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Effects of site preparation and fertilizer application at planting on Eucalyptus tereticornis at Morogoro, Tanzania
Forest Ecology and Management, 18 (1987) 103-112
103
Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands
E f f e c t s of S i t e P r e p a r a t i o n and F e r t i l i z e r A p p l i c a t i o n at P l a n t i n g on Eucalyptus tereticornis at M o r o g o r o , T a n z a n i a S.A.O. CHAMSHAMA and JOHN B. HALL*
Division of Forestry, University of Dares Salaam, Morogoro (Tanzania) *Present address: Department of Forestry and Wood Science, University College of North Wales, Bangor, Gwynedd LL57 2UW (Great Britain) (Accepted 28 July 1986)
ABSTRACT Chamshama, S.A.O. and Hall, J.B., 1987. Effects of site preparation and fertilizer application at planting on Eucalyptus tereticornis at Morogoro, Tanzania. For. Ecol. Manage., 18: 103-112. Uniform nursery stocks of Eucalyptus tereticornis were used to establish an experiment factorially combining site preparation (three levels - - bedding; disking; neither bedding nor disking), initial nitrogen applications (two levels - - 75 g ammonium sulphate per plant; 0 g ammonium sulphate per plant) and initial phosphorus applications (150 g triple super phosphate per plant; 0 g triple super phosphate per plant). Monitoring was carried out for 2 years by which time trees were up to 3.2 m tall and 5.0 cm in diameter at the root collar. Survival at 2 years was significantly higher among plants that had received nitrogen (65%) than those which had not (53%) and among plants on disked or bedded sites (62%) than those on unworked soil (53%). Monthly height increment was briefly, but significantly, increased in plants supplied with additional nitrogen and further enhanced if there was also additional phosphorus. Monthly diameter increment was, over most of the 1st year, significantly greater on sites prepared by bedding; significant increases also resulted, though for more restricted periods, from site preparation by disking and from provision of additional nitrogen. At the end of I year significantlyhigher concentrations of foliar potassium, suggesting enhanced drought hardiness, were detected for plants on bedded or disked ground. The concentration in these was 1%; on unworked ground the corresponding value was 0.8%. Combining bedding or disking with an initial application of nitrogen offset this effect, The short period over which growth benefits from the site preparation and nitrogen application treatments is noted but it is stressed that initial growth encouragement is desirable with Eucalyptus and that overall benefits, as in improved survival, may be long term. The value of phosphorus applications under the prevailing conditions is considered unproven.
INTRODUCTION In the 1950's forest p l a n t a t i o n s in T a n z a n i a a n d other E a s t A f r i c a n count r i e s w e r e m a i n l y e s t a b l i s h e d i n m o n t a n e a r e a s w h e r e soils a r e c o m p a r a t i v e l y
0378-1127/87/$03.50
© 1987 Elsevier Science Publishers B.V.
104 fertile and water stress problems relatively infrequent. This, added to the fact that there was clean weeding through the taungya system used in raising plantations, generally resulted in good survival and growth of seedlings. Montane forests, however, are no longer cleared for plantation forestry. Instead, plantations are being extended to much drier areas - - often with relatively infertile soils. Forestry's traditional preoccupation with wood production on a national basis has limited local effort towards identifying species of afforestation value for dry areas. Advantage was taken of experience elsewhere with Azadirachta indica A. Juss., Cassia siamea Lain., Eucalyptus camaldulensis Dehnh. and E. tereticornis Sm. once the urgency for forestry to combat increasing fuelwood deficits in the Tanzanian hinterland was appreciated. Until there is more familiarity with indigenous alternatives and additional exotic species, these four are likely to remain the nucleus of the country's dry-area afforestation options. The remarkable form and growth rate in Tanzania of the Eucalyptus designated 'Zanzibar C' and interpreted (FAO, 1981 ) as a hybrid between the two species mentioned above has stimulated particular interest in E. tereticornis. Although E. tereticornis is the least hardy (Tanzania Forest Division, 1984 ) of the four species named, excellent form and impressive growth account for its popularity wherever conditions are suitable. Conditions at Morogoro favour E. tereticornis and it was therefore considered appropriate for this study. Successful afforestation in these areas requires drought-hardened seedlings of species which can survive long periods of water shortage and requires an improved microsite environment created by appropriate regimes of site preparation and fertilization, combined effectively. This study examines the effect of different site preparation techniques and applications of nitrogen and phosphorus on 2 years survival and growth of E. tereticornis. MATERIALSAND METHODS Study area The study was conducted at the University ofDar es Salaam Forestry Experimental Area at Mafiga, Morogoro, Tanzania (6 ° 50' S, 37 ° 38'E; 500 m). Mean annual rainfall (1976-83) is 733 mm; mean annual temperature is 24.5°C. Soils are fine loamy sands. Further site characteristics are given by Lulandala (1978), Chamshama (1984) and Chamshama and Hall (1984). Information on seed source and nursery procedures adopted is reported by Chamshama and Hall (1984). Experimental design A three-factor fixed effects factorial model was adopted to study the effects of three site-preparation treatments (control, bed and disk), two levels of N
105 fertilizer (0 g and 75 g a m m o n i u m sulphate per plant) and two levels of P fertilizer (0 g and 150 g triple superphosphate per plant). The twelve treatments were each represented once in each of four replicate blocks.
Initiation and maintenance of experiment Before treatments were imposed, soil samples were taken from block centres for the depth range 0-30 cm. Site preparation was carried out in February 1981. The control t r e a t m e n t involved chopping of the vegetation: no further site preparation accompanied this. A single gang harrow pulled by a tractor was used to prepare the beds of the bed treatment, ridges 15-20 cm high being formed by making two passes of the harrow and rolling the soil towards the middle of the strip. The disk (complete cultivation) t r e a t m e n t consisted of ploughing, harrowing and disking to a depth of about 20 cm. Seedlings were planted manually in March 1981. Planting espacement was 2.5 × 2.5 m, and 49 seedling were planted in each replicate of each treatment. In the bed t r e a t m e n t seedlings were planted in the centre of the ridges. Fertilizers were applied 1 day after planting out as a 15-cm radius ring around each seedling treated. Complete manual weeding was carried out at intervals of about 3 months for 2 years.
