Effect of plant spacing on the growth and yield of four legume trees in the grey soil of eastern south Vietnam
Ngo Van Man and Nguyen Van Hao
Animal Nutrition Department. University of Agriculture and Forestry (UAF). Thu Duc, Ho Chi Minh City, Vietnam.
Four species of legume trees : Erythrina variata (spiny cultivar), Erythrina variata (spineless cultivar), Acacia mangium and Gliricidia sepium were planted at 3 spacings (50 x 50 cm, 50 x 100 cm , 100 x 100 cm) in an experiment carried out on the podzod soil on An Phuoc State farm in Dong Nai province. Seeds of Acacia and Gliricidia and cuttings of Erythrina were established in nurseries 1.5 months before planting on June, 7th 1990. 5 tonnes/ha organic manure, 60 kg P205 + 40 kg K20/ha were applied in the first year, and 60 kg P2O5 + 40 kg K2O /ha were applied in the second year. The results at the end of the rainy season (5 months after planting) indicated planting with a spacing 50 x 100 cm gave the same accumulated green matter yield in the first year as with spacing 50 x 50cm and required fewer seedlings. Acacia mangium was the best in production of biomass (mean green yield 14.6 tonnes/ha) but was low in nutrient content and in sacco degradability in the rumen of cattle. Erythrina, planted from cuttings, could not stand the 6 months continuous dry season: 92% of the plants died during this period. The recoppicing capacities of Acacia mangium and Gliricidia were very good. Cutting at 2 months after the rainy season in the second year the green yield of Acacia mangium was greater than Gliricidia (27.2 tonnes/ha versus 13.3 tonnes/ha). Planting with a narrower spacing of 50 x 50 cm gave a good biomass yield with recoppicing of Gliricidia but had no significant effect for Acacia mangium.
KEY WORDS: Spacing, leguminous trees, grey soil, VietNam, firewood, living fence , alley cropping, Gliricidia sepium, Acacia mangium, Erythrina variata
There is much interest at the present time in the use of legume trees as multipurpose sources of feed, fuel and environment protection (Dale 1987; Preston 1990, 1991). For a long time, farmers in Eastern South Viet Nam have grown many kinds of legume trees for reforestation, animal feed, sources of wood or firewood, shading and as living fences (Bui Xuan An and Ngo Van Man 1980; Duong Duy Dong 1990; Duong Thanh Liem et al 1980; Nguyen Van So 1990). Among them, Acacia auriculiformis, Gliricidia sepium, Erythrina variata are very common. This experiment aimed at assessing biomass production of legume trees that can be used as sources of green manure for alley cropping in the poor sandy soil or fodder for animal production in this region .
The experiment has been carried out at An Phuoc State Farm, Dong Nai Province. The climate is tropical moonsoon with an average yearly rainfall of 1450-1600mm, most of which occurs from May to November. Mean temperature is 26-28 °C, while air humidity varies from 65 to 85%. The characteristics of the top soil are shown in Table 1. It is a sandy acid soil, very low in fertility and reserved mostly for reforestation (Nguyen Thuc Huyen 1980).
|Table 1 : Soil characteristics of the experimente site|
|Soil depth||Texture (%)|
|Cation exchange (meq/100g)|
Experimental location: Anphuoc State Farm.
Experimental factors (treatments): 2 factors:
Legume tree species:
Experimental design: Split plot in randomized complete block; 3 replicates
Planting time: June 1990
Planting method: Seed of Acacia and Gliricidia and cuttings of Erythrina were established in nurseries on April 24th and transplanted on June 7th.
Gliricidia and Acacia mangium seedlings had good establishment; almost 100% of seedlings survived after planting. Erythrina seedlings prepared from cuttings had a high mortality rate because of the apparent weakness of the seedlings.
|Table 2: 2. Surviving seedlings ratio (%) at 30 days after planting|
abc Means in columns (spacing) or in rows (species) without letter in common differ P<.05
|Table 3: Height growth rate (cm/two weeks) of the trees|
|Plant spacing (cm)|
The results indicate that the main factor (planting spacing) had no effect on the height growth rate. The difference in growth rate between Erythrina (spiny) and other plants was significant (P<.05). There was no difference in growth rate among the 3 remaining species: Gliricidia, Erythrina (spineless) and Acacia mangium.
|Table 4: Total accumulated fresh matter yield(ton/ha) at 5 months after planting (end of rainy season)|
The results of the total accumulated fresh matter yield at 5 months after planting indicate that the difference was significant between the spacing 100 x 100 and other spacings. There was no difference between the spacing 50 x 100 and 50 x 50. Planting with a spacing 50 x 100 cm, the green yield accumulated on the first year is as same as with spacing 50 x 50 cm but it saves on the amount of seedlings.
