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African Crop Science Journal
African Crop Science Society
ISSN: 1021-9730 EISSN: 2072-6589
Vol. 6, Num. 2, 1998, pp. 189-195
African Crop Science Journal, Vol

African Crop Science Journal, Vol. 6. No. 2, pp. 189-195, 1998

SHORT COMMUNICATION

EFFECTS OF THINNING AFTER ANTHESIS ON GROUNDNUT GROWTH, YIELD AND YIELD COMPONENTS

A.J.P. Tarimo and F.P.C. Blamey1

Department of Crop Science and Production, Sokoine University of Agriculture, P.O. Box 3005, Morogoro, Tanzania
1Department of Agriculture, Queensland University, Queensland, Brisbane Q4072, Australia

(Received 15 September, 1997; accepted 10 January, 1998)

Code Number:CS98021
Sizes of Files:
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ABSTRACT

This experiment was carried out to study groundnut (Arachis hypogaea L.) response to enhanced penetration of photosynthetically active radiation (PAR) into the canopy during reproductive growth in southeast Queensland, Australia. The experiment was located at the University of Queensland's Redland Bay Farm. Two groundnut cultivars (Improved Virginia Bunch and Red Spanish) were grown at a population of 42 plants m-2) and thinned at intensities of either 0% (control), 33%, 50%, 66% or 75% after anthesis (42 days after planting). The results show that thinning reduced PAR intercepted during reproductive growth, but slightly increased radiation use efficiency (Ec) with 33% plant removal in Red Spanish. Removal of either 0%, 33% or 50% of plants resulted in relatively similar total dry mass (TDM) and economic yields at maturity. Dry mass partitioning to reproductive sinks was largely unaffected by thinning after anthesis. It is concluded that removal of up to 50% of groundnut plants from the initial population of 42 m-2 after anthesis did not significantly reduce TDM or economic yield at maturity.

Key Words: Arachis hypogaea, economic yield, photosynthetically active radiation, thinning intensity, total dry mass

RÉSUMÉ

Cette expérimentation a été effectuée en vue d'étudier la réaction de l'arachide (Arachis hypogea L.) à la pénétration intense de la radiation photosynthétiquement active (PAR) dans la canopie pendant la croissance reproductive au sud-est de Queensland en Australie. L'expérimentation a eu lieu à la ferme de Redland Bay de l'Université de Queensland. Deux cultivars de l'arachide (l'érigé amélioré de Virginie et l'Espagnol Rouge) ont poussé jusqu' à une population de 42 plantes/m2. Ils ont été ensuité soumis au démariage à 0% (temoin), 33%, 66% ou 75% après l'anthèse (42 jours après le sémis). Les résultats montrent que le démariage reduisait le PAR intercepté pendant la croissance reproductive mais augmentait légèrement l'efficacité de la radiation utilisée (Ec) avec un démariage de 33% des plantes pour le cultivar Espagnol Rouge. Le démariage de 0%, 33% ou 50% des plantes aboutit à une masse totale sèche (TDM) et aux rendements économiques assez semblables à la maturité. La répartition de la matière sèche dans le bloc de stockagede la reproduction n'était pas vraiment affectée par le démariage après l'anthèse. Il en résulte qu'un démariage d'un maximum de 50% des plantes d'arachide à partir d'une population initiale de 42/m2 après l'anthèse ne réduitsait pas de façon significative la mass sèche totale (TDM) ou le rendement économique à la maturité.

Mots Clés: Arachis hypogaea, rendement économique, radiation photosynthétiquement active, intensité de démariage, masse sèche totale

INTRODUCTION

Plant growth and yield can be manipulated by changing the supply of growth resources such as light, water and soil nutrients (Watson, 1958; Prine, 1971; Williams, 1979; Muchow and Charles-Edwards, 1982). In groundnut (Arachis hypogaea), thinning during early reproductive growth has been shown to increase biological yield, peg+pod number, pod number per plant, harvest index (HI) and economic yield at maturity (Williams, 1979). The time of thinning affects the magnitude of these responses. Muchow and Charles-Edwards (1982) noted in mung bean (Phaseolus aureus) that increases in biological and economic yields per plant after thinning were dependent upon the thinning intensity which regulated light penetration into the remaining crop canopy. It has been shown also that thinning after anthesis in many crops results in greater growth, improved dry mass (DM) partitioning to economic yield and increased economic yield per plant at maturity (Prine, 1971; Williams, 1979).

Experiments on groundnut have shown marked responses to plant population density in terms of dry mass accumulation, economic yield and yield components (Tarimo, 1992). Dry mass partitioning to plant components usually changes only slightly with changes in plant population density, although pod and kernel yields could increase because of increased HI. Usually, the effects of plant population density on growth are more evident during the vegetative and early reproductive growth stages, implying that any variation in plant numbers after anthesis would have similar effects to the plant density established at sowing.

Currently, information is scarce on the effects of thinning after anthesis on groundnut growth and yield; such information would be useful in forecasting crop losses associated with damage by crop pests and diseases during a cropping season. This study examined the effects of thinning after anthesis on groundnut growth, DM partitioning, yield and yield components. The study was intended to generate essential data for simulating the impact of pests and foliar diseases on seasonal yield variation in groundnut.

MATERIALS AND METHODS

A field experiment was conducted at the University of Queensland Redland Bay Farm (27° 37' S; 153° 17' E) in southeast Queensland, Australia during the cropping season of 1989/90. Two cultivars (Improved Virginia Bunch (IVB) and Red Spanish were studied. Sowing was carried out on 21 November, 1989 using manual labour. An initial plant spacing of 60 x 4 cm was used, resulting in a plant population density of 42 plants m-2.

Thinning was manually carried out on 21 December, 1989 (42 days after planting (DAP)), removing either 0%, 33%, 50%, 66%, or 75% of the plants within a row. The percentages were achieved by: no plant removal; removal of every third plant while skipping two plants, and removal of every alternate plant; removal of every two plants skipping one plant or removal of every three plants skipping one plant within a row. The new spacings resulted in plant population densities of 42, 28, 21, 14 and 10 plants m-2.

Treatments were arranged in a randomised complete block design (RCBD) with three replications. The plot size was 3.2 x 3.0 m for all treatments. Five rows each 3.2 m long were established per plot to allow for enough plants to be sampled at each harvest. In all, four harvests were carried out during the season at 42, 62, 83, and 152 DAP. At each harvest, data were recorded for total dry mass (TDM) per plant, photosynthetically active radiation (PAR) intercepted (using the method of Muchow and Kerven, 1977), stem dry mass/plant, leaf dry mass/plant, pegs/plant, pods/plant, kernels/plant, pod dry mass/plant and kernel dry mass. From these data, various secondary data were calculated (Tables 1 to 3). The radiation use efficiency (Ec) was calculated as TDM/cumulative PAR measured during the growth period (days after sowing). Crop growth rate (CGR) was calculated as TDM m-2/growth period (days). All data were analysed by the analysis of variance (ANOVA) technique.

TABLE 1. Change In total dry mass (TDM), cumulative photosynthetically active radiation (PAR) intercepted, radiation use efficiency (Ec) and crop growth rate (CGR) at three intervals during growth (days after planting. DAP) of two groundnut cultivars thinned at five intensities (%) after anthesis (42 DAP)

Cultivar/Character

Thinning intensity (%)

Mean

0

33

50

66

75

42-62 DAP

Improved Virginia Bunch

TDM (g m-2)

647

528

338

283

236

406

PAR (MJ m-2)

401

383

322

280

234

324

Ec (g MJ-1)

1.61

1.38

1.04

1.01

1.00

1.21

CGR (g m-2 d-1)

32.35

26.42

16.90

14.15

11.81

20.33

Red Spanish

TDM (g m-2)

542

395

409

316

240

380

PAR (MJ m-2)

375

316

309

250

202

291

Ec (g MJ-1)

1.45

1.25

1.32

1.26

1.18

1.29

CGR (g m-2 d-1)

27.12

19.73

20.45

15.82

12.00

19.03

63-83 DAP

Improved Virginia Bunch

TDM (g m-2)

302

348

669

376

435

426

PAR (MJ m-2)

463

453

449

414

402

436

Ec (g MJ-1)

0.65

0.76

1.49

0.91

1.08

0.98

CGR (g m-2d-1)

14.39

16.58

31.88

17.91

20.73

20.2P

Red Spanish

TDM (g m-2)

436

510

357

258

106

336

PAR (MJ m-2)

449

427

432

370

297

395

Ec (g MJ-1)

0.97

1.20

0.86

0.69

0.36

0.81

CGR (g m-2d-1)

20.79

24.30

17.50

12.31

5.03

15.99

84-152 DAP

Improved VIrginia Bunch

TDM (g m-2)

