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Allelopathic effects of poplar (Populus deltoides Bartr Ex Marsh): an assessment on the response of wheat varieties under laboratory and field conditions

D.P.S. Nandal and A. Dhillon

Department of Forestry CCS Haryana Agricultural University, Hisar-125 004, India

Abstract

A field experiment with ten wheat varieties (UP2338, HD2687, WH147, WH283, WH542, WH157, HD2329, PBW343, WH896, WH533) and four poplar spacings (5 x 4 m, 10 x 2.5 m, 15 x 2.5 m, control) and bioassay studies with four poplar leaf extract concentrations of 0, 5, 10 and 20 per cent was carried out at CCS Haryana Agricultural University, Hisar (India) during 1999-2000. Poplar, which is the most important agroforestry tree species of northwest India, was four and half years old at the time of experimentation to screen and identify wheat varieties suitable for cultivation under different shade levels of poplar. Durum wheat variety WH896 out yielded most of the aestivum wheat varieties except WH-542 at all the spacings of poplar. The grain yield of all the varieties increased significantly with increasing tree spacing. Aqueous extracts of poplar leaves adversely affected the germination and seedling growth of some wheat varieties at high extract concentration. However, the germination of WH-896, WH-157 and HD-2329 wheat varieties remained unaffected at all the concentrations of leaf extract. Similarly shoot length of all varieties except UP-2338, HD-2687, WH-147 and WH-157 remained unaffected at all extract concentrations. Poplar leaf extracts at lower concentrations of 5 per cent stimulated the shoot length of UP-2338, HD-2687 and WH-147 varieties. Root length of all the varieties except WH-147 and HD-2338 was stimulated at lower leaf extract concentration of 5 per cent. Thus, such studies may help in identifying suitable wheat variety and amount of leaf litter to be retained in the field for higher productivity in poplar based agri-silviculture system.

Media Summary

Poplar is an important tree in agri-silviculure in India yet its leaf extracts can inhibit germination of wheat grown in the interspaces.

Keywords

allelopathy agri-silviculture, poplar, wheat

Introduction

Poplar is the most successful agroforestry tree species in India and produces extremely high productivity of up to 60 m3/ha/yr. The ubiquitous presence of poplars in the farmlands of Punjab, Haryana, Western Uttar Pradesh and Tarai region of Uttranchal, is enough testimony to the wide acceptance of poplar by the farmers. A lot of tree-crop combinations are practised by the farmers in poplar based agroforestry system. Wheat during the winter season is most widely cultivated crop in the interspaces of poplar. However, variable performance of wheat varieties in association with various tree species has been reported by many workers (Nandal et al., 1999; Gill, 1994). The present experiment was, therefore, planned to screen the existing wheat varieties under different shade levels of poplar and to correlate their field performance with allelopathic effect of poplar leaf extract in bioassay studies.

Materials and Methods

Wheat varietal screening studies were conducted during 1999-2000 from November to April at the research farm and laboratory of Forestry Department, CCS Haryana Agricultural University, Hisar (India). The soil of the experimental fields was sandy loam in texture and slightly saline in reaction (pH 8.2). The available nitrogen, phosphorus and potassium were 195, 7 and 225 in 5x4 m spacing; 168, 5 and 153 in 10 x 2.5 m spacing; 163, 5 and 150 in 15 x 2.5 m spacing and 155, 4 and 225 kg/ha in control, respectively. Poplar plantation having 5 x 4 m, 10 x 2.5 m and 15 x 2.5 m spacing was raised in February 1995 and was four years and 9 months old at the time of start of this experiment.

Ten varieties of wheat viz., WH-157, HD-2687, WH-283, WH-533, WH-542, WH-147, WH-896, HD-2329, UP-2338 and PBW-343 were sown in two different environments, i.e., agriculture and agrisilviculture on November 13 in 1999-2000. A uniform seed rate of 125 kg/ha, row spacing of 22 cm and fertilizer dose of 120 kg N/ha and 60 kg P2O5/ha was used. Three post-sowing irrigations were applied both in poplar sown wheat and pure crop of wheat.

In laboratory studies, all the varieties of wheat grown in the field were screened for allelopathic effect of poplar leaf extracts by using four extract concentrations of control, 5, 10 and 20 per cent. The treatments were replicated four times in a completely randomized block design. The aqueous extracts of senescent oven dried leaf samples of poplar were prepared by soaking 5, 10 and 20 per cent by weight in distilled water for 48 hrs. Aqueous extract thus obtained was filtered through Whatman No.1 filter paper. Twenty seeds of each variety were placed in petridishes lined with doubled layer of filter paper. The seeds were moistened with 10 ml of the respective extract on first day and 5 ml on subsequent days as and when required. Distilled water was used as control. Germination and growth parameters were recorded on the seventh day after sowing.

