Biomass production from naturally growing Melastoma (Melastoma affine, D. Don)

Bui Phan Thu Hang and Vo Lam

Angiang University, Faculty of Agriculture and Natural Resources, Vietnam
bpthang@agu.edu.vn

Abstract

A study was conducted at Hoaan Farming System Research Station of Cantho University, Haugiang province, Vietnam from May to November 2004 to estimate the biomass production of naturally growing Melastoma affine, D. Don in the acid sulphate soil area. Five Melastoma shrubs of 4 different height classes (<1.0 m; 1.0-1.9 m; 2.0-2.9 m and >2.9 m) were cut at 15-20 cm above ground. The edible foliage (leaves+petioles+40cm of stem) and woody stems were harvested and weighed to measure the total biomass yields from shrubs of different heights and proportion of edible foliage. Number of shoots and sub-shoots, average height of the shoots and sub-shoots were counted and measured once per month each individual plant to measure the ability of re-growth.

No Melastoma shrub higher than 2.9 m was found in the fields. The highest percentage of edible DM yield was from Melastoma below 2.0 m. Shrubs higher than 2.0 m were more suitable for fuel wood. After cutting, the number of shoots and sub-shoots was higher than the number of stumps and grew well. Twenty sub-plots (5m*5m) were also randomly selected and marked within 4 main plots (20m*20m) (5 sub-plots per main plot) for estimating biomass production per hectare in an area dominated by Melastoma. The total fresh biomass yield per ha was about 37.2 tons. The biomass of edible foliage was 1.5 times higher than the biomass of woody stems. The results showed that the height of naturally growing Melastoma strongly influenced the yield of edible foliage and woody stems.

Key words: biomass production, edible foliage, Melastoma affine, shoots, sub-shoots, woody stem

Introduction

The Mekong delta is one of the most fertile areas in Vietnam. Twenty one percent of the total of four million hectares of land consists of saline water soil, 28% is acid sulphate soil, and 17% both saline and acid sulphate soils (Anonymous 1995). Acid sulphate soils (ASS) affect agricultural productivity and the possibility to grow different crops in areas with this soil. The water in the canals contains high amounts of aluminum (16 meq/100 g) and has a low pH of 3.5 (SIDA-SAREC 1993). In the ASS lowland, water plants are present almost all year around. Many plants such asAlternathera repens, Amaranthus spinosus, Centella asistica, Manihot esculenta, Ipomeae batatas, Basella rubra and Sesuvium portulacastrum die in the flooding periods because they can not stand waterlogging (Dung 1996).

Melastoma affine is an evergreen, medium sized shrub with pink flowers which are present throughout the year and is very abundant in the fields and homestead areas. Melastoma affine has received little attention in the tropics and is not considered to be of any great value even though goats seem to like this plant.

The aim of this study was to estimate the biomass production of naturally growing Melastoma affine, D. Don in an acid sulphate soil area.

Materials and methods

Location and climate of study area

The study was carried out at Hoaan Farming System Research Station of Cantho University (9^o50’N, 105^o25’E), Haugiang province, Vietnam. The area is characterised by acid sulphate soil and is a lowland area often water logged. Soil pH is 4.5, annual rainfall varies from 1800 to 2000 mm and the mean temperature is 27.7^oC. Floodwater yearly dominates the area from September to October each year. The weather conditions during the study are shown in Figure 1. At the beginning of the study, the average temperature and humidity were 27.5^oC and 84.8% and at the end of the experiment 28.2^oC and 78.5%, respectively.

Figure 1. Monthly weather conditions in Hoaan village

Experimental design

The biomass production was studied by measuring total biomass from a number of existing shrubs, by following up re-growth after harvesting and by estimating the number of plants per unit area.

To estimate biomass from individual shrubs, 20 shrubs were selected in an area dominated by Melastoma, 5 in each of 4 height classes, <1.0 m; 1.0-1.9 m; 2.0-2.9 m; >2.9 m. The selected shrubs were cut at 15-20 cm above the ground and the foliage (leaves+petioles+40cm of stem) was harvested and weighed. The remaining stems were also weighed to get total fresh biomass above ground. Samples were taken from each plant, edible foliage (leaves+petioles and stems separately) and bigger stems for DM and ash analysis.

The total biomass production from shrubs of different heights is presented as fresh and as DM, and the edible foliage in percent of total DM.

The harvest of the shrubs was done in May, at the start of the rainy season. After the harvest the re-growth of each individual plant was followed up once per month, from June to November. Number of shoots were counted and measured and the average height of the shoots was calculated and presented with maximum and minimum heights.

To estimate biomass production per ha an area dominated by Melastoma was selected. Four main plots (20m*20m) were randomly marked. Five sub-plots (5m*5m) were randomly selected and marked within the main plot. Thus, there were twenty selected sub-plots. Within each sub-plot the number of Melastoma shrubs was measured and counted.

Chemical analysis

The DM and ash were determined according to AOAC (1990). Total DM was determined in a two-step process. First, the sample was partially dried by oven drying at 55oC and secondly, laboratory DM was determined by oven drying at 105oC. Total DM was then calculated by multiplying partial DM with laboratory DM.

A dried, ground sample was ignited in a furnace at 600oC to oxidise all organic matter. Ash was determined by weighing the resulting inorganic residue.

Statistical analysis

The data of the experiments were analysed statistically by the Descriptive Statistics procedure of Minitab Software Release version 13.1 (Minitab 2000)

Results

Biomass production from shrubs of different heights is shown in Table 1. No Melastoma shrubs higher than 2.9 m were found in the field. The total biomass production of edible foliage was highest from shrubs below 1.0 m and between 1 m and 1.9 m. At those heights biomass of edible foliage was 1.5 times higher than biomass of woody stem. Melastoma of the height 2.0 m to 2.9 m had about 3.2 times higher amount of biomass of woody stem than of edible foliage. DM and ash of both edible foliage and woody stem increased with increasing height of the plants.

The re-growth of different height classes of the shrubs is presented in Table 2. The higher shrubs had a higher number of woody stems. The young shoots regenerated well after cutting and grew fast from the second branches and main stems. However, some of shoots did not develop and died and the number of shoots was therefore reduced by time. Six months after the cut surviving shoots still developed well and number of shoots was higher than at the original cut. Sub-shoots also grew well.

Estimated biomass production per hectare (fresh basis) is shown in Table 3. The total fresh biomass yield per ha was about 37.2 tons. The biomass of the edible part of Melastoma was about 22.3 tons/ha and the remaining woody stem was about 14.9 tons. The weight of the fresh biomass of edible foliage was 1.5 times higher than the fresh biomass of woody stems.

Discussion

Plant density and harvest management (age at first harvest, height, and frequency of cutting and season of harvest) are factors that affect the foliage yield (Ivory 1989). In this study, the edible foliage yield in DM from shrubs below 1.0 m and from 1.0 m to 1.9 m was higher than the DM yield of the woody part. Thus, it seems that Melastoma shrubs should be harvested at heights below 2 m to get more edible foliage.

The number of shoots produced was high after one month of cutting. A possible reason for this abundant regeneration may be the time of harvest. The shrubs were harvested in May, which is the start of the rainy season. This time was suitable for re-sprouting due to available moisture, which facilitated recovery after harvesting. Pawlick (1989) also showed that the best time to start re-growth was before the onset of the rains. When the number of shoots increased, the shoots became shorter. It is possible that there was an increasing competition for available resources (light, water, and nutrients) among the shoots at high shoots densities. Thus, shoot numbers decreased with time. The researches on the re-growth of some bush species reported that the regeneration following clearing by slashing was rapid (58% cover after 16 months). That was explained by the high potential of vegetation re-growth of some tropical bush species (McLaren and McDonald 2003).