295

347

292

134

310

276

PAR (MJ m-2)

1025

983

971

838

852

934

Ec (g MJ-1)

0.29

0.37

0.30

0.15

0.36

0.29

CGR (g m-2d-1)

4.28

5.03

4.23

1.93

4.49

3.99

Red Spanish

TDM (g m-2)

-70

270

291

351

246

218

PAR (MJ m-2)

941

876

890

766

576

810

Ec (g MJ-1)

-0.07

0.31

0.32

0.46

0.41

0.29

CGR (g m-2 d-1)

-1.01

3.91

4.22

5.09

3.57

3.15

LSD (P<0.05) Cultivar x Thinning intensity

DAP

42-62

62-83

83-152

TDM (g m-1)

ns

220

ns

PAR (MJ m-2)

ns

25

84

Ec (g MJ-1)

ns

0.53

ns

CGR (g m-2d-1)

ns

10.50

ns

ns = not significant

TABLE 2. Peg+pod number; pod number and ratio of pod number to peg+pod number m-2 at two growth stages after planting. DAP) during growth of two groundnut cultlvars thinned at five intensities (%) after anthesis (42 DAP)

Cultivar/Character

Thinning intensity (%)

Mean

0

33

50

66

75

83 DAP

Improved Virginia Bunch

Pegs+pods (m-2)

1215

1124

1190

1064

1057

1130

Pods number (m-2)

262

332

332

262

246

297

Pods/(pegs+pods)

0.21

0.30

0.32

0.25

0.24

0.27

Reproductive sink (%)

6.7

7.5

12.4

10.5

10.7

9.6

Vegetative sink (%)

93.2

92.5

87.6

89.5

89.3

90.4

Red Spanish

Pegs+pods (m-2)

1626

1332

1203

903

591

1130

pod number (m-2)

608

576

458

306

267

443

Pods/(pegs+pods)

0.39

0.43

0.37

0.34

0.46

0.40

Reproductive sink (%)

21.4

24.8

23.3

19.8

21.3

22.1

Vegetative sink (%)

78.6

75.1

76.7

80.2

78.7

77.9

132 DAP

Improved Virginia Bunch

Pegs+pods (m-2)

676

594

703

621

1015

722

Pod number (m-2)

568

515

602

413

590

538

Pods/(pegs+pods)

0.83

0.89

0.86

0.74

0.58

0.78

Reproductive sink (%)

42.2

38.8

464

42.6

46.3

43.6

Vegetative sink (%)

57.8

61.2

53.9

57.4

51.6

58.4

Red Spanish

Pegs+pods (m-2)

899

1041

1007

851

638

387

Pod number (m-2)

777

387

813

623

448

730

Pods/(pegs+pods)

0.38

0.95

0.81

0.75

0.72

0.62

ReIxoductive sink (%)

46.7

03.8

50.5

46.9

47.8

49.5

Vegetative sink (%)

51.3

46.2

49.5

53.1

51 2.

50.4

LSD (P< 0.05)

DAP

Thinning Intensity

Cultivar

Interaction

Thinning Intensity

Cultivar

Interaction

Pegs+pods (m-2)

320

ns

ns

ns

158

349

Pod number (m-2)

124

79

ns

158

38

220

Pods/(pegs+pods)

ns

0.05

ns

0.11

ns

ns

Reproductive sink (%)

ns

3.5

ns

ns

4.8

ns

Vegetative sink (%)

ns

3.5

ns

ns

4.8

ns

ns = not significant

TABLE 3. Kernel yield and yield components at two growth stages (days after planting, DAP) of two groundnut cultivars thinned at five intensities (%) after anthesis (42 DAP)

Cultivar/Character

Thinning intensity (%)

0

33

50

66

75

Mean

83 DAP

Improved Virginia Bunch

Kernel DM (g m-2)

24

20

38

15

16

23

Harvest index (%)

1.9

1.9

3.2

1.9

2.2

2.2

Shelling (%)

29.5

24.7

26.2

18.2

19.3

23.6

Kernels/pod

0.71

0.72

0.61

0.46

0.52

0.60

Kernels m'

184

244

235

119

130

183

Kernel size (g)

0.13

0.09

0.16

0.12

0.12

0.13

Red Spanish

Kernel DM (g m-2)

152

166

125

77

45

113

Harvest index (%)

12.5

15.7

13.6

11.4

11.1

12.9

Shelling (%)

