|CERES No. 134 (FAO Ceres, 1992, 50 p.)|
By Le Van Lanh
Beginning in 1961 and accelerating into the early 70s, the Vietnamese government resettled hundreds of thousands of Kinh people from the overpopulated lowlands of the Red River Delta into the "new economic zone" of the midlands' bordering the delta's alluvial plain. The goal was to relieve population pressure, while simultaneously developing a hitherto sparsely peopled region where settlement had been held back, partly by fear of once-endemic malaria.
But the road to ruin is paved with good intentions: in this case the result of migration was increased ecological destruction, which mounted as population rose in the new settlement area to its present density of 500-600 persons/km². The process of land degradation was due partly to the geographical and physical character of the midlands themselves, as well as the slash-and-burn agriculture traditionally practiced by local hill peoples. But the farming practices of the newly arrived Kinh people, which had worked well in the lowlands, were not adapted to their new environment and greatly aggravated the destruction. To reverse the damage, a new development model - based on the "agro-ecosystem" concept - had to be created.
Climate, soil and forests
Vinh Phu is the northern midland province of Vietnam, and is characterized by alternating narrow valleys and rounded hills, with relatively gentle grades of eight to 35 degrees, ranging from 10 to 150 metres above sea level. It has a tropical monsoon climate, the May to October rainy season accounting for 85 per cent of a mean annual rainfall of 1 550 to 2 500 mm. The rain often comes in intense showers of 3.7 mm per minute for 10 minutes. In contrast, the November to April dry season is punctuated by frequent droughts.
Most of the hill soils in the area are yellow and red soils, classified as Oxisols (according to the US taxonomy system) or ferralsols (according to the Unesco-FAO classification). In the valleys, the soils are alluvial and colluvial, or fluvisols according to the FAO classification. Due to high temperatures and humidity, the weathering process is rapid, with a weathering crust a dozen metres thick. Basic washout leads to increasing soil acidity, and clay formation in this acidic environment results in kaolinite clays with low absorption capacity. Iron compounds are dissolved and move freely from place to place, accumulating in the form of concretions and plinthite. On the hillsides, slate clay and metamorphic rocks (phyllite, gneiss, mica slate) are common, and the weathering crust in these rocks is rich in aluminum. Due to erosion it is also poor in alkaline and alkaline-earth metals, with a pH of 4.0 to 5.5. In the surface layer, humus content is one to two per cent, nitrogen 0.05 to one per cent, total phosphorus 0.03 to 0.06 per cent, and total kalium 0.15 to 0.5 per cent. The soil formed on rock (such as sandstone) is typically poor in iron, with bad structure. Soils in the valleys are very acid, and iron toxicity may be a major constraint to rice yields there.
Originally, the province was covered by tropical rainforests, with many strata. The indigenous tribal peoples who lived in the hilly areas practiced mainly Sweden (slash-and-burn) agriculture, clearing and burning forest to make space for growing dry rice, corn, cassava and tea, and rotating their fields every few years with fallow periods to protect soil fertility. This farming system can function well only if populations do not rise too quickly, and adequate fallow periods are maintained. If population pressures lead to shortening of the fallow cycle, land degradation is inevitable.
The influx of lowlanders brought fundamental changes, causing an
ecological imbalance. There are at least six ways to create such imbalances and,
together, local and newly arrived farmers in the midlands employed all of
squandering forest resources through deforestation, by clearing forests for land
reclamation and over-exploiting them for timber, fuel-wood and industrial raw materials;
practicing shifting cultivation with insufficient fallow periods;
mono-cultivating annual crops on sloping land;
using inappropriate cultivation methods to grow perennial crops;
Rapid population growth created increasing demand for fuelwood and food. The clearing of forests, both for wood and new cropland, accelerated, and the burning of dry residues destroyed biological activity in the humus of the soil surface layer. This led to deterioration of the soil structure and increased erosion.
The Kinh, though good soil managers on their home grounds, had little experience in farming hilly areas. Cassava, for example, is the second most important crop in the midlands, next to rice. But the Kinh paid little attention to soil conservation when planting it. When cassava is grown as a monocrop on steep slopes, it provides little protection to the soil under it, which is prone to washing away. A particularly heavy rain ( 170 mm) on 9 April 1982, for example, washed away 200 tons of soil from a single hectare of newly-grown cassava. Because of low soil fertility, cassava production was low, at around three to five tons/ha/year.
Tea is another important cash crop. But tea plantations were neglected and not intermixed with other crops. Such plantations develop slowly and tend to become covered with grasses. The soil is more exposed to the sun, increasing erosion. Overgrazing by livestock on the hills further aggravated the erosion problem.
Meanwhile, the Kinh planted paddy rice in the narrow valleys, where it was frequently destroyed by floods and siltation, caused by the erosion in the hills. Rice productivity remained low, decreasing quickly after the first harvest on new land.
The result of all these errors was severe land degradation, increasingly bare hills and steadily decreasing crop yields.
Accelerated erosion, leaching and degeneration of soil structure
all contribute to degradation. So
does formation of the aforementioned concretions and plinthite from aluminum and iron oxides. This is especially serious in soil formed on ancient alluvial deposits and at the foot of hills, where the ground water table is high. The effect of plinthite is to decrease permeability and increase erosion. The thickness of the soil layer on top of the plinthite zone is crucial to the workability of the soil and plant growth - in some places in Vinh Phu these soil horizons disappeared entirely. This made the land barely usable, lowering crop yields.
Human inroads eliminated most of the primary tree species, leaving only secondary forest made up of such species as Canarium album, Litsea cubeba, Liquidamba formosana, Mangletia glauca, Styrax tonkinensis, Cinanmomum album and Oronsia tonkinensis. Most of the region's vegetation became savannah, with bushes and herbs, including Rhodomyrtus tomentosa, Melastoma candidum, Dieranontesis linear-is and Hedyotis auricularia.
Rehabilitation was possible, but only if it was tailored to the natural conditions of Vinh Phu Province, its topography and soil characteristics, and - of crucial importance - the social factors from which poor practices stemmed. There had to be changes in land use and management, as well as water conservation and control of soil erosion. This involved looking at the complex of people and their environment in terms of interlocking systems - more specifically, the agro-ecosystem concept, described by Kanok Rerkasem in his 1989 paper, Agro-ecosystem and rural resource analysis (the SUAN Secretariat, Farming Systems Research Project, Khon Kaen University, Khon Kaen, Thailand) and in Cuc, Gillogly and Rambo's Agro-ecosystems of the midlands of northern Vietnam (see below).
This approach considers several system properties, but especially productivity and sustainability. It assumes that a system will respond as a whole to a given stimulus or change, even if the stimulus is applied to only one part of the system.
Vinh Phu's problems were confronted on a variety of fronts:
Improving land use - Intercropping was a basic tool. Annual crops were planted with leguminous and green manure plants in such combinations as cassava and peanut, cassava and oregon pea, maize and soybean, cassava and Tephrosia candida. With intercropping, crop yields rose to 12-18 tons per hectare of fresh tuber cassava in fertile soil and 510 tons in degraded soil; 1 800 kilograms per ha of maize grain; 500-800 kg per hectare of peanuts in dry nut form; I 000 kg per hectare of soybean seed. There was a mass of fresh green matter to improve the soil: 19 tons per ha from peanut and 12-18 tons per ha from Tephrosia candida. The soil structure improved as its water-holding capacity and permeability increased, and because the soil was covered, losses caused by water erosion diminished.
Manure was allocated first to rice fields and homegardens. If any was left over, it went to upland fields. Cassava fields received 5.4 to 13.5 tons per ha. Chemical fertilizers were also used, but in relatively small amounts.