Results and Discussion

Bioassay studies: Aqueous leaf extracts of poplar leaves significantly influenced the germination of wheat varieties (Table 1). Mean germination values of wheat varieties showed that variety UP-2338 recorded the highest and WH-283 the lowest germination under the influence of aqueous extracts. Wheat variety WH-896 recorded the maximum shoot and root lengths, however, its root length was at par with wheat varieties WH-533, WH-147 and HD-2329. Germination of wheat varieties decreased significantly at higher concentrations of 10 and 20 per cent over control. Similarly, shoot and root length of wheat varieties (Table 2) was stimulated at lower extract concentration of 5 per cent. At higher concentration aqueous extracts had no effect on shoot length but significantly retarded the root length of wheat varieties. The decrease in germination and root length of wheat varieties at higher concentration might be due to excess of inhibitory allelochemicals present in the extracts. Melkania (1984) has also reported an inhibitory effect of P. deltoides leaf, soil leachates and rain drip on the seed germination and radicle growth in wheat. The allelopathic potential of poplar leaf litter has been reported due to the presence of Catechol and benzoic acid inhibitors in its leaves (Olsen et al., 1971). Allelochemicals may stimulate or inhibit the plant growth depending upon their concentration (Osvald, 1950).

The interaction affect between wheat varieties and extract concentrations on germination and growth of wheat varieties (Table 1) showed that up to 10 per cent extract concentration only germination of WH-542 was reduced significantly at 10 per cent extract concentration. However, at 20 per cent extract concentration, significant reduction in germination was reduced in UP-2338, HD-2687, PBW-343 and WH-533 varieties of wheat. It might be due to more susceptibility of these varieties to the allelochemicals of poplar. The shoot length of wheat varieties UP-2338, HD-2687 and WH-147 increased significantly at lower concentration of 5 per cent. Harmful effect of poplar leaf extracts at higher concentration might be due to excess of inhibitory allelochemicals present in the extract. Leaf extracts of poplar had inhibitory effect on the shoot length of wheat variety WH-157 at all extract concentrations. Root length of all wheat varieties, except UP-2338 and WH-147 increased significantly at lower extract concentration of 5 per cent and decreased significantly at higher extract concentrations.

Table 1: Effect of different poplar leaf extract concentrations on germination (%), shoot and root length (cm) of wheat varieties

Wheat

Extract concentration (%)

Mean

varieties

0

5

10

20

 

G

SL

RL

G

SL

RL

G

SL

RL

G

SL

RL

G

SL

RL

WH-2338

94

7.5

12.4

96

13.0

11.4

99

7.7

6.3

91

7.6

7.6

95

9.0

9.4

HD-2687

91

7.8

6.8

89

10.9

12.0

86

9.2

7.5

78

8.5

7.0

86

9.1

8.3

WH-147

94

7.7

11.8

93

10.8

12.1

92

8.7

7.3

84

8.7

10.0

91

9.0

10.3

WH-283

76

9.1

6.0

74

8.3

11.0

74

7.9

4.5

76

8.1

5.1

75

8.4

6.7

WH-542

94

7.9

9.2

90

8.3

12.9

81

8.8

6.8

81

8.5

7.6

86

8.4

9.1

WH-157

89

10.3

9.7

88

8.5

14.1

91

8.3

6.5

86

8.3

5.3

88

8.8

8.9

HD-2329

94

10.1

8.8

92

10.8

13.1

88

10.0

7.7

87

9.1

10.1

90

10.0

9.9

PBW-343

97

10.0

8.8

93

9.2

12.0

92

9.9

7.0

76

10.7

7.8

90

9.9

8.9

WH-896

84

10.9

8.3

89

10.4

13.9

86

11.5

9.9

88

10.7

9.9

87

10.9

10.5

WH-533

96

9.3

13.9

93

9.0

11.2

93

9.1

7.6

74

9.4

7.4

89

9.2

10.0

Mean

90.9

9.1

9.6

89.7

9.9

12.4

88.2

9.1

7.1

82.1

9.0

7.8

-

-

-

CD at 5% for

     
 

Germination

Shoot length

Root length

Spacing

2.74

0.83

0.63

Varieties

1.73

0.53

0.40

Spacing x Varieties

5.48

1.77

1.27

Field studies: Data presented in Table 2 revealed that mean grain yield of what variety WH-896 was significantly higher than all other varieties of wheat. Second best variety, WH-542 also yielded significantly higher grain yield than other varieties of wheat. Wheat variety WH-283 produced minimum grain yield among all the varieties. Mean grain yield of wheat was significantly less under all the spacings of poplar as compared to control wheat. The reduction under poplar might be attributed to competition of poplar with wheat for various growth resources especially sunlight during the early stages of growth. There was 56, 41 and 35 per cent reduction in sunlight under 5 x 4 m, 10 x 2.5 m and 15 x 2.5 m poplar spacings, respectively. Singh et al. (2004) have also reported strong relationship between wheat yield and PAR in Ceiba pentandra based agroforestry system. Grain yield also increased significantly with increasing spacings of poplar due to reduced competition for growth resources.

Table 2: Grain yield (q/ha) of wheat varieties under different spacings of poplar

Wheat

Poplar spacings (m)

Mean

varieties

5 x 4

10 x 2.5

15 x 2.5

Control

 

WH-157

11.3

18.9

26.5

37.8

23.6

HD-2687

10.5

19.4

26.0

37.3

23.3

WH-283

9.4

14.0

19.0

26.7

17.3

WH-533

13.0

21.3

29.2

38.4

25.5

WH-542

17.6

25.8

34.2

42.8

30.1

WH-147

12.5

21.6

32.4

45.0

27.9

WH-896

17.4

26.8

36.7

49.7

32.7

HD-2329

14.6

23.4

31.7

41.7

27.9

UP-2328

10.8

18.5

25.6

33.7

22.2

PBW-343

13.6

21.8

30.3

38.9

26.2

Mean

13.1

21.2

29.2

39.2

-

CD at 5% for

       

Spacing

0.8

     

Varieties

1.4

     

Spacing x Varieties

2.8

     

Interaction effect between tree spacings and wheat varieties showed that in monoculture (control) wheat variety WH-896 out-yielded all other wheat varieties, however, under all the spacings of poplar, it was at par with wheat variety WH-542. It indicated that wheat variety WH-542 has maximum tolerance to moisture, nutrient and shade competition of poplar. At wider spacings of 10 x 2.5, wheat variety HD-2329 and at 15 x 2.5 m, WH-147 and HD-2329 varieties were also at par with WH-542. Nandal et al. (1999) and Singh et al. (1993) have also reported differential response of wheat varieties sown under poplar.

Bioassay vs Field studies: No relationship was found between bioassay and field studies. In bioassay studies, wheat variety WH-542 which showed reduced germination at higher extract concentration compared to no effect on germination of wheat variety WH-896 produced grain yield at par with WH-896 under all the spacings of poplar. Because the germination count of wheat variety WH-542 under different poplar spacings and in control field was identical. Likewise, the germination of other varieties under different spacings of poplar and in control was also identical. The interaction effects in bioassay and field studies were also different.

References

Gill, A.S. 1994. Effect of trees on the yield of wheat varieties in semi-arid conditions. Van Anusandhan 9: 8-12.

Melkania, N.P. 1984. Influence of leaf leachates of certain woody species in agricultural crops. Indian Journal of Ecology 11: 82-86.

Nandal, D.P., Rana, P. and Kumar, A. 1999. Growth and yield of wheat (Triticum aestivum) under different tree spacings of Dalbergia sissoo based agrisilviculture. Indian Journal of Agronomy 44: 256-260.

Olsen, R.A., Odham, G. and Linderberg, G. 1971. Aromatic substances in leaves of Populus trimula inhibiters of mycorrhizal fungi. Physiol. Plant. 25: 122-129.

Osvald, H. (1950) On antagonism between plants. Proceedings of the 7th International Botanical Congress, Stockholm, Sweden, pp167-171

Singh, A., Dhanda, R.S. and Ralhan, P.K. 1993. Performance of wheat varieties under poplar plantation in Punjab. Agroforestry Systems 22: 83-86.

Singh, U.S., Naugraiya, M.N., Sahoo, M.L. and Puri, S. 2004. Evaluation of eco-physiological variations on wheat productivity under varying densities of Ceiba pentandra (L.) Gaertn. Indian Journal of Agroforestry 6: 57-59.

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