58.7

63.2

52.1

57.8

51.8

56.7

Kernels/pod

1.35

1.42

1.25

1.29

1.09

1.28

Kernels m-2

827

813

633

388

292

591

Kernel size (g)

0.18

0.20

0.19

0.19

0.15

0.18

152 DAP

Improved Virginia Bunch

Kernel DM (g m-2)

509

425

489

283

370

415

Harvest index (%)

32.6

29.2

33.6

31.2

34.6

32.2

Shelling (%)

77.4

74.7

72.9

73.1

71.4

73.9

Kernels/pod

1.44

1.43

1.33

1.17

1.13

1.30

Kernels m-2

815

731

788

444

677

691

Kernel size (g)

0.63

0.57

0.62

0.63

0.55

0.60

Red Spanish

Kernel DM (g m-2)

458

594

478

385

256

434

Harvest index (%)

40.5

44.5

40.2

38.4

38.8

40.5

Shelling (%)

83.1

82.8

79.7

81.8

81.1

81.7

Kernels/pod

1.46

1.54

1.54

1.63

1.55

1.55

Kernels m-2

1134

1511

1256

1019

697

1123

Kernel size (g)

0.40

0.39

0.38

0.38

0.37

0.38

LSD (P< 0.05)

DAP

83

152

Thinning Intensity

Cultivar

Interaction

Thinning intensity

Cultivar

Interaction

Kernel DM

40

25

57

112

ns

ns

Harvest index (%)

ns

2.5

ns

ns

3.8

ns

Shelling (%)

ns

6

ns

3

2

ns

Kernels/pod2

ns

0.15

ns

ns

0.12

ns

Kernels (m-2)

196

124

ns

224

142

317

Kernel size (g)

ns

0.02

0.04

ns

0.04

ns

ns = not significant

RESULTS AND DISCUSSION

Crop growth and development after thinning.

Total dry mass (TDM) increments early after thinning (42-62 DAP) were reduced as were time for PAR intercepted, radiation use efficiency (Ec) and crop growth rate (CGR) in both cultivars. Total dry mass decreased with increases in thinning intensity mainly because of reduced plant population (Table 1). After this period, there was considerable compensation in growth where < 66% of the plants had been removed, thus resulting in large changes in TDM m-2. At maturity, therefore, TDM in those treatments were similar or slightly greater than the control. With higher intensity of thinning (>50%), however, growth compensation in the remaining plants was unable to compensate for reduced plant population density. Watson (1958), Prine (1971) and Muchow and Charles-Edwards (1982), reported similar results among other crops. Williams (1979) reported an increase in TDM per plant by maturity with 75% plant removal after anthesis in groundnut as a result of growth compensation in the low plant population density environment.

At maturity, TDM was highest with 33% plant removal in the Red Spanish because of greater growth compensation than in the Improved Virginia Bunch. In the latter cultivar, growth compensation did not result in TDM being greater than that of the control (Table 1). Overall, the differences in TDM between 33% plant removal and the control were small only in Improved Virginia Bunch. In both cultivars, differences in TDM accumulation among treatments after thinning resulted from differences in cumulative PAR intercepted and Ec (Table 1).

Radiation use efficiency was slightly reduced with high thinning intensity in Improved Virginia Bunch, contributing to the decrease in TDM at maturity when compared with the control (Table 1). Charles-Edwards et al. (1986) noted that TDM decreased under conditions of low Ec during crop growth.

These results have shown that up to 50% plant removal in groundnut after anthesis may result in only small changes in TDM at maturity because of growth compensation in the low plant population density environment. A thinning intensity of >50% would reduce TDM accumulation m-2 in the groundnut.

Dry mass partitioning. Dry mass partitioning to vegetative plant components decreased slightly with increased thinning intensity (Table 2). The high proportion of TDM partitioned to vegetative components among treatments in both cultivars suggests that assimilate production was in excess of that required for filling pods (Williams et al., 1975; Muchow and Wilson, 1976; Williams, 1979). On the other hand, growth of the reproductive sink per plant increased with increased thinning intensity, thus resulting in significant compensation for the numbers of pegs and pods m-2 at maturity with <66% plant removal (Table 2). Similar conclusions were reported by Prine (1971), Muchow and Wilson (1976) and Williams (1979). A thinning intensity >50% reduced both the number of pegs and pods m-2 due to increased partitioning to vegetative growth (Table 2).