Redesigning tea plantations - The redesigning of tea plantations started with planting trees. Tephrosia candida was placed on ridges and hill roads to provide shade for the tea plants and soil cover, preventing erosion, holding moisture and fixing nitrogen. The trees' litter was left on the hill to enrich the soil. Cassia siamea and Vernicia montana were scattered through the plantations at a density of 150 to 200 trees per ha to shade the farmers as well as the plants they were tending.
The tea was planted along the contour of the land in rows 50 centimetres wide on the surface of the soil, 40 cm deep and 30 cm wide under the soil. The young plants were covered with rice straw and dry grasses to maintain soil moisture. Urea was applied at the rate of 50 to 135 kg per ha and phosphorus at the rate of 50 to 270 kg per ha. The plantations can yield about six to eight tons of wet tea per ha over 40 to 50 years, but setting them up is not cheap. The design costs US$500 per ha.
Reforestation - Native trees, including Mangletia glauca, Styrax tonkinensis, Cinanmomum album. Melia azedarach, bamboo, jackfruit, persimmon and Iychee, were used for reforestation. They were intercropped with hill rice, cassava, corn, peanut, soybean and pineapple in the early stages, as in the so-called taungya agroforestry system.
Plantations of fast-growing eucalyptus were developed during the 1980s on large sections of barren hill lands, to provide raw material for the paper mills of Vinh Phu Province. But it was found that the soil under the plantations became compact and dry. It was suspected this was because the fallen eucalyptus leaves contained Cinoel, which inhibits development of both flora and soil micro-organisms. To deal with this problem, starting in the late 1980s, legume trees such as Acacia mangium, Acacia auriculiformis and Tephrosia candida were inter-planted with eucalyptus. In such mixed forests, soil humidity is 20 to 30 per cent higher and the humus content 15 to 25 per cent higher than in forests where eucalyptus grew alone.
Homegardens and the (R)VAC system - The rural landscape of Vinh Phu Province is fairly complex, and the pattern of land use reflects this. The three major elements are (1) valleys between hills, (2) household plots and associated homegardens and (3) sloping uplands. The (R)VAC system, an acronym based on four Vietnamese words, consists of R=rung= forest, which is a new component, V=vuon= gardens, A=ao=fish ponds and C=chuong=animal pens. The government has promoted VAC systems since 1981 in recognition of their contribution to household nutrition. In Vinh Phu Province, each family was given lifetime tenure on 300 square metres for a garden, which they could enlarge by paying taxes on the additional land. (R)VAC makes use of all three elements of the landscape:
(1) In the valleys, the principal land-use systems are paddy fields and water re sources. The paddy fields are on moderately flat, terraced and bounded lowland. Farmers used liming to control soil acidity and intercepted the interflow and sediment to alleviate the problem of iron toxicity. The reservoirs, ponds and streams, found mainly in the valleys, are used for irrigation, aquaculture, care of livestock and washing. The fish raised in ponds and reservoirs provide the household with animal protein, and household and animal wastes may go to feed the fish in the ponds.
(2) The homegarden is located on the lower part of a hillside, planted with vegetables, trees to provide fruit and wood and medicinal and decorative plants. Oranges, lemons, pomelo, grapefruit and papaya were interplanted with tea. Bamboo, rattan and other trees planted at the foot of a hill not only provide wood but serve as a fence, which halts landslides and prevents siltation of fish ponds and reservoirs in the valley.
(3) Upper slopes and hilltops were used for agroforestry, collection of wood for fuel and construction, and some grazing. Indigenous, fast-growing tree species like Styrax tonkinensis and Manglietia glauca were planted along with exotics like Eucalyptus camaldulensis mixed with Acacia mangium and Acacia auriculiformis. At the start of the program, perennial trees were mixed with Tephrosia candida to prevent soil erosion and maintain moisture in the soil.
Lower slopes of less than 35 degrees were devoted to tea
plantations. Slight slopes next to the household plot also tended to be planted
with tea or cassava. The tea was intercropped sparsely with trees like Cassia
siamea and Vercinia montana to provide shade and maintain soil moisture and
Tephrosia candida to fix nitrogen.
