J. Agronomy & Crop Science 160, 102—105 (1988)© 1988 Paul Parey Scientific Publishers, Berlin and HamburgISSN 0931-2250

Faculty of Agriculture, University of Peradeniya, Peradeniya, Sri Lanka

Seedling Growth of Cowpea and Mungbean as Affected by Seed Sizeand Seeding Depth

U. R. SANGAKKARA and P. BIELER

Authors' addresses: Dr. U. R. SANGAKKARA, Faculty of Agriculture, University of Peradeniya, Peradeniya,Sri Lanka, and Mr. P. BlELER, ETH Zurich, Institut fur Pflanzenwissenschaften, LFM 8092, Zurich,Switzerland.

With 3 tables

Receivedlune 10, 1987; accepted August 11, 1987

Abstract

The germination and seedling growth patterns of different sized seeds of cowpea and mungbean when plantedat different depths were evaluated by the modified Hiltner method. All seeds placed on the surface showedpoor seedling growth, although small seeds were less susceptible than larger seeds. Seedling growth of smallseeds declined rapidly beyond a planting depth of 4 cms, while the larger seeds showed similar results beyonda depth of 6 cms. The value in using uniform seed material and placing the seed at a uniform depth ispresented.

Introduction

The existance of a positive relationshipbetween seed characters and seedling vigour incrop species has been reported by variousresearchers (e.g. BLACK 1959, PERRY 1976).Amongst the seed characters, seed size iswidely considered to be a primary feature con-tributing to seedling vigour in most species(ARENS 1962, COCKS and DONALD 1973, PERRY

1976). Although larger seeds are reported toproduce healthy and vigourous seedlings, suc-cessful field establishment of crops depend onthe environmental factors and planting depth(MAYER and POLJAKOFF MAYBER 1982). Whileenvironmental factors are difficult to controlunder field situations, planting depth can bekept optimal to obtain successful seedlingestablishment. The effect of planting depth on

seedling establishment is associated with vig-our as the seedling requires greater vigour topenetrate through a thicker layer of soil ifplanted deep (POPAY and SAUNDERS 1975). Thisvigour could be associated with seed charac-ters, especially seed size, as suggested byJEEVANANDA and SENANAYAKE (1986).

Mung bean {Vigna radiata L.) and Cowpea{Vigna unguiculata Walp.) are the most widelycultivated grain legumes in Sri Lanka (Dept. ofAgriculture, 1986) and studies on seedingdepth and seedling emergence in relation toseed size which has a deterministic effect oncrop establishment are not widely reported.Thus, a study was carried out to identify therelationship between seed size and plantingdepth as shown by seedling emergence inmung bean and cowpea, using the modifiedHiltner test (FucHS 1981).

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Seedling Growth of Cowpea and Mungbean as Affected by Seed Size and Seeding Depth 103

washed river sand. The depth of the top layers in thefour trays were 2, 4, 6 and 8 cms respectively. Thusthe sand cover over the seeds were either 0, 2, 4, 6 or8 cms.

Table 1. 100 seed weight of the selected varieties ofCowpea and Mungbeans

Materials and Methods

The study was carried out at the University ofPeradeniya, in a green house. The environmentalconditions during the experimental period were26.4 ± 1.2 °C temperature, 85.6 % ± 2.8 % rela-tive humidity and a 11—12 hour day length.

Varieties and Seed Selection

The species selected were mung bean and cowpea,and the varieties were selected from each speciesbased on seed size. Thus the varieties of cowpea wereSelection TV X 193398 (large seeded) and Arlington(small seeded). The large and small seeded varietiesof mung bean were MI 4 and selection 7715 respec-tively.

Seeds of each variety were divided into large,medium and small seeds visually and the 100 seedweight of each category determined (Table 1). Allcharacters were tested for germination by techniquesof ISTA (1976). The mean germination of allcategories was 98.3 % ± 0.97 %.

Seed Establishment

One hundred seeds were obtained from the large,medium and small seed lots of each variety andplaced in three equidistant rows in one germinationtray (50 x 30 cm) containing a 1 cm thick layer ofwashed river sand (particle size 2 3 mm). Five suchtrays were prepared per replicate of each variety.

Seeds of one tray were not covered. The seeds ofthe other four trays were covered with layers of

Table 2. Effect of seed size and planting depth on seedling emergence in cowpea 16 days after establishment

Species and variety

Cowpea

Selection TV X 193398SmallMediumLarge

Arlington

SmallMediumLarge

Mungbean

MI 4

SmallMediumLarge

Selection 7715

SmallMediumLarge

100 seed weight (g) ± S.E.

10.646 ± 0.58412.114 ± 0.72515.043 ± 0.910

5.685 + 0.0437.114 ± 0.0749.634 ± 0.020

5.143 ± 0.1245.998 ± 0.0836.798 ± 0.121

2.623 ±0.2103.569 ± 0.1434.321 ± 0.094

Depthof planting (cm)

Small seedsNormal Abnormal Dead

Number of seedlings

Medium seedsNormal Abnormal Dead

Large seedsNormal Abnormal Dead

SelectionTV X 193398

02468

Sx

Arlington

02468

0.078.580.353.8

0.01.8

18.594.365.312.40.01.9

10.52.31.2

35.753.7

5.4

14.30.5

24.460.819.75.2

89.519.218.510.546.3

3.0

67.25.2

10.326.880.32.8

0.074.389.874.810.50.9

10.390.886.740.76.31.6

0.01.80.0

15.355.44.9

15.60.00.4

28.548.8

0.9

10023.410.29.9

34.16.1

74.19.2

12.930.844.9

3.8

0.075.687.380.626.1

0.4

4.687.692.066.718.84.1

0.02.41.21.8

69.43.9

18.40.80.0

29.559.1

2.0

10022.011.57.64.54.4

77.011.68.0

3.822.12.8

104 SANGAKKARA and BlELER

Table 3. Effect ofmerit

Depthof planting (cm)

MI 4

02468Sx

Selection 7715

02468Sx

seed size a

Normal

14.592.572.4

14,6

0.00.7

18.7

94.3

46.7

15.3

0.00.7

ind planting depth

Small seedsAbnormal

22.30.0

22.532.14.5

1.2

16.5

1.2

28.3

53.7

2.71.7

Dead

63.2

7.5

5,1

53.3

95.53.9

64.84.5

25.041.0

97.3

3.7

on seedling emergence in mungbean 16

Number of seedlings

Medium seedsNormal Abnormal Dead

12.4

94.0

86.9

28.7

4.6

0.6

10.397.4

56.1

10.3

0,01.7

14.6

I.O

5.1

36.1

52,3

3.7

18,3

0.011.4

36.9

20,8

4.2

73.0

5.0

8.0

35,2

43.1

4.1

71.4

2.6

32.5

52.8

79.25.7

days after establish-

Large seedsNormal Abnormal

6.1

96.591.4

59.4

24.0

4.8

7,595.684.7

26.1

0.00.4

21.0

0.0

2.3

26.355.4

0.6

9.3

1.0

8.6

34.842.3

3.2

Dead

72.9

3.56.3

14.3

20.6

1.8

83.2

3.4

6.739,1

57,7

2.8

This procedure was adopted for all varieties andreplicated six times. The experimental design was acompletely randomized design, and the experimentwas repeated to consolidate results.

Measurements

Seedling emergence was observed in all categories ofseed at two day intervals. The seed rows were care-fully traced, the sand washed and seedlings of eachcategory divided into normal, abnormal and deadseedlings based on ISTA (1976) recommendations, at16 days after establishment.

Results and Discussion

Seedling emergence of cowpea and mungbeanwere affected by planting depth and seed size.At all depths of planting, larger seeds wereobserved to be early germmators, which assuggested by BREMNER et al. (1963) could beconsidered a resultant feature of a larger endo-sperm providing a greater food reserve to thegrowing embryo. However, seeds of bothspecies which were not covered showed poorgermination when compared to the other treat-ments.

The effects of planting depth and seed sizeon seedling types in cowpea and mungbean arepresented in Tables 2 and 3 respectively. Both

species showed similar trends in terms ofeffects of seed size and planting depth on seed-ling growth.

Normal seedlmg growth of both species wasdepressed when seeds were not covered withsand. In addition, smaller seeds showed betterseedling growth both within and betweenspecies in this treatment. For example, thelargest seeds amongst the four selected varieties(Cowpea selection TV X 193398) did not showany seedling growth when compared to thesmallest seeds in mungbean selection 7715.This indicates that the selected legumes needsome soil cover for germination and seedlinggrowth, and that larger seeds are more suscep-tible to the lack of a soil cover than small seeds.

Seedling growth of small seeded varieties isbest (indicated by a higher number of normalseedlings) when planted at a depth of 2 cms.The beneficial effect of planting depthincreases with seed size upto a depth of 6 cms,as shown by the large seeds of cowpea selec-tion TV X 193398. This suggests that largerseeds show better seedling growth withincreasing planting depth, upto an optimalvalue of the latter. Normal seedling growthdeclines reapidly when seeds are established atdepths greater than 4 cms for small seeds and6 cms for larger seeds. The number of abnor-

Seedling Growth of Cowpea and Mungbean as Affected by Seed Size and Seeding Depth 105

mal seedlings which indicate the germinationof the seed but its inability or difficulty topenetrate the top soil layer increases withplanting depth after 4 cms and 6 cms for smalland large seeds respectively. The percentage ofdead seedlings also increases with plantingdepth after an optimal value, even with the useof seeds with a high germinability.

Depth of sowing is often critical for success-ful seedling emergence (PERRY 1976). The datapresented also shows the presence of optimalplanting depth for the selected legumes, as athick layer overlying the seed acts as a mechan-ical barrier which affects seedling growth.Thus large seeded species and varieties prefer adeeper planting depth upto an optimal value,as depths beyond 6 cms affects seedlingdevelopment.

Seed size within a variety or species is adeterministic feature of the depth of planting.Using seeds of different sizes when estab-lishing a crop at a given depth therefore resultsin poor seedling establishment. Therefore, thesuccessful establishment of a crop, especiallyby direct seeding requires both uniform seedmaterial and a uniform planting depth toobtain good seedling growth. Nonuniformseed placement (either at the surface or toodeep) of nonuniform seed material results inpoor emergence and a greater number of deador abnormal seedlings which are of no value inagricultural production.

Zusammenfassung

Samlingswachstum der Augenbohne undMungbohne in Abhangigkeit von der Sa-mengrofie und der Aussaattiefe

Keimung und Samlingswachstum von unter-schiedlich grofien Samen der Augenbohne undMungbohne wurden in Abhangigkeit von ver-schiedenen Aussaattiefen mit der modifiziertenHiLTNER-Methode beobachtet. Alle Samen, diean der Oberflache lagen, zeigten schwachesSamlingswachstum, allerdings waren kleine Sa-men weniger empfindlich als groiSe. Das Sam-lingswachstum von kleinen Samen nahm raschab bei einer Aussaatciefe von 4 cm und mehr,wahrend grofSe Samen vergleichbarc Ergeb-

nisse bei Aussaattiefen von 6 cm zeigten. DerWert einer gleichmafSigen Samengrofie undAussaat in gleicher Tiefe wird dargelegt.

Acknowledgements

The authors wish to record with appreciation theassistance rendered by Mr. E. R. PlYADASA of theDepartment of Crop Science.

References

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