Seed germination, seedling growth and biomass production of eight Central-American multipurpose trees under nursery conditions in Zomba, Malawi

Forest Ecology and Management, 27 (1989) 21-27

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Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands

Seed Germination, Seedling Growth and Biomass Production of Eight Central-American Multipurpose Trees under Nursery Conditions in Zomba, Malawi MZOMA R. NGULUBE

Forestry Research Institute of Malawi, P.O. Box 270, Zomba, Malawi (Accepted 18 May 1988)

ABSTRACT

Ngulube, M.R., 1989. Seed germination, seedling growth and biomass production of eight CentralAmerican multipurpose trees under nursery conditions in Zomba, Malawi. For Ecol. Manage, 27: 21-27. Seeds of eight dry-zone multipurpose tree species from Central America were treated using six different treatments before sowing in the nursery. All species achieved high germination percentages within 21 days in the nursery after scarification and boiling-water treatments. Caesalpinia criostachys, Crescentia alata and Gliricidia sepium also achieved high germination without any treatment, but Caesalpinia velutina and Senna atomaria required the use of sulphuric acid. Once germinated, seedling growth in the nursery varied highly between species, with Gliricidia sepium, Enterolobium cyclocarpum and Albizia guachepele showing faster height growth than the rest. On the basis of height growth alone, the remaining five species (Caesalpinia eriostachys, Caesalpinia vehttina, Crescentia alata, Guazuma ulmifolia, and Senna atomaria ) would require at least 3 months in the nursery to attain the current recommended 20-cm height for field-planting of nursery stock in southern Africa.

INTRODUCTION

The steady increase in demand for fuelwood as the traditional and most economic source of energy in Malawi has dictated a need for establishment of fuelwood plantations and communal villagewoodiots throughout the country, especially in the heavily populated dry areas where wood shortage is critical. Eucalyptus camaldulensis and E. tereticornis, recommended for such programmes (Nkaonja, 1985) are widely accepted for use in periurban fuelwood plantations and communal woodlots. However, successful establishment of the eucalypts not only involves large-cost outlays for fertilizers (NPK and Borate) and insecticides (Aldrin), but also requires intensive silviculture. Considering 0378-1127/89/$03.50

© 1989 Elsevier Science Publishers BN.

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the financial limitations in rural areas, and with the lesser attention given to trees than to the food crops, the eucalypts may not be the best-suited species for integration into small-scale farming systems. As population pressure continues to force agricultural expansion (including cropping and grazing) into more marginal areas, it becomes more urgent to identify and test other fast-growing species capable of providing the smallholder farmer with multiple benefits. Such benefits should include small-diameter fuelwood and poles, dry-season forage, shade and shelter. The species chosen for such purposes should be capable of being inexpensively established and of integrating well with food crops. In 1984, seed of dry-zone multipurpose trees indigenous to Central America, and neighbouring regions of Southern America, were offered by the Oxford Forestry Institute (OFI) for trials. These species mainly consisted of nonindustrial species, some of them little known botanically (Hughes and Styles, 1984). Seed pretreatments and nursery management of these species had to be developed. This paper presents results of such a study involving eight species included in our field trials in Malawi. MATERIALS AND METHODS

The study was conducted at the Forestry Research Institute of Malawi (FRIM) nursery (35 ° 19'E, 15 ° 26'S) 1100 m above sea level in Zomba DisTABLE 1 List of multipurpose species a n d details of t h e i r seed sources Species

Albizia guachepele Caesalpinia eriostachys Caesalpinia velutina Crescentia alata Enterolobium cyclocarpum Gliricidia sepium Guazurna ulrnifolia Senna atornaria

N *

9 -24 25 14 87 25 30

*Number of p a r e n t trees

Locality Motagua, Guatemala Choluteca, Hondurus El Rancho, Guatemala Comayagua, Hondurus Otoro, Hondurus Laguna Tecomapa La Trinidad, Nicaragua Comayagua, Hondurus

Latitude

Longitude

Altitude (m)

15 ° 59' N

89 ° 40' W

200

13 ° 23' N

87 ° 0 7 ' W

100-160

14 ° 57' N

90 ° 01' W

250

14 ° 14' N

87 ° 36' W

700

14 ° 28' N

88 ° 00' W

600- 700

12 ° 37' N

86 °03' W

380

12°59'N

86°15'W

550

14°22'N

87°39'W

600-700

23 trict. T h e area experiences a m ean annual rainfall of 1500 m m and a m e a n annual t e m p e r a t u r e of 23 ° C. T h e eight species involved in t he e x p e r i m e n t and details of t hei r seed origins are given in Table 1.