Among the 4 species grown on Anphuoc State Farm, Acacia mangium and Erythrina (spineless) were superior producers of total green biomass than Gliricidia and Erythrina (spiny). It is interesting to note that Leucaena leucocephala grown in the same soil (Ngo van Man and Nguyen Phuc Loc 1985) gave only one third of the yield of Acacia mangium.
|Table 5: Total fresh matter yield (tonnes/ha) at the 2nd and 3rd harvests|
|2nd harvest (1st regrowth; 2 months after beginning of rainy season)|
|3rd harvest (2nd regrowth; 2 months after the first)|
In the second year, at the 2nd harvest (first regrowth) only Gliricidia and Acacia were still growing in the experimental plot. There was a significant difference in green yield in favour of Acacia mangium. Both cultivars of Erythrina died due to the drought in the dry season. Acacia mangium displayed a very good capacity for drought tolerance and growth in the dry season.
The effect of spacing was very clear on the total green yield of Gliricidia, with highest yields for the closest spacing. Spacing did not affect the yield of Acacia mangium.
In the second regrowth (two months after the first), there was no difference between the two species in total green matter yield.
|Table 6. Total accumulated fresh matter yield (tonnes/ha) after one year's growth after planting|
|Mean for spacing||27.5||34.7||20.3|
The results indicate that Acacia mangium was the most productive in the experimental period. It can grow continuously even in the dry season, while other species stopped growing or died. Acacia mangiun, planted with a spacing 50 x 100 , gave the highest yield of fresh matter after one year.
|Table 7. Ratio of edible material (as % of total biomass harvested)|
|Gliricidia||A. mangium||E. spiny||E.spineless|
|5 months after planting||75.9ab||80.0a||72.6b||64.5c|
|1 year growtn||57.5||58.6|
At the harvest 5 months after planting A. mangium had the highest ratio of edible material. At subsequent harvests there were no differences among the species. The ratio of edible material decreased gradually with the age of the trees.
|Table 8. Dry matter percentage of the succulent material of 4 species|
There was no effect of the main treatment (planting spacing) on the dry matter percentage of the edible plant material. Acacia mangium had the highest DM content of the 4 species, followed by Gliricidia and Erythrina. There was no significant difference between Gliricidia and Acacia, nor between the two cultivars of Erythrina.
|Table 9. Nutrient analysis (air dry basis) of the succulent material of the plant biomass 5 months after planting|
CF: Crude fiber, EE: Ether extract
The crude protein of Acacia mangium was a little lower than for the other species and the fibre content a little higher. There was no difference in nutrient content between the 3 species: E. spined, E. spineless and Gliricidia.
|Table 10: In sacco degradability (%) of dry matter (DM) and organic matter (OM)in the rumen of cattle after 48 hours|
The in sacco degradability of the Acacia mangium was very low compared with the other species.
Discussion and conclusion
The results on the survival rate of the seedlings indicate that for having a good establishment of legume trees in sandy upland soils we must prepare seedlings from seeds in a nursery garden before the planting time. Seedlings from cuttings cannot penetrate deeply into the soil, thus decreasing their drought tolerance ability. This was confirmed once again in the dry season. The results from the observations on January, 7th 1991 indicate that all of the Erythrina trees lost all their leaves, while Acacia and Gliricidia grew continuously. At the observation made on May 27th 1991 at the beginning of the rainy season, 92% plants of the two cultivars of Erythrina had died. Acacia mangium was the best in producing biomass in the dry season, and was still green and growing throughout the dry season.
There was very little difference between species in nutrient content according to chemical analysis but there was a big difference in sacco degradability between Acacia and the other species. This is also an indication about the decomposing ability of Acacia leaf, as its leaf is very slow to decompose in the top soil.
Concerning yield of conserved leaves for feeding to animals in the dry season, Acacia mangium is the best of the 4 species tested in the experiment, followed by Gliricidia. However, there may be some limiting factors in the leaf of Acacia mangium. In the feeding trial with Acacia mangium fed to heifers carried out at An Phuoc (Bui et al 1991) in the dry season 1990-1991, the amount of Acacia leaves in the ration eaten the by heifers decreased to 1% of live weight from 2% at the beginning of the trial.
So for choosing leguminous trees to use as a source of fodder, Acacia mangium could be the best, but more trials for improving its nutritive value are necessary. More efforts are also needed in collecting and evaluating new leguminous trees from different localities.
We would like to thank the TCP-FAO (VIE/8954) and SAREC (S/2 VIE 22) for financial support for the experiments.
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(Received 1 March 1993)