Vegetative propagation capacities and effect of fertilization on biomass production of Trichanthera gigantea

The multi-purpose tree Trichanthera gigantea was introduced into Vietnam from Colombia in 1990. It does not produce viable seed and must be propagated by asexual reproduction. Studies were carried out on different methods of establishing the tree (using brown or green stem cuttings, or the growing points) and on the response to N fertilization.

Vegetative propagation capacity by planting the growing points was much greater (70 surviving plants produced in 180 days from one "mother" plant) than from brown (3.4 plants) or green stalks (28 plants).

There was a linear response in biomass production as N fertilization (from urea) was increased to 240 kg N/ha/year. The optimum level appeared to be 160 kg/ha/year (40 kg N/ha/cut). Biomass production in the dry season was reasonably high, supplying fresh forage also in the transitional periods (November and March).

Several vegetable species are used for animal feeding in Vietnam, such as sweet potato (Ipomoea batatas), Water-spinach (Ipomoea aquatica), Taro (Colocasia esculenta), Azolla (Azolla inbricata) Ameilema (Ameilema keisak) and Oba-mo (Pistica stratioites). Almost all of them grow on water-logged soil, so they are easily infected by diseases and parasites. In addition, as they are seasonal plants, off-season biomass production is reduced in, for example, November and March every year in North Vietnam.

In July 1990 the Animal Husbandry Research Institute (AHRI)(now the National Institute for Animal Husbandry - NIAH) received a number of stalks of Trichanthera gigantea from Colombia. This tree is native to the coffee-growing area of Colombia (Gomez et al 1991) and has the virtue of producing foliage that is readily consumed by pigs (Sarria et al 1994). It readily regrows after lopping and under repeated (every 3 months) harvesting has given fresh matter yields of foliage of the order of 60 tonnes/ha/year (Gomez et al 1991).

After two years of observations, it was clear that the plant could grow well in the hot and humid environment of North Vietnam. In addition to being a good source of fresh fodder in Summer, Trichanthera gigantea also provides biomass both in early and late Winter-Spring, when other vegetable plants have reduced biomass production.

Up to now, Trichanthera gigantea has only been propagated by asexual reproduction, not from seed. No work has been reported on different methods of establishing it. It is also necessary to know how effective is the utilization of N fertilization to get improved production and quality of Trichanthera gigantea.

Young plants were set in a 10 cm deep hole by hand, with 50 x 60 cm spacing between plants. After six months, the plants were cut for the first time at 30 cm above ground level. The stalks and tops from this harvest were not used in the evaluation.

Table 1: Vegetative propagation capacities of Trichanthera gigantea

	Brown	Green	Growing
	stalks	stalks	points

No of original plants	30	30	30
Cuttings/plant
Mean	3.40	30.2	73.3
SE	±0.97	±3.4	±4.3
Survival rate (%)
Mean	100	92.6	95.7
SE	±2.5	±3.2
Young plants
Mean	3.40	28	70.2
SE	±0.97	±3.1	±4.1
Compared to control=1	1	8.23	20.6
Appearance of
3 leaves (days)	30-35	30-35	20-25

After six months of regrowth, half of the plants were cut at 30 cm above ground level and the brown stalks (15 cm lengths) were counted (control). At intervals of 60 days the remaining plants were cut and separated into green stalks and tops. Thus in 180 days (the same period as the regrowth of the control) the plants were cut three times.

All of the brown stalks (control), the green stalks and the tops were placed in seed beds in the nursery under the shade and with adequate moisture. When the young plants showed three pairs of new leaves they were examined for survival rate.

Table 2: Effect of N fertilization on biomass production and chemical composition of Trichanthera gigantea

	----- Level of N, kg/ha/harvest -----
	0	20	40	60

Production, tonnes/ha/cut*
Fresh matter
Mean	5.82	10.7	15.7	18.4
SE	±0.75	±1.25	±2.0	±1.91
Dry matter
Mean	0.96	1.59	2.06	2.35
SE	±0.15	±0.16	±0.11	±0.11
N x 6.25
Mean	0.113	0.203	0.296	0.363
SE	±0.029	±0.035	±0.039	±0.035
Composition, %
Dry matter, %	16.5	14.9	13.1	12.8
N x 6.25 in DM, %	11.8	12.8	14.4	15.4

A field experiment was conducted at the institute on the typical alluvial soils of the Red River Delta to evaluate response to N fertilization. In this region, the rainy season extends from April- May to September, when 90% of the annual rainfall of 1680 mm falls. January is the coldest month of the year, with a mean temperature of about 16-17 degrees centigrade. There is a little rain from February to March.

The planting method was as stated above. The amount of N (as urea) was: 0, 20, 40, 60 kg N/ha/harvest. Harvesting intervals for fresh forage were 70 days in the rainy season and 140 days in the dry season.

Table 1 shows that in six-month old plants of Trichanthera gigantea there was an average of only 3.4 brown stalks, of which 3.4 survived to form new plants (100%). By contrast, the green stalks and growing points produced from three harvests during the same time period of 180 days were on average 30.2 and 73.3 cuttings/plant with 28 (93%) and 71 (96%) surviving to form new plants. The vegetative propagation capacities of brown stalks, green stalks and growing points were thus 1, 8.23 and 20.63, respectively.

Using asexual reproduction of the growing points, thousands of young Trichanthera gigantea plants were produced and distributed to farmers in several provinces in North Vietnam.

Fresh matter, dry matter (DM) and crude protein (N x 6.25) yields of Trichanthera gigantea responded to increasing amounts of nitrogen applied, but the concentration of DM in fresh biomass decreased (Table 2). Efficiency of utilization of N fertilizer (increment in N in forage/100 kg N fertilizer applied) was: 72, 73 and 67, for the 20, 40 and 60 kg N/cut levels. It appears that about 40 kg N/ha per cutting is the optimal amount for efficient N use by Trichanthera gigantea also for protein content in the DM.

At the 40 kg N level/cut (160 kg N/ha/year), biomass production of Trichanthera gigantea was 63 tonnes fresh matter/ha/year, equal to 8.24 tonnes DM, with a DM content of 13.1% and crude protein of 14.4% (Table 2). The yields of Trichanthera gigantea varied for the period of the year (wet season of about 200 days and the dry season of 165 days). DM yield in the wet season was 5.5 tonnes/ha (67% of the annual total) and in the dry season was 2.74 tonnes/ha (33.3% of the annual total). Biomass production per day in the dry season (16.6 kg/ha) was 60.4% of that of the wet season (27.5 kg/ha). This means that Trichanthera gigantea can give high biomass yields even in the dry season in North Vietnam, especially in the transitional periods (November and March).

Based on the results obtained in these trials, the main conclusions are as follows: