 3). Similarly two-time spraying with sorghum water extract having higher cost and lesser net benefits than sorghum water extract one spray and was dominated. As far as the marginal analysis is concerned one spray of sorghum water extract gave the 2790 % of marginal rate of return (MRR), while the MRR in case of herbicidal treatment was 560%. This analysis revealed that percent return for spending Rs. 200 was much greater with one spray of sorghum water extract than additional expenditure of Rs. 700 in herbicidal treatment. However chemical control treatment was economical due to higher net benefits.

Conclusion

Barnyardgrass could be effectively controlled with hand weeding and butachlor @ 1.2 kg a.i /ha, while sorghum water extract (as one- and two-time spraying) reduced the dry weight of barnyardgrass by 38-41%. Chemical control was most economical due to highest net benefits. One spray of sorghum water extract at 20 DAT improved rice grain yield by 20% with a relatively low cost as compared to other weed control methods. A foliar application of sorghum water extract may be an environment friendly way to minimize the interference of barnyardgrass to the rice crop.

Table 1. Parameters related to barnyardgrass and rice as affected by various methods for controlling barnyardgrass (Mean of year 1998 & 1999)

Treatments

BD
(m2)

BDB
(g/m2)

LAI
(30DAT)

LAI
(50DAT)

LAI
(70DAT)

RPH
(cm)

SY
(t/ha)

GY
(t/ha)

HI
(%)

M1 = Control
(Weedy check)

22.50 a1

662.5 a1
(-)

2.26 d1

5.11 c1

5.67 c1

119.19 c1

6.51 c1

3.18 c1
(-)

32.85 b1

M2 = Hand weeding
(One 20 DAT)

4.63 b

67.00 d
(90.0)2

2.83 b

5.58 b

7.43 a

137.86 a

8.85 a

4.16 a (31.0) 2

31.93 c

M3 = Chemical control
(Butachlor pre em. @1.2 kg/ ha)

1.63 c

36.38 e
(95.0)

2.93 a

5.85 a

7.70 a

139.93 a

9.16 a

4.32 a
(36.0)

31.98 c

M4 = Sorghum water extract
(1 Spray, 20 DAT)

22.00 a

414.2 b
(38.0)

2.74 c

5.53 b

6.26 b

135.24ab

7.62 b

3.83 b
(20.0)

33.42 b

M5 = Sorghum water extract
(2 Sprays, 20 & 40 DAT)

22.25 a

388.8 c
(41.0)

2.70 c

5.17 c

6.16 b

130.75 b

6.63 c

3.76 b
(18.0)

36.06 a

SE

0.9

8.80

0.03

0.09

0.11

1.78

0.16

0.06

0.26

1Values with the same letters in column are not different at P<0.05. 2Values given in parenthesis show percent decrease or increase in ratio to control. DAT = Days After Transplanting. SE = Standard error. BD=Barnyardgrass density. BDB= Barnyardgrass Dry Biomass. LAI= Leaf Area Index. RPH=Rice Plant Height. SY= Straw Yield. GY=Grain Yield. HI= Harvest Index

Table 2. Economic analysis of various barnyardgrass control methods in fine rice. (Mean of 1998&1999)
(A partial budget)

Components

M1

M2

M3

M4

M5

Grain yield (t/ ha)

3.18

4.16

4.32

3.83

3.76

Adjusted yield (t/ha)

2.78

3.76

3.92

3.43

3.36

Grain Value (1000 Rs. /ha)

22.94

31.02

32.34

28.30

27.72

Straw Yield (t /ha)

6.51

8.85

9.16

7.62

6.63

Straw Value (1000 Rs. /ha)

2.44

3.32

3.44

2.86

2.49

Gross benefits (1000 Rs. /ha)

25.38

34.34

35.78

31.16

30.21

Weeding cost (Rs. /ha)

0

1000

0

0

0

Herbicide cost (Rs. /ha)

0

0

750

0

0

Sorgaab cost (Rs. /ha)

0

0

0

50

100

Labour charges (Rs. /ha)

0

0

100

100

200

Sprayer rent (Rs. /ha)

0

0

50

50

100

Variable cost (Rs. /ha)

0

1000

900

200

400

Net benefits (1000 Rs. /ha)

25.38

33.34

34.88

30.96

29.81

M1 = control (without weeding), M2 = hand pulling [Once 20 days after transplanting (DAT)], M3 = Chemical control (Butachlor pre em. @ 1.2 kg a.i /ha), M4 = Sorgaab one spray 20 DAT, M5 = Sorgaab two sprays 20 & 40 DAT. Adjusted yield = Harvesting and threshing charges = 0.4 t /ha. Grain price = Rs.8250 / t. Straw price = Rs. 375/ t. Ten persons required for weeding a hectare (Rs.100 /person/day. 2.5-lit /ha. Rs.= Rupees

Table 3. Marginal and dominance analysis (Mean of 1998&1999)

Components

M1

M4

M5

M3

M2

Variable cost1 (Rs /ha)

0

200

400

900

1000

Net benefits (1000 Rs /ha)

25.38

30.96

29.81

34.88

33.34

Marginal costs2 (Rs /ha)

-

200

-

700

-

Marginal net benefits3
(1000 Rs /ha)

-

5.58

D

3.92

D

Marginal rate of return4 (%)

-

2790

-

560

-

M1 = control (without weeding), M2 = hand pulling [Once 20 days after transplanting (DAT)], M3 = Chemical control (Butachlor pre em. @ 1.2 kg a.i /ha), M4 = Sorgaab one spray 20 DAT, M5 = Sorgaab two sprays 20 & 40 DAT.

1It is the sum of all costs (both costs and opportunity costs) that for a particular treatment. 2The increase in variable cost, which occurs in changing from one production alternative to another. 3The increase in net benefits, which can be obtained by changing from one production alternative to another. 4Marginal net benefits / Marginal costs x 100, D = Dominated treatment, Rs. = Rupee

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