EFFECT OF DIFFERENT SALINITY LEVELS ON SEED GERMINATION OF SALT TOLERANT TREE SPECIES

K. K. I. U. Aruna Kumara U. Wickramasinghe R. Senarathne
Department of Crop Science Faculty of Agriculture University of Ruhuna

An experiment was conducted, during March-July 2000,at the Faulty of Agriculture, University of Ruhuna, Mapalana, Kamburupitiya, to study of the effect of levels of salinity on seed germination of three salt tolerant species, namely Acacia leucoploea (Katu Andara), Parkinsonia aculeate (Parkinsonia) and Cassia auriculate (Ranavara)

The experimental design used, was Randomized Complete Block Design with 5 treatment and 4 replications. Here, sea water (40 ds/m) was diluted to give varying salinity levels (i.e. 2, 4, 8, and 12 ds/m) and normal water (0.13 ds/m) was used as the control. Saline solutions were applied to seeds and the rate and percentage germination was observed.

The results obtained from the experiment showed that, low salinity levels (4 ds/m) increased seed germination of all 3 species. But with increasing salinity beyond 8 ds/m a decreasing in germination was observed. When the salinity level was 8 ds/m, the percentage of germination in Katu Andara, Parkinsonia and Ranavara about 40, 40 and 13 respectively.

The percentage of germination in Ranavara was 0 at the salinity level of 12 ds/m. But in Katu Andara and Parkinsonia, 23% and 15% germination was observed at 12 ds/m. Thus, these species can be ranked in oder of tolerance to salinity as follows:
Katu Andara > Parkinsonia > Ranavara

NITROGEN STATUS AND ITS SUPPLYING CAPACITY OF TROPICAL SOILS.

K. A. Nandasena
Department of soil Science Faculty of Agriculture
University of Peradeniya

Total Nitrogen content in tropical soils ierally low compared to the most temperate soils. About 98% total nitrogen is associated with soil organic matter which in turn subjects to mineralization and hence releases mineral nitrogen to the soil. Thereby most tropical soils nitrogen supplying capacity or nitrogen mineralization potential is relatively low and declines rapidly during cropping season unless nitrogen sources are incorporated frequently. This investigation conducted to find out the nitrogen status, distribution of different nitrogen fractions and the mineralization potential of some selected agriculturally important soils of Sri Lanka.

Sixteen soils collected from various locations representing different soil types were analysed for total nitrogen. Eight soils from sixteen soils were fractionated and analysed for different nitrogen forms viz; available N, ammonia-N, amino sugar-N, amino acid-N, acid hydrolyzable unknown N and acid insoluble-N after acid hydrolysis. In a laboratory incubation experiment, those eight soils were subjected to follow the nitrogen mineralization potential and to determine the mineralization rates according to the method described by Stanford and Smith (1972). The nitrogen mineralization data during 315 days of inclubation were used in Stanford and Smith's first order decay model to calculate nitrogen mineralization rate(k) and nitrogen mineralization potential (No).

Total nitrogen contents in the studied soils varied from 89.36 (Aralaganwila) to 365 mg/100 g soil (NuwaraEliya). Soil organic matter contents also gave similar variation and showed close relationship with total soil nitrogen. The distribution of different forms of soil nitrogen also varied among the soils studied. A major part of organic nitrogen in Sri Lankan soils was found to be associated with amino acid-N fraction followed by the ammonia-N fraction. This was consistent with the other studies conducted in elsewhere (Stevenson, 1957; 1982)Nitrogen mineralization rate was ranged from 0.0069 to 0.026 N mg/100 soil per day. Highest mineralization rate was given by two paddy soils (Kiribathkumbura and Pilimathalawa).

Nitrogen mineralizations potential or nitrogen supplying power also varied from 5.33 to 38.52 N mg/100 g soil. High mineralization potential was also recorded in paddy soils. This may be attributed to the high organic matter contents in those soils. Further these different nitrogen supplying powers of soils reflect their inherit characteristics or potential in supplying available nitrogen for plant usage. One should give serious consideration to those parameters of soil nitrogen when nitrogen fertilizer recommendation practices are conducted for crops to attain optimum yield.

RELEASE OF MINERALIZED NITROGEN FROM SOILS AFTER INCORPORATION OF DIFFERENT ORGANIC MANURES.

