Biomass production of some leguminous shrubs and trees in Vietnam

Seven species of legume trees and shrubs: Gliricidia sepium, Leucaena leucocephala, Indigofera teysamii, Acacia mangium, Acacia auriculiformis, Flemingia congesta, and Desmodium ransonii were planted according to a randomized complete block design on the podzol soil of the University experimental farm at Thu Duc, Ho Chi Minh city.

Flemingia and Desmodium were planted by seed; the other species were transplanted by seedlings. Five tonnes/ha of goat manure and crop residues were applied in pits before planting; 60 kg P₂O₅ and 40 kg K₂O/ha of chemical fertilizers were applied each year. One time weeding was done two months after planting. Edible parts of these species were used in an intake trial with a group of young goats.

The results of three harvests in a total period of sixteen months after planting indicated: (i) for biomass production in poor soil, Indigofera teysamii, Gliricidia sepium and the Acacia spp were highest in ranking; (ii) Gliricidia sepium, Indigofera teysamii were the best choice in fodder production for goats. The leaves of the Acacia spp, although with a low digestibility, still play an important role in solving the shortage of grass on poor soils and in a dry zone.

Tropical tree legumes have the potential to produce large quantities of high protein leaf for animal consumption (Blom 1980). This is particularly important in areas where the majority of ruminants are currently fed forages and crop residues of low nutritive value (Preston and Murgueitio 1992). Consequently, many recent studies have examined the effect of supplementing these feed resources with leaves of tree and shrub legumes, such as Sesbania grandiflora (L.) Poir, Calliandra calothyrsus Meissn, Gliricidia sepium (Jacq.) Walp. and Leucaena leucocephala (Lam.) de Wit.

In Vietnam, especially on the Upland grey soils which is a very poor soil in the Eastern part of the South, very little research has been done on planting and management systems appropriate for optimal production of leaf and wood from these tree legumes. Recently, with projects focussing on the sustainability of farming systems and environmental impact, the role of leguminous trees in the farming systems has been emphasized (Preston and Murgueitio 1992; UAF-CSI SALT project, UAF-SAREC project). The staff of the Department of Animal Nutrition and the Farming Systems Research Team of the University of Agriculture and Forestry have carried out some studies for exploiting the role of leguminous trees in supplying a good fodder, an excellent green manure and a stable source of firewood in the system.

The objective of the experiment reported here was to assess the biomass production of some species of nitrogen-fixing shrubs and trees grown on the grey, sandy, and acid soils in the dry land area of the Eastern part of South Vietnam. The experiment is part of a programme to continue studying, evaluating, and introducing the leguminous plants in the farming systems of this region.

The experiment was started in May, 1992 in the UAF experimental farm at Thu Duc, Ho Chi Minh city. The climate is tropical monsoon with a yearly rainfall in the range of 1600-1800 mm, most of which occurs from May to November. The temperature range is 26-28°C. Air humidity varies in the range 65-85%. The soil is sandy and acid, more than 70% sand in the soil texture, very low in fertility and the pH is 4.5-5.0 in the top soil.

Seven species of leguminous shrubs and trees were planted at 0.8 m x 0.5 m spacing in a randomized block design, with eight replicates. The trees/shrubs were: Flemingia congesta, Desmodium ransonii, Gliricidia sepium (Jacq.) Steud (local cultivar), Leucaena leucocephala (Lam.) de wit (acid-tolerant cultivar from Philippines), Indigofera teysamii (local cultivar); Acacia mangium Willd., Acacia auriculiformis A. Cunn. ex. Benth.

Flemingia, and Desmodium (4 replicates only) were planted by seed on 22 May 1992; the other species were planted as seedlings on 10- 12 June 1992. These seedlings were prepared in the nursery on 26 April. Five tonnes/ha of goat manure and crop residues were applied in pits before planting; 60 kg P₂O₅ and 40 kg K₂O/ha of chemical fertilizers were applied each year. One time weeding was done two months after planting. Edible parts of these species were used in an intake trial with a group of young goats.

In the first year, plant height and biomass production were monitored at the end of the rainy season. In the second year, biomass data were collected at the cutting frequency of twelve weeks with samples taken from 3.2 m² area from the top to 60 cm above ground level. The ratio of edible parts and branches of each specie and the dry matter content of each part were monitored. Nutrient content of each species and soil analysis were done by standard laboratory methods.

For evaluating the relative intakes of these species by goats, a cafeteria-type trial was conducted. One group of 5 young bucks was offered a ration of 200 g/head/day of a mixed feed. Elephant grass and leaves from one of the legume trees were offered free choice. Each legume specie was offered during a one week period.

The amounts offered and refused of grass and legume leaves were determined twice daily. The results of the last three days during each test week were used in the statistical analysis.

The results indicate that Indigofera grew the fastest in height. Gliricidia, Leucaena, Acacia auriculiformis grew at a medium rate and Acacia mangium, Flemengia and Desmodium were the slowest. This height growth index represents the capability to compete in the first phase of the growth cycle. If compared with the results reported in an earlier trial (Ngo Van Man and Van Nguyen Hao 1993), the growth rate in height of Gliricidia and Acacia mangium in this experiment was lower. The reason may be the difference in soil fertility of the two sites.

Table 1: Plant height and rate of growth in height

	Plant height	Growth rate
	(cm at 5 mths)	(cm/2 weeks)

Indigofera	127	9.8
Leucaena	102	7.8
Gliricidia	94.3	7.3
A. auriculiformis	95.1	7.3
A. mangium	69.3	5.3
Desmodium	53.2	4.8
Flemengia	49.0	4.5

The results in Table 2 show that during the period from planting to five months Indigofera teysamii was the best in biomass production. The second was Gliricidia sepium. Leucaena leucocephala was the worst. There were no significant differences in biomass production among the others. Compared with the report of Ngo Van Man and Van Nguyen Hao (1993), the biomass yield of Gliricidia in this experiment was a little higher and Acacia mangium was lower.

Table 2: Green biomass yields (kg/ha) in three harvests up to 16 months after planting

	Harvests
	11/92	6/93	9/93	Total

Indigofera	7,661c	10,385a	15,293c	33,339
Gliricidia	5,436a	9,966a	13,000ac	28,402
A. auriculiformis	1,900bd	17,354c	7,953d	27,207
Desmodium	3,194d	8,836ba	9,609ad	21,639
A. mangium	2,292bd	10,262a	8,148d	20,702
Flemengia	2,688bd	8,352ba	9,359ad	20,399
Leucaena	1,537b	4,326b	4,051b	9,914

Results for biomass yield in the first cutting in the second year (Table 2) indicate that after the six months of dry season and one month into the rainy season, Acacia auriculiformis was the best producer. It may be the best of the group in drought tolerance. The next best producers were Indigofera teysamii, Acacia mangium and Gliricidia sepium. The results for Gliricidia and Acacia mangium are lower than in the earlier experiment (Ngo Van Man and Van Nguyen Hao 1993).

In the third harvest in year two, Gliricidia sepium and Indigofera teysamii were better than the other species in biomass production.

This result confirms that Gliricidia and Indigofera have a strong capability to coppice in the rainy season. The overall production of biomass in slightly more than one year is shown in the last column of Table 2. Indigofera teysamii, Gliricidia sepium and Acacia auriculiformis were the most productive overall. From the standpoint of animal feed, the data in Table 3 indicate that in edible leaf production, Acacia auriculiformis gave the highest yield, followed by Indigofera teysamii, Gliricidia sepium and Acacia mangium with Flemingia congesta being the lowest.

Table 3: Accumulated (3 harvests) production of edible parts and stem (dry matter basis) of seven tree legumes for a 16 months period (5/92-9/93)

	Leaf	Stem	Total
	kg dry matter/ha

Acacia auriculiformis	5,708	2,987	8,695
Indigofera teysamii	5,250	3,173	8,423
Gliricidia sepium	4,510	1,877	6,387
Acacia mangium	4,212	1,267	5,479
Flemengia congesta	3,386	1,358	4,744
Desmodium ransonii	3,604	1,094	4,698
Leucaena leucocephala	2,322	1,330	3,652

The data for nutrient analysis in Table 4 indicate that Indigofera teysamii was the highest in crude protein and lowest in crude fibre. Acacia mangium showed the opposite trend. Indigofera also had a very high content of calcium.

Table 4: Nutrient content of the edible part of the legume tree foliage (Source: UAF Animal Nutrition Department laboratory)

	N x 6.25	EE	CF	Ash	Ca	P
	--------- % in DM ---------

Gliricidia	17.0	7.53	25.2	7.04	0.21	0.03
Leucaena	20.3	6.59	22.9	4.90	0.19	0.05
Indigofera	24.8	4.76	15.2	8.09	2.08	0.27
A.mangium	16.6	4.26	32.4	3.19	0.30	0.35
A.auriculiformis	17.5	NA	22.6	4.03	0.28	0.31
Flemingia	17.9	4.45	23.4	4.95	0.28	0.59
D. ransonii	21.0	5.97	23.5	6.07	0.46	0.33

The data in Table 5 show that Indigofera teysamii had the highest accumulation of nitrogen in the off-ground biomass and also in the edible part (Leaf and young shoots). After that came Acacia auriculiformis and Gliricidia. Indigofera teysamii has been used for a long time by foresters in Vietnam as a reforestation pioneer tree.

Table 5: N accumulated by the trees in three harvests in the period up to 16 months after planting.

	Leaf	Stem	Total
	-- kg N/ha --

Indigofera teysamii	208	41.9	250
Acacia auriculiformis	160	31.4	191
Gliricidia sepium	122	37.7	160
Desmodium ransonii	121	12.0	133
Acacia mangium	112	10.5	123
Flemengia congesta	96.8	16.3	113
Leucaena leucocephala	75.5	14.9	90.4

The data in Table 6 show the relative proportions of the goat ration represented by the edible parts of the legume tree species. Leucaena leucocephala was the most palatable to the goat, followed by Gliricidia sepium, Desmodium ransonii, Indigofera teysamii, Flemingia teysamii and Acacia mangium. As a percentage of the total diet (including the supplement component), the amount of leguminous leaf (on dry basis) varied from 21 to 53%.

Table 6: Proportion of legume leaf fodder consumed by goats as percent of green feed (fresh and dry basis) and as % of total diet.

	Proportion of legume foliage (%)
	-In green feed-		In total diet
	FM	DM	DM

Leucaena leucocephala	47.0ab	69.3a	52.9a
Gliricidia sepium	51.0a	63.7b	41.7b
Desmodium ransonii	44.0b	59.0b	40.9b
Indigofera teysamii	43.7b	53.7c	35.7c
Flemingia congesta	31.0c	43.3e	29.5e
Acacia mangium	21.3d	33.0d	21.6d

After more than 18 months monitoring of the biomass production of seven leguminous species and their relative acceptability by goats, it is possible to arrive at some tentative conclusions and recommendations: