Effect of shade on biomass production and composition of the forage tree Trichanthera gigantea

Nguyen Thi Hong Nhan, Nguyen Van Hon, Vo Van Son,
T R Preston¹ and Frands Dolberg²

Department of of Animal Husbandry, Faculty of Agriculture,
Cantho University, Cantho

Abstract
The hypothesis to be tested in the present study was that the biomass yield of the multi-purpose tree Trichanthera gigantea would be enhanced by growing it under partial shade in association with either bananas or the legume tree Leucaena leucocephala. Two experiments of split-plot design were carried out. In the first experiment, the comparison was between partial shade from bananas (at 5 m spacing) or no shade. In the second experiment, partial shade from Leucaena leucocephala (5 m spacings) was included as a third treatment.

A higher proportion of the Trichanthera cuttings germinated in the shade than in the “sun”. The biomass yield of Trichanthera was higher when it was associated with bananas than when planted alone or in association with Leucaena. The absence of effect of the Leucaena may have been because the canopy of this tree is more “open” than in the case of the bananas hence the shade effect was less. There were no significant differences for biomass yield of Trichanthera between plant densities of 20 and 25 thousand plants/ha. On the basis of harvests every 3 months, the observed yield (10–12 tonnes fresh biomass/ha/harvest) in the associations with bananas is in the range of 40–50 tonnes fresh biomass/ha/year.

Key words: Tríchanthera gigantea, bananas, Leucaena leucocephala, shade, associations, biomass

Introduction
Increasing attention is being given to new protein sources, such as the leaves of multi-purpose trees and water plants, in the search for alternatives to conventional protein supplements for both ruminant and monogastric livestock (Gomez et al 1996). Development of these plants as animal feed is also compatible with the strategy for promoting sustainable use of natural renewable resources requiring minimum external inputs (Preston and Murgueitio 1994). The multi-purpose tree Trichanthera gigantea, native to the coffee-growing region of Colombia, is of particular interest as the leaves appear to contain few anti-nutritional compounds (Galindo et al 190) and are readily consumed by pigs (Sarria 1994).

Cuttings of Trichanthera gigantea were introduced into Vietnam in 1991. The tree has been readily adopted by farmers throughout the country because of its tolerance to a wide range of ecological conditions and apparent resistance to pests and diseases (Nguyen Ngoc Ha and Phan Thi Phan 1993; Nguyen Thi Hong Nhan, personal observations).

¹ Finca Ecologica, University of Agriculture and Forestry, Thu due District, Ho Chi Minh City
(E-mail: thomas%preston%sarec%[email protected])
² University of Arhus, Arhus, Denmark (E-mail: [email protected])

Table 1: Effect of shade and spacing on germination and growth of Trichanthera gigantea

# Experiment No

After five years of observations at the Cantho University, it was apparent that Trichanthera gigantea could grow well in the condition of the Mekong Delta, providing biomass in both the dry and wet seasons (Nguyen Thi Hong Nhan, unpublished data). A feature of this tree is its apparent preference for growing under conditions of partial shade. This has been observed in both Colombia and Vietnam (Preston T R and Binh Van Dinh, personal observations).

Table 3: Mean values for biomass yield at the first harvest of Trichanthera planted alone or in association with Leucaena or bananas in experiment 2

The hypothesis to be tested in the present study was that the biomass yield of Trichanthera would be enhanced by growing it under partial shade in association with either bananas or the legume tree Leucaena leucocephala.

Materials and methods

Two experiments were conducted during the period from January to October 1995 in Cantho city where the yearly rainfall is 1600–1700 mm, the mean temperature 26–28°C and the relative humidity 78–88 %. The soil in the experimental area is “sulphate acid” with pH range of 4.06–3.8. The contents of organic matter, N, P and K are low.

Table 2: Effect of shade and planting distance on biomass yield of Trichanthera gigantea in experiment 1

Treatments and design

Experiment 1:
There were two sets of treatments arranged in a 2^*2 split-plot design. The main plots were with and without shade; the sub-plots were planting distances of 100^*40 cm vs 120^*40 cm. The shade was provided by banana trees planted as suckers t 5^*5 m spacing at the same time as the Trichanthera.

Experiment 2:
The treatments in a 3^*2 split-plot arrangement were: shade from banana, leucaena or none (main plots); planting distance of 100^*40cm or 120^*40cm (split-plots). The bananas (as suckers) and leucaena (seedlings from the nursery) were planted 2 months after the Trichanthera. The Trichanthera was established by planting brown stem cuttings in 10cm deep holes. The total experimental area, including protection rows, was 2,500 m².

Management

The Trichanthera was harvested by cutting all the biomass at 70cm above ground level. Yields were recorded for the first two harvests, the first 6 months after planting and the second 3 months later. In experiment 2, the harvested material was separated physically into leaves and stems. Bulked samples from all treatments in experiment 2 were dried at 60°C and subjected to standard proximate analysis. Soil samples from the plots (top 10cm) in experment 2 were taken for standard analysis. There was no irrigation of the plots and no pest control in either experiment.

Results and discussion

Agronomical chacteristics

Mean values for germination rate, plant height at harvest and numbers of branches at 90 and 180 days are shown in Table 1 for the two experiments. A higher proportion of the Trichanthera cuttings germinated in the shade than in the “sun” treatment in Experiment I but there were no differences in Experiment 2. This was probably because in Experiment 1 the banana suckers were planted at the same time as the Trichanthera cuttings, thus providing a degree of shade during the critical second month after planting when the shoots of the Trichanthera began to emerge. In contrast, in Experiment 2, the shade trees were planted two months after the Trichanthera.

In both experiments, the height of the tree at harvest was greater when Trichanthera was associated with bananas, but not with Leucaena (Experiment 2). In Experiment 2, when the branches of Trichanthera were counted, there was a greater number on the banana treatment but no differences due to Leucaena. Density of planting had no effect on any of the parameters.

Table 3: Mean values for biomass yield at the first harvest of Trichanthera planted alone or in association with Leucaena or bananas in experiment 2

Biomass production
The biomass yield of Trichanthera was higher when it was associated with bananas than when planted alone or in association with Leucaena (Tables 2 and 3). The absence of effect of the Leucaena may have been because the canopy of this tree is more “open” than in the case of the bananas hence the shade effect was less. There were no significant differences for biomass yield of Trichanthera between different spacing. If 4 harvests are taken per year then the observed yield in the associations with bananas is in the range of 40–50 tonnes fresh biomass/ha/year, which is similar to the yield data reported by Gomez and Murgueitio (1991).

Nutrient content
The data for nutrient analysis in table 4 indicate that the leaves of Trichanthera are rich in protein, minerals and carotene and relatively low in crude fibre. It was noted that the Trichanthera coppiced rapidly and quickly regenerated new shoots. The regrowth was more vigorous than from stem planting presumably because the plant does not expend nutrients in growing roots.

Trichanthera cuttings were distributed to farmers in several provinces in the Mekong Delta. It was observed that the tree tolerated flooding for periods of up to one month. In severe drought, the leaves died but were quickly regenerated when the rains started. It showed high resistance to pests and diseases. Pseudococcidae has been found recently, that attacks the young plant, but rarely causes serious damage. Once rapid growth begins, Trichanthera forms a dense canopy of foliage that shades out weeds.

Table 4: Chemical composition in DM of Trichanthera gigantea

CP N*6.25;
EE Ether extract;
CF Crude fbre

Conclusions and recommendations

• Trichanthera gigantea is easy to establish in the conditions of the Mekong Delta in Vietnam.
• Growing it in association with bananas leads to increased yields of biomass with no apparent effect on the productivity of the bananas.
• There were no apparent differences in yield between plant densities of 25 and 20 thousand/ha.

Acknowledgements
This research was supported financially by the International Foundation for Science through a grant (B/2231–1) to the senior author.

References

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