K. A. Nandasena and R.P.U.G. Balasooriya
Department of soil Science Faculty of Agriculture
University of Peradeniya



Use of organic manures as a nutrient Source for crops is common practice in agriculture. Added advantages of using organic manures against synthetic fertilisers are the positive influence on physico-chemical and biological characteristics of soils. Release of mineral nitrogen from organic manures could be used as an index to check the quality of organic manures in relation to nutrient supply to the crops. Therefore, the objective of the present laboratory leaching study was to monitor the nitrogen release from soils after addition of selected organic manures.

Two surface soils, Reddish Brown Earths and Non Calcic Brown (0-30cm) collected from Mahallluppallama and Aralaganwila areas respectively, were used in this study. Soils were mixed with three organic manures; Poultry manure (PM), Glyricidia leaves (GM) arid Rice straw (RS) at the rate of 20 and 40 tons/ha. There were four treatments; 1). Soil only - control, 2). Soi1+PM. 3). Soil +GM and 4). Soil + RS. Each soil-organic manure mixture was placed in leaching columns and incubated in dark at room temperature. Mineralised nitrogen (NH+4 - N and N03 -N) was extracted with 0.01M CaCIZ solution at 7, 14, 21, 35 and 49 days after incubation using the method described by Stanford and Smith (1972). The NH+4 -N and NO3 - N contents were determined by using standard Kjeldhal method. The physico-chemical and nutritive characteristics of soils and organic manures were determined bv using standard laboratory methods. Results of the study revealed that the application of organic manures has pronounced effect on the release of nitrogen. In both soils, 40 tons/ha level showed higher release of nitrogen compared to 20 tons/ha level. Out of three organic manures, PM treated soils showed a higher release of nitrogen followed by GM treated soils. The RS treatment showed a very low release of nitrogen which is caused by the immobiolisation in two soils during the incubation. It was very clear that the release and immobilisation of nitrogen are controlled by theC/N ratios of organic manure. Up to 7`h day the nitrogen release from PM and GM treated soils was high against the control as well as RS treated soils. After 7`h to 21`h day, the mineralisation and release of nitrogen was decreased and subsequently it was increased up to 35`h day and then again decreased at the end of incubation with few exceptions. In general, the proportion of NH+4 -N to N03 - N was high at the early stage of the incubation compared to the latter stage of incubation. This may be attributed to the transformation of more NH+4 - N to N03 -N by the nitrification process operating at the higher rate at the latter stage of incubation. The release of NH -N and NO -N from organic manures was significantly higher than the control at certain sampling times. However, according to this study, the use of organic manures such as PM and GM with C/N ratios will enhance the mineral nitrogen content in soils during the first week of incorporation

EFFECT OF LIMONOID AND NITROGEN COMPOSITION IN SHOOTS OF Swetenia macrophilla (KING).

Rizana M Mahroof1 Jayanthi P Edirisinghe1 Caroline Hauxwall2
1Department of Zoology, Faculty of Science
University of Peradeniya
2Institute of Ecology and Resource Management
University of Edinburgh

The main factor limiting cultivation of mahogany, Swletenia macrophylla King (Meliaceae), in plantations is damage by shoot borers (Hypsloyla spp.). Shade has been repeatedly cited as reducing shoot borer attack but the responsible mechanisms have not been determined by experimentation. Shade may alter either secondary compounds such as limonoids or nitrogen concentrations or both in the plants making them unsuitable for insect survival and development. Previous studies have not examined whether shade influences limonoid and nitrogen content of S.marcrophylla and thereby alter shoot-borer attack. Therefore, these studies were designed to identify the variation in incidence of shoot borer attack under three levels of shade treatments in the field conditions and the variation in plant chemistry of S.marcrophylla shoots grown under three different artificial shade treatments. The hypotheses tested were under high light availability (i) incidence of shoot borer attack increases (ii) the concentration of limonoids present in the shoots of S. macrophylla decreases ind(iii) total nitrogen content of shoots increases.

This study was done from 1997-99 in Sri Lanka and UK. Attack by the shoot borer was assessed 54 weeks after planting. The Limonoid content was investigated by Thin Layer Chromatography (TLC) and the total nitrogen by Kjeldhl method using freeze-dried ppowdered shoots. The incidence of shoot borer attack was significantly higher under low shaade (d.f.=2, F=8.6, p=0.0003). The intensity of the green-blue fluerescence under UV seen in the TLC plates was greater using the extracts from the high shade treatment compared to that from the low shade treatment. The total nitgrogent content was satistically lower in the high shade (1.114± 0.22%, n=33) compared to that in full light (1.36± 0.22%; n=31). These results suggest that light environment may have a significant effect on the concentrations of limonoids and nitrogen in S.macrophylla which in turn influences the shoot borer attack.