Germination of treated seeds Six treatments including a control were applied to evaluate their effectiveness on seed germination of the eight species under nursery conditions in Zomba. The treatments were as follows:control (seeds sown without any treatment); moderate acid immersion (30 seeds immersed in 50 ml* of sulphuric acid, 98% assay for 10 rain); extended acid immersion (as for moderate acid, but for 20 rain);boiling water (pouring 30 seeds into boiling water which had been removed from the heat source for 30 seconds, then the water was decanted and replaced by tap water and the seeds were soaked overnight); hot water (30 seeds in a container having 50 ml* of 100 °C hot water and leftin water as it cooled overnight); and mechanical hand-scarification (seeds were scratched individuallyusing medium-grade sandpaper). A randomized complete-block experimental design with three-fold replication was used. Each treatment consisted of 30 sound, well-filledseeds (10 seeds per replication) directlysown into black polythene tubes (10-cm 'layflat',15 c m deep) containing a potting mixture of 70% forestsoiland 30% dambo sand. The seeds were sown at a depth of 0.5-1.5 cm. Watering was done morning and evening for 21 days, during which germination counts were made daily. Germination was considered to be the emergence of the cotyledons above the soil surface. A bamboo shed set up for the period of the experiment prevented exposure to direct insolation.The resultswere analysed (afterarcsine transformation of germination percentages ) using Analysis of Variance ( A N O V A ) and Duncan's multiple range tests.

Seedling growth and biomass production Using the germination resultsof the treated seeds,boilingwater was applied as a seed treatment for all eight species. One hundred and fiftyseeds of each species were sown directlyinto black polythene tubes (same size and potting mixtures as in the earlier experiment) arranged in separate blocks. Nursery conditions during germination were the same as described previously.All seeds germinated well within 21 days, afterwhich the bamboo shed was removed and the seedlingsarranged in a randomized experimental block design. Each treatment consisted of 25 seedlings per block, with a three-foldreplication.Watering continued as before. Weeds were removed on detection and root-pruning was done whenever roots penetrated the nursery bed soil. "100 ml was used for Enterolobiumcyclocarpumseeds because of their large size.

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Measurements were taken at 1, 2 and 3 months after germination. On each occasion height (cm) and diameter (ram) close to the soil surface were measured using a 100-cm ruler and a micro-calliper, respectively. At the end of the 3 months, 10 seedlings of each species were randomly selected. The seedlings were cut near the soil surface; the shoot and root systems were separated and oven-dried at 70°C for 24 h, after which shoot and root dry-weights were recorded. Root : shoot ratios were based on dry-weight. The results were analysed using ANOVA and Duncan's multiple range tests. RESULTS A N D DISCUSSION

Germination of treated seed M e a n total germination 21 days after sowing is summarized in Table 2 for each species and treatment. Table 2 shows that more than 70% germination could be achieved with scarificationand boiling-water treatments for all species. Caesalpina eriostachys, Crescentia alata and Gliricidia sepium achieved 100, 93, and 85% germination, respectively, without any treatment. For the remaining species, the extent of improvement of scarification and boiling-water treatments (over 21 days) over untreated seed makes it clear that these treatTABLE 2 Mean germination percentage by 21 days after sowing in the Zomba nursery, 1986 Species

Albizia guachepele Caesalpinia eriostachys Caesalpinia velutina crescentia alata Enterolobiurn cyclocarpum Gliricidia sepium Guazuma ulrnifolia Senna atornaria

Control

H2804

Water

10 min

20 rain

60c

63c

83c

40d

100a

100a

70b

67b

100a

20c

100a

40c

100a

100a

100a

57b

100a

93a

0e

0e

83c

30d

87b

0a

37d

53c

93b

27e

100a

85b

47d

30e

87b

30e

100a

0d

43b

33c

77a

0d

73a

0c

100a

100a

97a

47b

100a

0e*

Boiling

Scarification Hot

*Values in the same row with the same letter do not differ significantly (P < 0.05).

25 ments are major requirements in nursery practice for achieving uniform, swift and high germination. Both methods are suitable for rural use since neither sophisticated equipment nor techniques are required for their use. Scarification is sometimes laborious, and its applicability is thus limited to small samples; however, a rotating drum bringing the seeds into contact with sharp gravel can be used to treat s e e ~ in bulk. If this equipment is not available, boiling water can be used but the method does have the disadvantage of making seeds wet and swollen and difficult to handle (Doran et al., 1983). Although sulphuric acid was effective with Cae. velutina and Senna atomaria (100% in both cases), its applicability to rural situations is questionable. Sulphuric-acid treatment requires resistant containers and presents a risk to both the operator and the seeds. The ineffectiveness of the method with the other species may be related to treatment duration. The 10-rain treatment may be too short for effective corrosion of the seed coats, whereas the 20-rain treatment may have damaged the tissues within the coat. The depressed germination with hot water emphasizes how critical it is to use an appropriate treatment. Although Anonymous (1980) recommends hot water pretreatment for Gl. sepium, the method failed to achieve successful germination with Gl. sepium in the present study. However, it should be noted that the effectiveness of hotwater treatment depends on the seed : water-volume ratio and the ambient temperature, because these influence the total amount of heat the seeds are exposed to over the soaking period. Indeed the failure of this method in the study may have resulted from the 'cooking' of seeds due to the excessive heat.

Height and diameter growth Seedling height varied significantly (P < 0.01 ) among the species at all ages, although the ranking of the species fluctuated with age (Table 3). The high initial growth of Enterolobium cyclocarpum is undoubtedly due to the large seed which has abundant food reserves to support the young plant and allow it time to establish. Apart from Gl. sepium which ranked highest at ages 2 and 3 months, En. cyclocarpum ranked higher than the rest throughout. The initial high growth of Cae.salpinia eriostachys and Cae. velutina, however, completely disappeared with age, whereas Albizia guachepele and Cr. alata, which had shorter seedlings initially, ranked among the highest at the end of the 3-month period. The data in Table 3 also show high variability within species as indicated by standard deviations. Such within-species variability might later be exploited in selective tree improvement work. Diameter growth, as for height, varied significantly ( P < 0.01 ) at all ages, but with little fluctuation as regards ranking with age (Table 3). Gliricidia sepium and En. cyclocarpum, which ranked high in height growth, also ranked high in diameter throughout the study period. Guazuma ulmifolia ranked lowest in diameter throughout the experiment, possibly due to the fact that Gu. ulmifolia has smaller seeds than the other species involved

26 TABLE 3 Mean heights and diameters of multipurpose dry-zone hardwood species at ages 1, 2 and 3 months in the Zomba nursery, 1986 Specoes

Height (cm) i month

Albiziaguachepele 8.6(0.3)cd* Caesalpiniaeriostachys 12.5(0.6)b Caesalpiniavelutina 9.6(0.4)c Crescentiaalata 7.4(0.6)cd Enterolobiumcyclocarpurn 15.7(1.3)a Gliricidiasepium ll.6(0.1)b Guazumaulmifolia 4.5 (1.2)e Sennaatomaria 7.6(0.6)cd

Diameter (mm) 2 months

3 months

1 ~nonth

2 months

3 months

12.2(0.8)d 13.6(0.6)c 10.2(0.5)f 10.3(0.8)f 17.0(1.1)b 18.0(0.4)a 7.7 (0.7g 11.3(0.7)e

21.6(1.2)c 16.9(0.8)e 10.9(0.2)f 18.9(1.3)d 24.9(1.4)b 37.8(2.4)a 10.3(1.1)f 18.7(1.2)d

1.3(0.2)d 2.3(0.3)bc 2.0(0.1)cd 2.8(0.2)bc 3.5(0.4)b 4.5(0.4)a 1.1 (0.1)d 1.7(0.3)cd

2.2(0.3)cd 2.7(0.2)bc 2.4(0.2)cd 3.3(0.4)bc 3.9(0.4)b 5.5(0.5)a 1.8(0.1)d 2.6(0.2)bc

3.3(0.1)bc 3.2(0.1)bc 2.5(0.3)bcd 3.9(0.4)bc 4.7(0.3)b 7.1(0.4)a 1.9(0.1 )d 3.2(0.3)bc

*Means in the same column with the same letter(s) do not differ significantly at P < 0.01 (figures in brackets are standard deviations ). TABLE 4 M e a n total dry-weight and root: shoot ratio of multipurpose dry-zone hardwood species at age 3 months in the Z o m b a nursery, 1986 Species

Dry-weight (g)

Root: Shoot ratio

Albizia guachepele Caesalpina eriostachys Caesalpinia velutina Crescentia alata Enterolobium cyclocarpum Gliricidia sepium Guazuma uliifolia Senna atomaria

7.7 ( 1.2 )c* 5.7 (1.5) d 1.5 (0.8) f 7.9 (1.6)c 12.2 (3.1) b 31.4 (6.2) a 2.6 ( 0.7 ) e 5.9 ( 2.2 ) d

0.56ab 0.84a 0.47c 0.78b 0.52b 0.28e 0.45c 0.38d

*Means in the same column with the same letter (s) do not differ significantly at P < 0.01 (figures in brackets are standard deviations ).

in the study. There was highly positive relationship between seedling height and diameter ( r > 0.70 in all species), which might make it possible to select for either or both characters together in a selection programme.

Biomass Total dry-weight and root : shoot ratio varied significantly ( P < 0.01) between species (Table 4). The higher biomass production in G/.sepium followed by En. cyclocarpum, Cr. alata and A. guachepele is a reflection of the higher growth rates as shown in Table 3. However, the variability within each species was high, as evident from the standard deviations. During the destructive sampling, nodules were noted in A. guachepele, En. cyclocarpum and Gl. sepium.

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The ability of these species to nodulate is important in soil fertility and plant growth, as it is within the nodules where bacteria convert nitrogen gas from the air into soluble compounds for plant use (Anonymous, 1983). The nodulation ability of the above-mentioned species probably contributed to the good growth of their seedlings (Table 3) in the nursery. The variation of biomass between the species may also be related to their growth habit and general morphology. Gliricidia sepium seedlings, unlike the other species in this study, have abundant numbers of broad leaves, reflected in the low root : shoot ratio (Table 4) achieved compared to the other species. The high root : shoot ratio in Cae. eriostachys compensates for the inferior growth ability of the species. However, whether the root : shoot ratio in these species is critical in early field survival and subsequent growth is not known at present. ACKNOWLEDGEMENTS

I wish to thank the Oxford Forestry Institute for providing the seeds for the study, and the International Development Research Centre (IDRC) of Canada for financially supporting the study under the Rural Fuelwood and Polewood Research Project in Malawi.

REFERENCES Firewood Academy Press, Firewood crops: shrub and tree species for energy production. Anonymous, 1980. National Academy of Sciences, National Academy Press, Washington DC, 237 pp. Anonymous, 1983. Mangium and other acacias of humid tropics.National Academy of Sciences, National Academy Press, Washington, DC, 62 pp. Doran, J.C.,Turnbull, D.J. and Gunn, B.V., 1983. Handbook on Seeds of Dry-Zone Acacias. FAO, Rome. Hughes, C.E. and Styles, B.T., 1984. Exploration and seed collectionof multi-purpose dry zone trees in Central America. Int. Tree Crops J., 3: 1-31. Nkaonja, R.W.S., 1985. Fuelwood and polewood research project for the rural population of Malawi. For. Res. Rec. No. 62, 83 pp.