Monitoring and sampling procedures At ages of 1, 3, 6, 12, 18 and 24 months, assessments of the inner 25 plants per replicate per t r e a t m e n t were made, for survival, height and root collar diameter at points marked 2 cm above the soil surface at the time of planting. Foliar samples were collected for nutrient analysis from a random sample of two plants per replicate per t r e a t m e n t at 12 months and 24 months after planting. Leaves were collected from the upper one-third of the crowns of sampled trees. Fully developed leaves in the outer part of a branch, taken at random, composed the sample. Soil samples from the 0-30 cm depth range were twice collected from the centre of each replicate of each t r e a t m e n t - - 12 months and 24 months after planting.
Laboratory procedures Foliar samples were carefully washed with distilled water to remove dust, then air dried, placed in paper bags and oven-dried at 70 ° C for 72 h. After oven drying, samples were ground in a Christy and Norris mill. Total N was determined by the macro-Kjeldahl procedure. For the determination of other nutrients, ground samples were ashed at 450 ° C in a muffle furnace for 3 h and the ash digested in 6 N hydrochloric acid. Aliquots of the solution were used to
106
determine P colorimetrically and K, Ca and Mg by using an atomic absorption spectrophotometer. Soil samples were oven dried at 70 °C for 72 h and sieved to pass through a 60-mesh sieve. The following determinations were made: exchangeable K, Ca and Mg; available P; and total N. Exchangeable cations were leached from the soil using neutral 1N ammonium acetate and individual cation concentrations were estimated by atomic absorption spectrophotometry. Phosphorus was extracted by the Bray and Kurtz method number 1 (Bray and Kurtz, 1945) and the concentration estimated colorimetrically by the blue molybdenum method. Nitrogen was estimated by the macro-Kjeldahl technique.
Statistical analyses All data were subjected to analyses of variance. Percentage figures were transformed (angular transformation) before analysis of variance was done. Differences associated with different levels of a factor were examined by use of orthogonal contrasts. RESULTS
Seedlings 30 cm tall were planted in the field. At the end of the 24-month observation period the trees monitored in this study ranged from 2.59 m to 3.24 m in height and from 3.85 cm to 5.02 cm in root collar diameter (Table 1). TABLE 1 Mean heights (m, upper figures), mean root collar diameter (cm, middle figures) and survival (%, lower figures) ofE. tereticornis after 24 months in the field at Morogoro, Tanzania Site preparation
Neither bedding nor disking Disking not bedding Bedding not disking
Initial fertilizer application (per plant) No fertilizer
Ammonium sulphate (75 g) only
Triple super phosphate (150 g) only
Ammonium sulphate (75 g) and triple super phosphate (150 g)
2.79 4.13 56 2.72 4.36 56 2.94 4.84 51
3.12 4.54 55 2.95 4.65 69 3.02 5.02 65
2.78 4.40 36 2.59 3.85 59 3.00 4.92 58
3.24 5.02 64 3.02 4.33 66 2.84 4.60 72
107 TABLE 2 Significant effects on E. tereticornis survival of initial applications of nitrogen fertilizer (75 g ammonium sulphate per plant) and bed and disked site preparation treatments at Morogoro, Tanzania Assessment age (months)
Factor significant
Contrasting factor levels and mean survival ( % )
12
nitrogen fertilization (P < 0.001 ) site preparation (P < 0.05 ) nitrogen fertilization (P < 0.001 ) nitrogen fertilization ( P < 0.001) site preparation ( P < 0.05 )
fertilization (68.8), no fertilization (58.2) bedding/disking (66.3), no bedding/disking ( 58.0 ) fertilization (66.3), no fertilization ( 54.2 ) fertilization {65.1 ) no fertilization (52.7) bedding/disking (62.0), no bedding/disking (52.8)
12 18 24 24
TABLE 3 Significant direct effects on E. tereticornis height (cm month-~) and diameter (mm month ~) increments of initial applications of nitrogen fertilizer (75 g ammonium sulphate per plant) and bed and disked site preparation treatments at Morogoro, Tanzania Assessment period ( months since planting)
Increment parameter
Factor significant
Contrasting factor levels and mean increments
2-3
height
2-3
diameter
2-3
diameter
4-6
diameter
4-6
diameter
7-12
diameter
nitrogen fertilization (P<0.001) nitrogen fertilization ( P < 0.001 ) site preparation (P < 0.01 ) nitrogen fertilization ( P < 0.001 ) site preparation (P<0.05) site preparation (P < 0.05 )
fertilization (8.4), no fertilization (15.0) fertilization (2.57), no fertilization (1.75) bed ( 2.45 ) ; disked ( 2.05 ), no bedding/disking (1.98) fertilization (1.51), no fertilization (1.03) bed (1.50), disking and no bedding/disking {1.15) bed (1.80), disking and no bedding/disking (1.40)
Survival percentage was found to reflect ( Table 2 ) the treatments applied but o n l y at t h e late a s s e s s m e n t s (12, 18 a n d 24 m o n t h s ) . T h e f a c t o r s i n v o l v e d w e r e N f e r t i l i z a t i o n a n d site p r e p a r a t i o n ; n o s u r v i v a l d i f f e r e n c e s w e r e a s s o c i a t e d with P fertilization. No interactions between factors influenced survival. Survival was highly significantly enhanced by N fertilization, the advantage subsequently persisting. Site preparation had a positive but comparatively weak
108 TABLE 4 Effects on height increment (cm m o n t h 1) of E. tereticornis in the 2nd and 3rd month in the field of initial applications of nitrogen fertilizer (75 g ammonium sulphate per plant) and phosphorus fertilizer (150 g triple super phosphate per plant) at Morogoro, Tanzania Phosphorus fertilizer
Nitrogen fertilizer
not applied applied
not applied
applied
8.75 13.97
8.03 16.09
Least significant difference (P~-0.05): 3.38. TABLE 5 Effects of foliar potassium concentration (%) of E. tereticornis after 12 months in the field of initial application of nitrogen fertilizer ( 75 g ammonium sulphate per plant) and bed and disked site preparation treatments at Morogoro, Tanzania Nitrogen fertilizer
Site preparation treatments
bedding disking neither bedding nor disking
applied
not applied
0.97 1.06 0.82
1.19 0.83 0.86
Least significant difference {P = 0.05 ) : 0.31. TABLE 6 Effects on foliar potassium concentration (%) of E. tereticornis after 12 months in the field of initial applications of nitrogen fertilizer (75 g ammonium sulphate per plant) and phosphorus fertilizer {150 g triple super phosphate per plant) at Morogoro, Tanzania Phosphorus fertilizer
Nitrogen fertilizer
applied not applied
applied
not applied
1.04 0.86
0.90 1.00
Least significant difference (P=0.05) : 0.17. effect, s i g n i f i c a n t o n l y f o r t h e r a i n y s e a s o n a s s e s s m e n t s (12 a n d 24 m o n t h s ) . N o s i g n i f i c a n t s u r v i v a l d i f f e r e n c e s w e r e a s s o c i a t e d w i t h t h e d i f f e r e n t site p r e p aration methods used. Height increments were found to reflect N and P fertilization only during
109 TABLE 7 Nutrient concentrations in the soil for depth range 0-30 cm at Mafiga, Morogoro, Tanzania prior and subsequent to site preparation by bed and disking treatments Nutrient
Total nitrogen (%) Available phosphorus (ppm) Exchangeable potassium (meq per 100 g) Exchangeable calcium (meq per 100 g) Exchangeable magnesium (meq per 100 g)
Concentration after 24 months Prior to treatment
Following bedding
Following disking
0.04
0.04
0.05
8.80
8.91
8.77
0.74
0.61
0.72
8.46
8.45
8.30
1.34
1.04
0.95
the second and third months in the field (the height of the 1981 rainy season). Nitrogen fertilization accelerated height growth (Table 3) both as a direct effect and through an interaction with P fertilization (Table 4). Phosphorus fertilization had no direct effect on height increment. Neither direct nor interaction effects of site preparation on height increment were revealed. Diameter increments were significantly influenced (Table 3 ) during the last three of the four assessment intervals consituting the 1st year in the field, by treatments applied. Nitrogen fertilization accelerated diameter growth from the 2nd to the 6th month in the field during which time soil moisture tension remained moderate ( < - 4 bar). Site preparation promoted diameter growth from the 2nd month to the 12th; initially, bed treatments induced significantly faster growth than disking which, in turn, induced significantly faster growth than control conditions. From months 4-12, however, the advantage of disked over control treatments disappeared while the bed treatment remained significantly superior to both. At no stage was there any significant effect on diameter increment of P fertilization or interactions between factors. After 12 months, no significant effects on diameter increments were found with any treatment. There was evidence only for the 12-month samples that treatments applied influenced foliar nutrient concentrations and then only in the case of K. All factors exerted influence on foliar K concentration through interaction effects but only with site preparation was there also a direct effect. Foliar K concentration for trees planted where there had been no bedding or disking was significantly ( P < 0.05 ) lower ( 0.84% ) than for trees planted on ground prepared by either bedding or disking (combined mean, 1.01% ). The significant inter-
110
action effects were of site preparation with N fertilization (Table 5 ) and of N fertilization with P fertilization (Table 6). Soil nutrient levels ( Table 7 ) did not change significantly during the period of study. DISCUSSION
If both are beneficial, it is logical to combine site preparation operations with fertilizer applications to improve seedling survival and growth prospects during the sensitive period after planting. Experimental studies mostly look at these factors separately, however. No studies in the drier parts of East Africa have considered interactions of fertilizer applications and site preparation as they affect Eucalyptus performance, although Solberg and Lysholm (1979) report use of this approach with Pinus caribaea Morelet. Determination to extend planting into the drier areas of Tanzania in the coming years to counter trends of diminishing fuel supply warrants attention to this topic since seed availability, silvicultural familiarity, rapid growth potential and suitability for fuel indicate that Eucalyptus spp. will be used very widely. Indications ( Chingaipe, 1985) that Eucalyptus can approach or reach its potential only when appropriate management is applied from the earliest stage underline the importance of sound initial establishment-promoting procedures. This study has demonstrated that under Morogoro conditions effects of both fertilization and site preparation are reflected in the early growth ofE. tereticornis and that interactions involving fertilizer applications and site preparation arise. A brief (1 or 2 months) lag ensued between planting and response to experimental treatments, presumably because initially plants depended on the soil balls inherited from the tubes used for nursery propagation. Thereafter, positive effects from site preparation and fertilizer applications were expressed as enhanced increment until the end of the first 12 months. The most persistent benefit was from site preparation but, of the two preparatory measures taken, only the bed treatment led to accelerated diameter growth after the 3rd month. The site conditions in the experimental area are such that the benefits of bedding are probably from concentration in the ridges of humus, litter and topsoil leading to more available nutrients and allowing more moisture retention and a longer period of moisture availability than in unprepared soil. The earlier (after only 6 months) cessation of benefits from N fertilization suggests that by the time the rainy season ends any available N additional to that normally present at the site has disappeared - - perhaps through leaching in the rainy season or mineralisation as the soil dries out. The shorter annual period of vigorous height growth typical of woody plants in strongly seasonal climates ( Hopkins, 1970 ) explains the short-lived expression of the height increment enhancement associated with the initial application of N. The apparent loss of extra N before the next growing season would
111
account for the absence of a similar response in 1982. The involvement of P in a beneficial interaction with N is a situation reported elsewhere ( Cromer, 1971 ). Here, the absence of direct effects, the restriction of significance to a single set of height increment data and the marginal level of significance all suggest a chance result; lack of response of Eucalyptus to P application has been noted often and McKimm and Flinn {1979) surmise that members of the genus, having evolved on P-poor soils, require less of the element than do most other plants. For the other parameters examined, the significant responses noted refer to cumulative effects; though detectable in data collected from 12-24 months after planting, the benefits may have been conferred within the 1st year and persisted thereafter. Thus, if N fertilization ensured improved establishment and survival over the critical early period, by the time plants had been in the field for a year they would face less risk of mortality and the effect of the treatment would remain. Explanation of the effect on survival of site preparation is less straightforward. In contrast with effects on diameter growth, advantages of both preparatory treatments over unprepared soil persisted, perhaps because thorough destruction of pre-existing vegetation matters more for survival. The temporary interruption of this advantage revealed by the 1981/82 dry season assessment may indicate resumption of soil water recharge too late to benefit all individuals favoured earlier by site preparation activities. Enhancement of K uptake indicated by higher foliar concentrations 12 months after planting requires further investigation since no earlier checks were made. It is unclear why such a response should directly be promoted by both types of soil preparation or through interactions of site preparation effects with N fertilization. The effect, however, is considered beneficial - - higher K status signifies increased drought hardiness. The findings of this study should influence establishment practice for E. tereticornis in sandy soils in areas enjoying 600-800 mm mean annual rainfall. The brevity of periods when significantly faster growth occurred does not invalidate routine use of the treatments responsible; the benefits persist and their importance is real because Eucalyptus responds most positively to the earliest provision of favourable growing conditions. The key operation is site preparation by bedding, with its long period of growth promotion and its apparent increasing of drought-hardening. The better growth arising when there had been initial N fertilization might not be accompanied by a similar advantage if Eucalyptus reacts to this in the same way as softwood species ( Larsen, 1980 ) ; in combination with site preparation treatments this might counter any tendency towards enhanced drought hardiness. A choice may be necessary between emphasis on increased drought hardiness (avoid N fertilization on sites deemed risky) and accelerated growth (N fertilization appropriate on sites with predictable rainfall patterns). Routine P fertilization does not appear justified in view of its inconsistent
112 ( a n d n e v e r m a r k e d ) a s s o c i a t i o n w i t h s i g n i f i c a n t l y i n c r e a s e d g r o w t h a n d its a p p a r e n t lack of effect on survival. ACKNOWLEDGEMENTS T h e w o r k described was facilitated by f u n d i n g f r o m the N o r w e g i a n A g e n c y for I n t e r n a t i o n a l D e v e l o p m e n t as p a r t o f its S t a f f D e v e l o p m e n t P r o g r a m m e for t h e Division of F o r e s t r y , U n i v e r s i t y o f D a r es S a l a a m . We t h a n k t h e H e a d s a n d t h e t e c h n i c a l a n d n u r s e r y s t a f f of t h e U n i v e r s i t y ' s Division of F o r e s t r y a n d Soil Science D e p a r t m e n t for a s s i s t a n c e w i t h a n a l y s e s a n d e x e c u t i o n of r o u t i n e field m a i n t e n a n c e activities.
REFERENCES Bray, R.H. and Kurtz, L.T., 1945. Determination of total, organic and available forms of phosphorus in soils. Soil. Sci., 59: 39-45. Chamshama, S.A.O., 1984. Establishment techniques for Eucalyptus species: effects of nursery treatments, site preparation and fertilization on survival and growth. Ph.D. Thesis, University of Dares Salaam, Tanzania. Chamshama, S.A.O. and Hall, J.B., 1984. Height graded Eucalyptus tereticornis seedlings: one year field performance. For. Ecol. Manage., 7: 225-232. Chingaipe, T.M., 1985. Early growth of Eucalyptus camaldulensis under agroforestry conditions at Mafiga, Morogoro, Tanzania. For. Ecol. Manage., 11: 241-244. Cromer, R.N., 1971. Fertilizer trials in young plantations of eucalypts. Aust. For. Res., 5: 1-10. FAO, 1981. Eucalypts for Planting. FAO For. Ser. 11, Food and Agriculture Organization, Rome, 677 pp. Hopkins, B., 1970. Vegetation of the Olokemeji Forest Reserve, Nigeria. VII. The plants on the savanna site with special reference to their seasonal growth. J. Ecol., 58: 795-825. Larsen, J.B., 1980. Die Bedeutung der Nahrstoffversorgung ffir den Wasserhaushalt und die Trockenresistenz von Nadelbaum (English summary). In: H. Schmidt-Vogt (Editor), Proc. IUFRO Working Group on Characterization of Plant Material, Freiburg, Federal Republic of Germany, pp. 115-125. Lulandala, L.L.L., 1978. The establishment techniques of Leucaena leucocephala: effects of different treatments on the germination, survival and growth performance. M.Sc. Diss., University of Dar es Salaam, Tanzania. McKimm, R.J. and Flinn, D.W., 1979. Eucalypt species, site preparation and fertilizer requirements for afforestation fo the Toorongo Plateau in central Victoria. Aust. For., 42:117-124. Solberg, K.H. and Lysholm, G., 1979. EAC/NORAD lowland afforestation projecto1973-1975; summary report. Department of Silviculture, Agricultural University of Norway, As, 96 pp. Tanzania Forest Division, 1984. Trees for village forestry. Ministry of Lands, Natural Resources and Tourism. Dares Salaam, 125 pp.
103
Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands
E f f e c t s of S i t e P r e p a r a t i o n and F e r t i l i z e r A p p l i c a t i o n at P l a n t i n g on Eucalyptus tereticornis at M o r o g o r o , T a n z a n i a S.A.O. CHAMSHAMA and JOHN B. HALL*
Division of Forestry, University of Dares Salaam, Morogoro (Tanzania) *Present address: Department of Forestry and Wood Science, University College of North Wales, Bangor, Gwynedd LL57 2UW (Great Britain) (Accepted 28 July 1986)
ABSTRACT Chamshama, S.A.O. and Hall, J.B., 1987. Effects of site preparation and fertilizer application at planting on Eucalyptus tereticornis at Morogoro, Tanzania. For. Ecol. Manage., 18: 103-112. Uniform nursery stocks of Eucalyptus tereticornis were used to establish an experiment factorially combining site preparation (three levels - - bedding; disking; neither bedding nor disking), initial nitrogen applications (two levels - - 75 g ammonium sulphate per plant; 0 g ammonium sulphate per plant) and initial phosphorus applications (150 g triple super phosphate per plant; 0 g triple super phosphate per plant). Monitoring was carried out for 2 years by which time trees were up to 3.2 m tall and 5.0 cm in diameter at the root collar. Survival at 2 years was significantly higher among plants that had received nitrogen (65%) than those which had not (53%) and among plants on disked or bedded sites (62%) than those on unworked soil (53%). Monthly height increment was briefly, but significantly, increased in plants supplied with additional nitrogen and further enhanced if there was also additional phosphorus. Monthly diameter increment was, over most of the 1st year, significantly greater on sites prepared by bedding; significant increases also resulted, though for more restricted periods, from site preparation by disking and from provision of additional nitrogen. At the end of I year significantlyhigher concentrations of foliar potassium, suggesting enhanced drought hardiness, were detected for plants on bedded or disked ground. The concentration in these was 1%; on unworked ground the corresponding value was 0.8%. Combining bedding or disking with an initial application of nitrogen offset this effect, The short period over which growth benefits from the site preparation and nitrogen application treatments is noted but it is stressed that initial growth encouragement is desirable with Eucalyptus and that overall benefits, as in improved survival, may be long term. The value of phosphorus applications under the prevailing conditions is considered unproven.
INTRODUCTION In the 1950's forest p l a n t a t i o n s in T a n z a n i a a n d other E a s t A f r i c a n count r i e s w e r e m a i n l y e s t a b l i s h e d i n m o n t a n e a r e a s w h e r e soils a r e c o m p a r a t i v e l y
0378-1127/87/$03.50
© 1987 Elsevier Science Publishers B.V.
104 fertile and water stress problems relatively infrequent. This, added to the fact that there was clean weeding through the taungya system used in raising plantations, generally resulted in good survival and growth of seedlings. Montane forests, however, are no longer cleared for plantation forestry. Instead, plantations are being extended to much drier areas - - often with relatively infertile soils. Forestry's traditional preoccupation with wood production on a national basis has limited local effort towards identifying species of afforestation value for dry areas. Advantage was taken of experience elsewhere with Azadirachta indica A. Juss., Cassia siamea Lain., Eucalyptus camaldulensis Dehnh. and E. tereticornis Sm. once the urgency for forestry to combat increasing fuelwood deficits in the Tanzanian hinterland was appreciated. Until there is more familiarity with indigenous alternatives and additional exotic species, these four are likely to remain the nucleus of the country's dry-area afforestation options. The remarkable form and growth rate in Tanzania of the Eucalyptus designated 'Zanzibar C' and interpreted (FAO, 1981 ) as a hybrid between the two species mentioned above has stimulated particular interest in E. tereticornis. Although E. tereticornis is the least hardy (Tanzania Forest Division, 1984 ) of the four species named, excellent form and impressive growth account for its popularity wherever conditions are suitable. Conditions at Morogoro favour E. tereticornis and it was therefore considered appropriate for this study. Successful afforestation in these areas requires drought-hardened seedlings of species which can survive long periods of water shortage and requires an improved microsite environment created by appropriate regimes of site preparation and fertilization, combined effectively. This study examines the effect of different site preparation techniques and applications of nitrogen and phosphorus on 2 years survival and growth of E. tereticornis. MATERIALSAND METHODS Study area The study was conducted at the University ofDar es Salaam Forestry Experimental Area at Mafiga, Morogoro, Tanzania (6 ° 50' S, 37 ° 38'E; 500 m). Mean annual rainfall (1976-83) is 733 mm; mean annual temperature is 24.5°C. Soils are fine loamy sands. Further site characteristics are given by Lulandala (1978), Chamshama (1984) and Chamshama and Hall (1984). Information on seed source and nursery procedures adopted is reported by Chamshama and Hall (1984). Experimental design A three-factor fixed effects factorial model was adopted to study the effects of three site-preparation treatments (control, bed and disk), two levels of N
105 fertilizer (0 g and 75 g a m m o n i u m sulphate per plant) and two levels of P fertilizer (0 g and 150 g triple superphosphate per plant). The twelve treatments were each represented once in each of four replicate blocks.
Initiation and maintenance of experiment Before treatments were imposed, soil samples were taken from block centres for the depth range 0-30 cm. Site preparation was carried out in February 1981. The control t r e a t m e n t involved chopping of the vegetation: no further site preparation accompanied this. A single gang harrow pulled by a tractor was used to prepare the beds of the bed treatment, ridges 15-20 cm high being formed by making two passes of the harrow and rolling the soil towards the middle of the strip. The disk (complete cultivation) t r e a t m e n t consisted of ploughing, harrowing and disking to a depth of about 20 cm. Seedlings were planted manually in March 1981. Planting espacement was 2.5 × 2.5 m, and 49 seedling were planted in each replicate of each treatment. In the bed t r e a t m e n t seedlings were planted in the centre of the ridges. Fertilizers were applied 1 day after planting out as a 15-cm radius ring around each seedling treated. Complete manual weeding was carried out at intervals of about 3 months for 2 years.
Monitoring and sampling procedures At ages of 1, 3, 6, 12, 18 and 24 months, assessments of the inner 25 plants per replicate per t r e a t m e n t were made, for survival, height and root collar diameter at points marked 2 cm above the soil surface at the time of planting. Foliar samples were collected for nutrient analysis from a random sample of two plants per replicate per t r e a t m e n t at 12 months and 24 months after planting. Leaves were collected from the upper one-third of the crowns of sampled trees. Fully developed leaves in the outer part of a branch, taken at random, composed the sample. Soil samples from the 0-30 cm depth range were twice collected from the centre of each replicate of each t r e a t m e n t - - 12 months and 24 months after planting.
Laboratory procedures Foliar samples were carefully washed with distilled water to remove dust, then air dried, placed in paper bags and oven-dried at 70 ° C for 72 h. After oven drying, samples were ground in a Christy and Norris mill. Total N was determined by the macro-Kjeldahl procedure. For the determination of other nutrients, ground samples were ashed at 450 ° C in a muffle furnace for 3 h and the ash digested in 6 N hydrochloric acid. Aliquots of the solution were used to
106
determine P colorimetrically and K, Ca and Mg by using an atomic absorption spectrophotometer. Soil samples were oven dried at 70 °C for 72 h and sieved to pass through a 60-mesh sieve. The following determinations were made: exchangeable K, Ca and Mg; available P; and total N. Exchangeable cations were leached from the soil using neutral 1N ammonium acetate and individual cation concentrations were estimated by atomic absorption spectrophotometry. Phosphorus was extracted by the Bray and Kurtz method number 1 (Bray and Kurtz, 1945) and the concentration estimated colorimetrically by the blue molybdenum method. Nitrogen was estimated by the macro-Kjeldahl technique.
Statistical analyses All data were subjected to analyses of variance. Percentage figures were transformed (angular transformation) before analysis of variance was done. Differences associated with different levels of a factor were examined by use of orthogonal contrasts. RESULTS
Seedlings 30 cm tall were planted in the field. At the end of the 24-month observation period the trees monitored in this study ranged from 2.59 m to 3.24 m in height and from 3.85 cm to 5.02 cm in root collar diameter (Table 1). TABLE 1 Mean heights (m, upper figures), mean root collar diameter (cm, middle figures) and survival (%, lower figures) ofE. tereticornis after 24 months in the field at Morogoro, Tanzania Site preparation
Neither bedding nor disking Disking not bedding Bedding not disking
Initial fertilizer application (per plant) No fertilizer
Ammonium sulphate (75 g) only
Triple super phosphate (150 g) only
Ammonium sulphate (75 g) and triple super phosphate (150 g)
2.79 4.13 56 2.72 4.36 56 2.94 4.84 51
3.12 4.54 55 2.95 4.65 69 3.02 5.02 65
2.78 4.40 36 2.59 3.85 59 3.00 4.92 58
3.24 5.02 64 3.02 4.33 66 2.84 4.60 72
107 TABLE 2 Significant effects on E. tereticornis survival of initial applications of nitrogen fertilizer (75 g ammonium sulphate per plant) and bed and disked site preparation treatments at Morogoro, Tanzania Assessment age (months)
Factor significant
Contrasting factor levels and mean survival ( % )
12
nitrogen fertilization (P < 0.001 ) site preparation (P < 0.05 ) nitrogen fertilization (P < 0.001 ) nitrogen fertilization ( P < 0.001) site preparation ( P < 0.05 )
fertilization (68.8), no fertilization (58.2) bedding/disking (66.3), no bedding/disking ( 58.0 ) fertilization (66.3), no fertilization ( 54.2 ) fertilization {65.1 ) no fertilization (52.7) bedding/disking (62.0), no bedding/disking (52.8)
12 18 24 24
TABLE 3 Significant direct effects on E. tereticornis height (cm month-~) and diameter (mm month ~) increments of initial applications of nitrogen fertilizer (75 g ammonium sulphate per plant) and bed and disked site preparation treatments at Morogoro, Tanzania Assessment period ( months since planting)
Increment parameter
Factor significant
Contrasting factor levels and mean increments
2-3
height
2-3
diameter
2-3
diameter
4-6
diameter
4-6
diameter
7-12
diameter
nitrogen fertilization (P<0.001) nitrogen fertilization ( P < 0.001 ) site preparation (P < 0.01 ) nitrogen fertilization ( P < 0.001 ) site preparation (P<0.05) site preparation (P < 0.05 )
fertilization (8.4), no fertilization (15.0) fertilization (2.57), no fertilization (1.75) bed ( 2.45 ) ; disked ( 2.05 ), no bedding/disking (1.98) fertilization (1.51), no fertilization (1.03) bed (1.50), disking and no bedding/disking {1.15) bed (1.80), disking and no bedding/disking (1.40)
Survival percentage was found to reflect ( Table 2 ) the treatments applied but o n l y at t h e late a s s e s s m e n t s (12, 18 a n d 24 m o n t h s ) . T h e f a c t o r s i n v o l v e d w e r e N f e r t i l i z a t i o n a n d site p r e p a r a t i o n ; n o s u r v i v a l d i f f e r e n c e s w e r e a s s o c i a t e d with P fertilization. No interactions between factors influenced survival. Survival was highly significantly enhanced by N fertilization, the advantage subsequently persisting. Site preparation had a positive but comparatively weak
108 TABLE 4 Effects on height increment (cm m o n t h 1) of E. tereticornis in the 2nd and 3rd month in the field of initial applications of nitrogen fertilizer (75 g ammonium sulphate per plant) and phosphorus fertilizer (150 g triple super phosphate per plant) at Morogoro, Tanzania Phosphorus fertilizer
Nitrogen fertilizer
not applied applied
not applied
applied
8.75 13.97
8.03 16.09
Least significant difference (P~-0.05): 3.38. TABLE 5 Effects of foliar potassium concentration (%) of E. tereticornis after 12 months in the field of initial application of nitrogen fertilizer ( 75 g ammonium sulphate per plant) and bed and disked site preparation treatments at Morogoro, Tanzania Nitrogen fertilizer
Site preparation treatments
bedding disking neither bedding nor disking
applied
not applied
0.97 1.06 0.82
1.19 0.83 0.86