The study forms part of a larger project on 'Silvicultural prescription for mahogany plantation establishment; Research grant funded by DFID, UK is greatfully acknowledged

STUDIES ON DORMANCY AND GERMINATION DYNAMICS OF MACRANGA PEETATA (KANDA) AN EARLY SUCCESSIONAL SPECIES.

K. K. I. U. Aruna Kumara U. Wickramasinghe G. A. Dayathilaka R. Senarathne
Department of crop science, facuiry of Agriculture, university of Ruhuna

Macaranga peltata is one of the most widely occurring early successional woody species, specially in low country wet zone. Although Macaranga spreads profusely by seeds, the seed biology and germination behavior has not been studied. According to the preliminary studies, it was revealed that, the germinability of freshly isolated seeds is very low. Therefore this work was undertaken to understand the germination behavior and measures to enhance seed germination of Macaranga. The study was conducted during May-July, 2000, at the faculty of Agriculture, University of Ruhuna, Mapalana, kamburupitiya, Sri Lanka.

Three treatments used, i.e. mechanical scarification using sand papers (T,), Chemical scarification using HZSO4 acid (Tz) and hormone treatment using GA (T3), with the control. Fully ripened seeds were harvested and thoroughly washed to remove the peel and air-dried for one day. Dried seeds were treated as indicated above and placed in petri dishes containing sand media and allowed to germinate. Three replications were used for each treatment and percentage of germination was recorded at 7,14,21 and 28 days after planting.


Germination of Macaranga seeds started after 14-21 days in control by after seven days in treated seeds. Mechanical and chemical scarifications were not effecting in increasing the percentage of germination significantly. But the gibberelic acid treatment has made a tremendous important in the percentage of germination and at the same time resulted in significant reduction it time taken for germination. Although scarification treatments may have improved permeability of seed coat, it has not contributed to the germinability of seeds, the significant impact made by GA treatment both in increasing and accelerating the germination probably reveals that there exists a dormancy in Macaranga seeds which is of physiological or metabolic in nature GA treatment of more effectively at higher concentration: (20mm) was capable of breaking the dormancy and thus enhanced germination.

Keywords: Macaranga peltata, Seed germination, dormancy, gibberalic acid_

SEEDLING SURVIVAL AND GROWTH OF NINE LATE SUCCESSIONAL SPECIES ACROSS TOPOGRAPHIC GRADIENT IN SRNHARAJA RAIN FOREST

1E. P. S. K. Ediriweera 1B. M. P. Singhekumara 2P. M. S. Ashton
1Department of Forestry and Environmental Science, Univer sity of Sri Jayewardenepura
2School of Forestry and Environmental Studies, Yale University, New Heven, U.S.A.

Growth performance of seedlings belong to nine late-successesional canopy tree species was studied at three different topographic positions (ridgetop, midslope and valley) in the Sinharaju rain forest, southwest Sri Lanka. Seedlings were planted in plots located in valleys, midslops and ridgetops. In each site four canopy openings and four adjacent understoreys were selected to plant seedlings of nine late-successional canopy tree species. Seedling growth and mortality were monitored for three years.

Results demonstrated that a clear difference in survival and growth among species. These differences appeared to be related to the availability of soil moisture and groundstorey radiation regimes of the forest. Shorea disticha exhibits high growth rate than others in each topographic position in each site. Seedlings of Mesua ferrea and Shorea megistophylla exhibit a higher survival than other species in canopy openings and understorey conditions of all topographic positions. Growth performance and survival of their species will be monitored for several years to study the nich specialization of the late-successional canopy tree seedlings

BIOMASS AND NUTRIENT ACCUMULATION OF AN EARLY SUCCESSIONAL SHRUB SPECIES (ZIZYPHUS OENOPLIA) IN AN UPROOTED RUBBER FIELD AT KAMBURUPITIYA

K. K. I. U. Aruna Kumara U. Wickramasinghe R. Senarathne
Department of Crop Science, Faculty of Agriculture, University of Ruhuna

Restoration of degraded ecosystems has become a matter of great concern. Early successional species play a key roll in the process of restoration. Therefore here a study was undertaken to assess the accumulation and partitioning of biomass and nutrient in widely occurring early successional shrub species, namely 7.izyphus oenoplia (Eraminiya) of varying ages (i.e. 4, 6 and 8 years). The experiment was conducted at the faculty of Agriculture, University of Ruhuna, Mapalana, Kamburupitiya, during March-August, 2000. Here, four plots were selected for each age class and four plants were sampled for each plot and their distribution of dry matter and major nitrient (NPK) in stem, branches and leaves were measured in each plant.

Findings clearly indicate that majority of biomass was concentrated in plant stem and as the age progressed, this proportion is increased. These results further indicate that the biomass allocation to the leaves was high in young ages and it is decreasing as the age progressed. Total biomass of plant after 4, 6 and 8 years was 902, 2602 and 4552 g respectively.

Results also show that major nutrient content in leaves, branches and stem were high in early stages of the growth and decreasing as the age progressed. Percentage of N. P and K in leaves at 4 years were 2.91, 0.116 and 1.54 respectively. But after 8 years N. P and K content were 2.36, 0.093 nd 1.275% respectively, show a decreasing rend of concentration of major nutrient in leaf tissues. Stem and branches show the same pattern of nutrient partitioning as the plant getting matured.

PRELIMINARY SURVEY OF SERPENTINE VEGETATION IN UDA WALAWE AREAS

N Wickramaratne
Department of Geography, University of Peradeniya

Serpentine, bearing the general formula: Mg3Si,OS(OH)a denotes a group of hydrous, magnesium silicate minerals. Sri Lanka too, serpentine bodies occur roughly on the boundary of Vijayan and Highland series of rocks. The three principal serpentine areas of Sri Lanka are 'Ginigal-pelessa' and 'Indikola-pelessa' both close to Uda Walawe and, 'Ussangoda' near Nonagama Junction.

Within broad climatic zones, soils developed on serpentine mineral substrates harbor unique vegetation communities. Such communities are referred to as lithobiomes and have attracted scientific attention. Other examples of lithobiomes are vegetation on limestone and saline soils etc., which are interspersed within zonal soils.

Ginigal-pelessa and Indikola-pelessa serpentine bodies are located about three kilometers apart. The area receives a rainfall of about 1325mm/yr and the average number of rainy days per year is 94. The maximum amount of rain comes between October and December.

The objective of the present study was to initiate a survey of vegetation in these two unique areas. The study was initially begun in September 1998 in Ginigal-pelessa and was extended to Indikola-pelessa in 1999. It included reconnaissance of the two areas followed by a survey of plant species and soil. Woody plant species were studied in 10 x lOm quadrats whereas, grasses and herbaceous plants were examined in 1 x lm quadrats. Density of the grass vegetation and the abundance of woody plants along with girth were recorded. Slope of the areas was measured with an Abney level. Also examined in each area was a shallow soil pit and soil depth was measured in selected points, by means of an auger. Soil color was determined with the aid of a color chart, yet no soil chemical analyses were done.

In Ginigal-pelessa the maximum slope is 15% and it is 12% in Indikola-pelessa. The substrate in both places is an undifferentiated soil developed from serpentine minerals. It is shallow (<45cm in Ginigal-pelessa and <42cm in Indikola-pelessa) and overlies partly weathered serpentinite rocks. The color varies from 7.5 3/2 YR-wet. It is friable (dry) and very friable (wet). It is a silty loam, which is slightly sticky, and slightly plastic when wet. Reddish Brown Earth (RBE) Surrounds the two areas, where the terrain is slightly undulating. The aggregate extent of the two areas is more than four kmZ. Yet, only a few hectares of the associated vegetation remain fairly inact in Ginigal-pelessa whereas, almost the entire serpentine vegetation has been drastically changed in Indikola-pelessa.

The vegetation in both places has a savanna-like physiognomy though the woody plants are somewhat stunted. Dominant non-woody species is the tussock agrass, Cytnbopogon flezuosus Wats. This grass (max. Height 1.2m) along with other herbaceous and low woody plants provide a dense cover. The woody species are scattered apart.


In Ginigal-Pelessa 15 plant species belonging to 12 families were identified in the sampling quadrats.Based onlife form their distribution is as follow:herbs /grasses 03,creepers 02,low shrub spp. 02 shrub spp.05 and tree spp. 03.Among all woody specie Morinda tinctoria Roxb, is the most abundant.Spacial attributes are; mean distance 1.8m max. distance 25.6 m and min.distance 3.2m. Density of trees is 18 /1000m;, Max. tree height is 4m.

In Indikola-pelessa, a place of archaeological importance, 23 species belonging to 16 families were found. Their life form distribution is as follows: herbs/grasses 01, creepers 04, low shrub spp. 03, shrub spp. 03 and tree spp. 12. The dominance of Morinda tinctoria is not seen in this locality. Spartial atrtributes are; mean distance 4.465m. max distance 9.30m and min. Distance 1.9m. Dinsity of trees is 39/1000m2. Max. tree height is 3.5m whereas most of the tree species are in shrub form.

Absence of succulent xerophytes in both areas is striking. This suggests that microhabitat aridity is not a factor. Yet, the stunted nature of the plants may be due to other edaphic factors (e.g. shallow soil profile, mineralogical conditions). In both places periodic burning as in patanas, is an arresting factor.

In relatively undisturbed sites, near-normal growth of such wood species as Azadirachta indica A Juss. (neem), Teminalia catappa L. (Kottamba), Anatardium occidentale L. (cashew) and leucaena leucocephala Lam, (ipil-ipil) indicates that deep-rooted perennials can do well in these serpentine areas. Therefore, the area seems sustable for conservation forestry and wood-fuel lots.

THE SERPENTINE VEGETATION OF USSANGODA (HAMBANTOTA DISTRICT) AND NICKEL ACCUMULATING PLANT SPECIES

A S Seneviratne', H G Nandadasa2,W.S.Fernando3, H H V M Sanjeevani2 and R L H R Rajapakse2 '
1Department of Botany, University of Colombo
2 Department of Botany, University of Sri Jayewardenepura
3Department of Chemistry . University of Sri Jayewardenepura

The vegetation of serpentine soils has fascinated plant taxonomists, physiologists and ecologists. ~ Many serpentine plant species are used as indicator plants in geo-botanical exploration of mineral deposits and phyto-remediation of polluted soils. Some of the world's serpentine plants have the remarkable ability to selectively accumulate Ni from the soil.

Serpentine body at Ussangoda is overlaid with an ultrmattc soil, which is characteristically rich in Ni, Cr, Fe and Mg. The plain is called 'Rathupas thalawa' - Red soil plain - due to the deep red color of the soil. It is host to a unique type of vegetation tolerant of toxic edaphic condition. As is characteristic of serpentine floras in other parts of the world the vegetation is sparse and the species diversity is low. The plants are stunted prostate in habit and show stress features. The vegetation contrasts sharply with the adjacent non-serpentine vegetation of thorny scrubland and is comprised of plant associations dominated by Hyabanthus enneaspertnus, Evolvulu.s alsinoides, Fimbristylis falcata, Eutp/torbia indica, Crotolaria latebrosa and Blunrea obliyua. Among the other plants which are confined to specific areas on the plain and are of limited distribution are Phyllanthus simplex, Mollugo nudicattlis, Cassia mimosoides, Chlorophyton taxum, Fimbrisrylis acuminata, Polygala javana, Ischaenutm tintorense and Striga etrphrasiodes.

All the plants listed above are serpentine facultative. Of special significance is the occurrence of two types of Evolvulus alsinoides wither with blue flowers or with whiteflowers. Hybanthus enneaspermus is also found in two types either with pink flowers or with white flowers. The two flower types of Evolvuhus show distinct llavonoid profiles on paper chromatograms. The existence of 'flavonoid races' has been reported from other serpentine soils in the world.

The Ni content of the species analysed ranges from 173-2173 ppm on a dry weight basis and is as follows. Hybanthus enneaspermus 2174 ppm, Striga euphrasioide.s 1400 ppm, Cassia ntimosoides 1140 ppm, Bluntea obliqua 1054 ppm, Evolvulus alsinoides 1023 ppm, and Crotolaria latebrosa 604 ppm. This signifies that the mechanism of Ni tolerance is either detoxification and or extrusion rather than exclusion.

While the normal Ni content in plants is reported to be 2-15 ppm, all the serpentine species which we have analyzed were found to be accumulators (>100ppm.). Six of these were hyperaccumulators (>100ppm.). The significance of the above findings and the urgent necessity to conserve this unique vegetation and its habitat will be discussed.