Throughout crop growth, treatment interaction effects on DM partitioning (%) to the reproductive sink were not significant (Table 2). This suggests that the priority of dry mass partitioning to plant components is largely independent of plant removal after anthesis in groundnut. Thus, the variation in DM partitioning among the treatments was mainly due to cultivar differences in sink potential.

Kernel yield and yield components. Throughout reproductive growth, kernel yield decreased with increased thinning intensity in Improved Virginia Bunch (Table 3). In Red Spanish, however, highest kernel yield was observed with removal of 33% of the plants at anthesis. In both cultivars, kernel yield was significantly reduced with 66% plant removal.

Trends of kernel yield response to thinning intensity were similar to those of TDM for both cultivars. As reported by Muchow and Charles-Edwards (1982) in mung bean, factors affecting growth after anthesis in legumes would affect overall economic yield at maturity. Kernel yield, for example, was associated with increased harvest index (HI) throughout the reproductive growth period. Similarly, increased shelling percent was associated with increased kernel yields but only during the period prior to maturity (up to 116 DAP). At maturity, kernel yield and the shelling percentage did not show a clear pattern of response to thinning intensity. Both kernel HI and the shelling percentage, however, are useful components of variation in kernel yield among cultivars of groundnut.

In this study, increased kernel yield was associated with an increase in the number of kernels m-2. Individual kernel size did not show a clear pattern of response to thinning, although at 83 DAP differences in kernel yield were associated with differences in kernel size between the cultivars (Table 3). Initially, thinning only slightly reduced kernel size in both cultivars as reported earlier by Williams (1979). Muchow and Charles-Edwards (1982) showed in mung bean that seed size increased with increased Ec during pod filling and with greater relocation of assimilate from stems to pods. In the present study, groundnut yields were higher in cultivars with large kernels than in cultivars with small kernels at maturity. Larger kernels in thinned treatments probably resulted from increased assimilate partitioning to the reproductive parts when compared to the control.

CONCLUSIONS

Groundnut cultivars differed in response to thinning intensities after anthesis. Red Spanish showed greater compensation in growth following plant removal than Improved Virginia Bunch. In Improved Virginia Bunch, removal of 0, 33 and 50% of the plants resulted in similar TDM and economic yields at maturity. Overall, there were small differences in TDM at maturity in both cultivars with 0, 33 and 50% plant removal.

Crop growth rate and Ec decreased at thinning intensities >66% in both cultivars which resulted in reduced TDM and kernel yields at maturity.

ACKNOWLEDGEMENTS

This paper is part of a Ph.D. thesis submitted to the University of Queensland, Australia, under the supervision of the second author. The research was supported by a scholarship from the Australian International Development Assistance Bureau (AIDAB) offered to the senior author (1987-1992).

REFERENCES

Charles-Edwards, D.A., Doley, D. and Rimmington, G.M. 1986. Modelling Growth and Development. Academic Press, London. 235 pp.

Muchow, R.C. and Charles-Edwards, D.A. 1982. Analysis of the growth of mung beans at a range of plant population densities in tropical Australia. I. Dry matter production. Australian Journal of Agricultural Research 33:41-52.

Muchow, R.C. and Kerven, G.L. 1977. A low cost instrument for measurement of photo-synthetically active radiation in field canopies. Agricultural Meteorology 18:187-195.

Muchow, R.C. and Wilson, G.L. 1976. Photosynthetic and storage limitations to yield in sorghum (Sorghum bicolor L. (Moench)). Australian Journal of Research 27:489-500.

Prine, G. 1971. A critical period for ear development in maize. Crop Science 11:782-782.

Tarimo, A.J.P. 1992. Growth and Yield Response of Groundnut (Arachis hypogaea L.) to Plant Population Density and Thinning After Anthesis. Ph.D. Thesis, Queensland University. 240pp.

Watson, D.J. 1958. The dependence of net assimilation rate on leaf area index. Annals of Botany 22:37-54.

Williams, J.H. 1979. The physiology of groundnut (Arachis hypogaea L. cv. Egret). III. The influence of thinning at different stages of development on reproductive growth and development. Rhodesia Journal of Agricultural Research 17:457-462.

Williams, J.H., Wilson, J.H.H. and Bate, G.C. 1975. The growth and development of four groundnut (Arachis hypogaea L.) cultivars in Rhodesia. Rhodesia Journal of Agricultural Research, 13:131.

Copyright 1998, African Crop Science Society

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