Least significant difference {P = 0.05 ) : 0.31. TABLE 6 Effects on foliar potassium concentration (%) of E. tereticornis after 12 months in the field of initial applications of nitrogen fertilizer (75 g ammonium sulphate per plant) and phosphorus fertilizer {150 g triple super phosphate per plant) at Morogoro, Tanzania Phosphorus fertilizer
Nitrogen fertilizer
applied not applied
applied
not applied
1.04 0.86
0.90 1.00
Least significant difference (P=0.05) : 0.17. effect, s i g n i f i c a n t o n l y f o r t h e r a i n y s e a s o n a s s e s s m e n t s (12 a n d 24 m o n t h s ) . N o s i g n i f i c a n t s u r v i v a l d i f f e r e n c e s w e r e a s s o c i a t e d w i t h t h e d i f f e r e n t site p r e p aration methods used. Height increments were found to reflect N and P fertilization only during
109 TABLE 7 Nutrient concentrations in the soil for depth range 0-30 cm at Mafiga, Morogoro, Tanzania prior and subsequent to site preparation by bed and disking treatments Nutrient
Total nitrogen (%) Available phosphorus (ppm) Exchangeable potassium (meq per 100 g) Exchangeable calcium (meq per 100 g) Exchangeable magnesium (meq per 100 g)
Concentration after 24 months Prior to treatment
Following bedding
Following disking
0.04
0.04
0.05
8.80
8.91
8.77
0.74
0.61
0.72
8.46
8.45
8.30
1.34
1.04
0.95
the second and third months in the field (the height of the 1981 rainy season). Nitrogen fertilization accelerated height growth (Table 3) both as a direct effect and through an interaction with P fertilization (Table 4). Phosphorus fertilization had no direct effect on height increment. Neither direct nor interaction effects of site preparation on height increment were revealed. Diameter increments were significantly influenced (Table 3 ) during the last three of the four assessment intervals consituting the 1st year in the field, by treatments applied. Nitrogen fertilization accelerated diameter growth from the 2nd to the 6th month in the field during which time soil moisture tension remained moderate ( < - 4 bar). Site preparation promoted diameter growth from the 2nd month to the 12th; initially, bed treatments induced significantly faster growth than disking which, in turn, induced significantly faster growth than control conditions. From months 4-12, however, the advantage of disked over control treatments disappeared while the bed treatment remained significantly superior to both. At no stage was there any significant effect on diameter increment of P fertilization or interactions between factors. After 12 months, no significant effects on diameter increments were found with any treatment. There was evidence only for the 12-month samples that treatments applied influenced foliar nutrient concentrations and then only in the case of K. All factors exerted influence on foliar K concentration through interaction effects but only with site preparation was there also a direct effect. Foliar K concentration for trees planted where there had been no bedding or disking was significantly ( P < 0.05 ) lower ( 0.84% ) than for trees planted on ground prepared by either bedding or disking (combined mean, 1.01% ). The significant inter-
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action effects were of site preparation with N fertilization (Table 5 ) and of N fertilization with P fertilization (Table 6). Soil nutrient levels ( Table 7 ) did not change significantly during the period of study. DISCUSSION
If both are beneficial, it is logical to combine site preparation operations with fertilizer applications to improve seedling survival and growth prospects during the sensitive period after planting. Experimental studies mostly look at these factors separately, however. No studies in the drier parts of East Africa have considered interactions of fertilizer applications and site preparation as they affect Eucalyptus performance, although Solberg and Lysholm (1979) report use of this approach with Pinus caribaea Morelet. Determination to extend planting into the drier areas of Tanzania in the coming years to counter trends of diminishing fuel supply warrants attention to this topic since seed availability, silvicultural familiarity, rapid growth potential and suitability for fuel indicate that Eucalyptus spp. will be used very widely. Indications ( Chingaipe, 1985) that Eucalyptus can approach or reach its potential only when appropriate management is applied from the earliest stage underline the importance of sound initial establishment-promoting procedures. This study has demonstrated that under Morogoro conditions effects of both fertilization and site preparation are reflected in the early growth ofE. tereticornis and that interactions involving fertilizer applications and site preparation arise. A brief (1 or 2 months) lag ensued between planting and response to experimental treatments, presumably because initially plants depended on the soil balls inherited from the tubes used for nursery propagation. Thereafter, positive effects from site preparation and fertilizer applications were expressed as enhanced increment until the end of the first 12 months. The most persistent benefit was from site preparation but, of the two preparatory measures taken, only the bed treatment led to accelerated diameter growth after the 3rd month. The site conditions in the experimental area are such that the benefits of bedding are probably from concentration in the ridges of humus, litter and topsoil leading to more available nutrients and allowing more moisture retention and a longer period of moisture availability than in unprepared soil. The earlier (after only 6 months) cessation of benefits from N fertilization suggests that by the time the rainy season ends any available N additional to that normally present at the site has disappeared - - perhaps through leaching in the rainy season or mineralisation as the soil dries out. The shorter annual period of vigorous height growth typical of woody plants in strongly seasonal climates ( Hopkins, 1970 ) explains the short-lived expression of the height increment enhancement associated with the initial application of N. The apparent loss of extra N before the next growing season would
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account for the absence of a similar response in 1982. The involvement of P in a beneficial interaction with N is a situation reported elsewhere ( Cromer, 1971 ). Here, the absence of direct effects, the restriction of significance to a single set of height increment data and the marginal level of significance all suggest a chance result; lack of response of Eucalyptus to P application has been noted often and McKimm and Flinn {1979) surmise that members of the genus, having evolved on P-poor soils, require less of the element than do most other plants. For the other parameters examined, the significant responses noted refer to cumulative effects; though detectable in data collected from 12-24 months after planting, the benefits may have been conferred within the 1st year and persisted thereafter. Thus, if N fertilization ensured improved establishment and survival over the critical early period, by the time plants had been in the field for a year they would face less risk of mortality and the effect of the treatment would remain. Explanation of the effect on survival of site preparation is less straightforward. In contrast with effects on diameter growth, advantages of both preparatory treatments over unprepared soil persisted, perhaps because thorough destruction of pre-existing vegetation matters more for survival. The temporary interruption of this advantage revealed by the 1981/82 dry season assessment may indicate resumption of soil water recharge too late to benefit all individuals favoured earlier by site preparation activities. Enhancement of K uptake indicated by higher foliar concentrations 12 months after planting requires further investigation since no earlier checks were made. It is unclear why such a response should directly be promoted by both types of soil preparation or through interactions of site preparation effects with N fertilization. The effect, however, is considered beneficial - - higher K status signifies increased drought hardiness. The findings of this study should influence establishment practice for E. tereticornis in sandy soils in areas enjoying 600-800 mm mean annual rainfall. The brevity of periods when significantly faster growth occurred does not invalidate routine use of the treatments responsible; the benefits persist and their importance is real because Eucalyptus responds most positively to the earliest provision of favourable growing conditions. The key operation is site preparation by bedding, with its long period of growth promotion and its apparent increasing of drought-hardening. The better growth arising when there had been initial N fertilization might not be accompanied by a similar advantage if Eucalyptus reacts to this in the same way as softwood species ( Larsen, 1980 ) ; in combination with site preparation treatments this might counter any tendency towards enhanced drought hardiness. A choice may be necessary between emphasis on increased drought hardiness (avoid N fertilization on sites deemed risky) and accelerated growth (N fertilization appropriate on sites with predictable rainfall patterns). Routine P fertilization does not appear justified in view of its inconsistent
112 ( a n d n e v e r m a r k e d ) a s s o c i a t i o n w i t h s i g n i f i c a n t l y i n c r e a s e d g r o w t h a n d its a p p a r e n t lack of effect on survival. ACKNOWLEDGEMENTS T h e w o r k described was facilitated by f u n d i n g f r o m the N o r w e g i a n A g e n c y for I n t e r n a t i o n a l D e v e l o p m e n t as p a r t o f its S t a f f D e v e l o p m e n t P r o g r a m m e for t h e Division of F o r e s t r y , U n i v e r s i t y o f D a r es S a l a a m . We t h a n k t h e H e a d s a n d t h e t e c h n i c a l a n d n u r s e r y s t a f f of t h e U n i v e r s i t y ' s Division of F o r e s t r y a n d Soil Science D e p a r t m e n t for a s s i s t a n c e w i t h a n a l y s e s a n d e x e c u t i o n of r o u t i n e field m a i n t e n a n c e activities.
REFERENCES Bray, R.H. and Kurtz, L.T., 1945. Determination of total, organic and available forms of phosphorus in soils. Soil. Sci., 59: 39-45. Chamshama, S.A.O., 1984. Establishment techniques for Eucalyptus species: effects of nursery treatments, site preparation and fertilization on survival and growth. Ph.D. Thesis, University of Dares Salaam, Tanzania. Chamshama, S.A.O. and Hall, J.B., 1984. Height graded Eucalyptus tereticornis seedlings: one year field performance. For. Ecol. Manage., 7: 225-232. Chingaipe, T.M., 1985. Early growth of Eucalyptus camaldulensis under agroforestry conditions at Mafiga, Morogoro, Tanzania. For. Ecol. Manage., 11: 241-244. Cromer, R.N., 1971. Fertilizer trials in young plantations of eucalypts. Aust. For. Res., 5: 1-10. FAO, 1981. Eucalypts for Planting. FAO For. Ser. 11, Food and Agriculture Organization, Rome, 677 pp. Hopkins, B., 1970. Vegetation of the Olokemeji Forest Reserve, Nigeria. VII. The plants on the savanna site with special reference to their seasonal growth. J. Ecol., 58: 795-825. Larsen, J.B., 1980. Die Bedeutung der Nahrstoffversorgung ffir den Wasserhaushalt und die Trockenresistenz von Nadelbaum (English summary). In: H. Schmidt-Vogt (Editor), Proc. IUFRO Working Group on Characterization of Plant Material, Freiburg, Federal Republic of Germany, pp. 115-125. Lulandala, L.L.L., 1978. The establishment techniques of Leucaena leucocephala: effects of different treatments on the germination, survival and growth performance. M.Sc. Diss., University of Dar es Salaam, Tanzania. McKimm, R.J. and Flinn, D.W., 1979. Eucalypt species, site preparation and fertilizer requirements for afforestation fo the Toorongo Plateau in central Victoria. Aust. For., 42:117-124. Solberg, K.H. and Lysholm, G., 1979. EAC/NORAD lowland afforestation projecto1973-1975; summary report. Department of Silviculture, Agricultural University of Norway, As, 96 pp. Tanzania Forest Division, 1984. Trees for village forestry. Ministry of Lands, Natural Resources and Tourism. Dares Salaam, 125 pp.