Water conservation/erosion control -
Broadly speaking, water conservation is the most important part of soil management. Its objective is to increase water penetration into the soil and the capacity of soil to hold water. This is done by decreasing surface runoff and erosion and providing enough water for crops during periods of drought. This was achieved in Vinh Phu by building reservoirs and maintaining cover on the soil surface.
The reservoirs were important both for the water balance in the upland and for flood control in the lowland. Reservoir water can be used for irrigation during the dry season. It also changes the microclimate around the reservoirs, increasing the moisture in the air, lowering the temperature and raising the ground water level. Vegetation near reservoirs grows rapidly.
The soil was covered by mulching with dry grasses, litter and Tephrosia candida, Styloxanthese gumilis and other leguminous plants, using such multiple cropping systems as intercropping, crop rotation and sequent cropping and preserving natural secondary vegetation in fallow areas.
Tephrosia candida - Tephrosia candida, a leguminous tree that grows as a low shrub, played a key role in rehabilitation, improving soil fertility within two to three years and helping to control erosion and conserve water. It decreased evaporation and lowered soil temperature so that soil moisture increased. It prevented soil loss, supplied organic matter and nutrients and improved soil structure. Along with the characteristics common to all leguminous trees, including the capacity to fix nitrogen, produce seeds prolifically and survive under difficult conditions, Tephrosia candida has leaves of a size useful in agroforestry. Most important, it grows rapidly and well in very dry soil where Leucaena glauca, famous throughout Southeast Asia, cannot grow at all.
Tephrosia candida can produce 12 to 18 tons of biomass per hectare per year when mixed with cassava and 20 to 40 tons, sometimes more, in monoculture. Its biomass makes excellent green manure because of the high nutrient content. When it was planted with food crops on bare hills where other species could not grow, nutrients in the soil increased 30 to 35 per cent and the cassava yield 25 per cent. The tree was also planted to shade young eucalyptus and other plants, and its leaves were left to decompose for nutrients.
Social factors - In planning rehabilitation, it was recognized
that social factors - particularly population pressure and landownership - are
crucial to the use and misuse of land. A national family planning program now
aims at lowering the rate of population growth from the
present 2. 1-2.2 per cent to 1.7 per cent by the year 2000.
Long-term land tenure and tax exemption on degraded land are also being used as incentives for rehabilitation and conservation. This is a new departure for Vietnam. During the Colonial period, most land was privately owned, and many peasants were landless laborers. In the land reform program of 1955-56, the state expropriated land and redistributed it to farmers. In 1960, most of the land in North Vietnam was put under the management of cooperatives and state enterprises, which discouraged farmers from paying attention to soil conservation and improvement of soil fertility.
Since 1989, however, paddy fields, forests and hill land with crops have been allocated to households. Land tenure is 25 to 50 years, encouraging farmers to invest in fertilizer and learn advanced agricultural techniques to increase crop yields.
The results have been generally good. Many farmers have used their lands rationally and raised productivity, although some continued to grow cassava alone on steep slopes and eucalyptus in dry soil, often because of a lack of funds. Farmer income is low and adequate credit is not available, so they cannot always afford to invest in rehabilitating their land.
Overall, however, the ecological models created over the last nine years have won local support. Because the objectives satisfied local needs, local people supported them. Truong Trung, chairman of the provincial Science Committee, gave an enthusiastic report on agroforestry models built since 1986 in the Thanh Hoa, Doan Hung and Lap Thach districts:
"This is a widespread, integrated study concerning the environmental ecosystems, cropping systems and rehabilitation of degraded land in Vinh Phu, which has been accepted and widely applied by local people and highly appreciated by local and international visitors", he said. And, he added, not only did the project result in increased production, it also provided for greater collaboration in science and technology between localities and the government.
Much remains to be done, but what appears to be a successful approach is now established, on which future efforts can build.