For estimating biomass production per ha, the twenty subplots of Melastoma shrubs selected to be cut for measuring fresh biomass yield was relatively equal in height at less than one year old ranging from 9 to 12 months of age. Most of the trees at the time of harvest redeveloped after farmers cut for fuel wood during the last dry season. The typical plant community of Melastoma at the study site also included Commelina communis L.,Imperata cylindrica P. Gaernt, Sacciolepsis interrupta (Willd) Stapf, Lygodium flexuosum (L.) S.W. In Schrad, Stenochlaena palustris (Burm) Bedd, Scleria rugosa, R. Br., Scleria sumatrensis, Retz., and Annona glabra, L.. These plants occupied about 20% of the area and are also tolerant towards acid soils. Similar plant communities can be found on the fallow and arable lands in Hoaan in lowland and acid soil areas. Melastoma has relatively high total biomass yield on fresh basis (37.2 tons/ha) and the edible foliage yield was about 60% of the total yield. It may be that these plants have adapted well in the area and possibly also interact with each other when competing for light and nutrients. Man et al. (1995) reported that when growing Gliricidia sepium, Leucaena leucocephala, Acacia mangium from seedlings and applying goat manure and crop residues before planting (5 tons/ha) in pits and also adding chemical fertilizers (60 kg P₂O₅ and 40 kg K₂O/ha) each year, total green biomass yields (ton/ha) in 3 harvests up to 16 months after planting were 28.4, 9.9, and 20.7 tons/ha, for Gliricidia sepium, Leucaena leucocephala, Acacia mangium, respectively. Man and Hao (1993) showed that the ratio of edible foliage gradually reduced with the age of the trees; after planting 5 months, the ratio of edible part of Gliricidia sepium, and Acacia mangium was 75.9% and 80.0% of total biomass harvested but this proportion was only 57.5% and 58.6% at 1 year growth when applying 5 tons/ha organic manure and 60 kg P ₂O₅ + 40 kg K₂O/ha (chemical fertilizers) in the first year and applying chemical fertilizers in the second year.

Photo 1. Melastoma in the field	Photo 2. Re-growth of Melastoma after cutting

Conclusions

• The height of the shrubs at the time of harvesting strongly influenced the yield of edible foliage and woody stem from naturally growing Melastoma.
  
  
• Melastoma shrubs below 2.0 m had the highest edible DM yield in percent of total biomass yield.
  
  
• Plants higher than 2.0 m were more suitable for fuel wood. After cutting, the number of shoots and sub-shoots was higher than stumps and the shoots grew well.
  
  
• Melastoma seems to have a good biomass production but to be able to find a suitable management system different harvest intervals and growth during the dry season needs to be studied.

References

AOAC 1990 Official Methods of Analysis, 15^thn> editon. Association of the Official Analytical Chemists, Washington D.C.

Anonymous 1995 A Diagnosis of the Rained Farming Systems in Coastal Area in Bac Lieu, Minh Hai province: A PRA study, RAFSA/FARM program-FAO, 1995. The Mekong Delta FRS and D Centre, University of Cantho in Cooperation with Minh Hai Extension Centre.

Dung N N X 1996 Identification and evaluation of noncultivated plants used for livestock feed in the Mekong Delta of Vietnam. MSc thesis in the programme "Tropical Livestock Systems". SLU, Department of Animal Nutrition and Mangement, Uppsala, Sweden.

Ivory D A 1989 Major characteristics, agronomic features and nutritional value of shrubs and tree fodders. In: Shrubs and tree fodders for farm animals . Devendra, C. (Ed.), IDRC-276e, Ottawa, Canada, pp. 22–38.

Man N V and Hao N V 1993 Effect of plant spacing on the growth and yield of four legume trees in the grey soil of eastern south Vietnam. Livestock Research for Rural Development. Volume 5, Article #1. http://www.lrrd.org/lrrd5/1/man.htm

Man N V, Hao N V and Tri V M 1995 Biomass production of some leguminous shrubs and trees in Vietnam. Livestock Research for Rural Development. Volume 7, Article #2. 7:2. http://lrrd.org/lrrd7/2/8.htm

McLaren K P and McDonald M A 2003 Coppice regrowth in a disturbed tropical dry limestone forest in Jamaica. Forest Ecology and Management 180, 99-111.

Minitab 2000 Minitab Reference Manual, Release 13.1 for Windows. Minitab Inc., USA.

Pawlick T 1989 Coppice with care. Agrofor. Today 1, 15-17.

SIDA-SAREC 1993 Soil survey Report. Problem Soil Project. Cantho University.

Received 12 April 2016; Accepted 27 April 2016; Published 2 June 2016

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