BRIDGING THE RICE YIELD GAP IN VIETNAM - Bui Ba Bong^*

^* Cuu Long Delta Rice Research Institute, Omon, Cantho, Vietnam.

Vietnam has 33 million ha of land, of which 7 million ha are agricultural land and rice occupies 4.2 million ha. Rice is the staple food of the Vietnamese people providing 80 percent of the carbohydrate and 40 percent of the protein intake in the diet. It is the predominant crop in most of the ecological regions of the country (Table 1). The sown area was 7.5 million ha in 1998 producing 30 million tonnes of paddy (Table 2). The national average yield is 4 t/h. During the last 10 years the rate increases per year of rice production, sown area and average yield in Vietnam were 5.3, 3.0 and 3.5 percent, respectively. Thanks to the continuous increase in rice production, Vietnam could supply rice to the world from 1989 and has now become the world’s second largest rice exporter. The quantity of rice exported reached 3.8 million tonnes in 1998 (Table 3).

Table 1. Production of Major Crops in Vietnam (1997)

Crop	Area planted (thousand ha)	Yield (t/ha)	Production (million tonnes)
Rice	7091	3.90	27.6
Maize	659	2.49	1.6
Soybean	100	1.02	0.103
Peanut	251	1.40	0.353
Sweet potato	267	6.14	1.6
Cassava	239	8.31	2.0
Sugarcane	251	45.5	11.4
Tobacco	28	1.00	0.28
Cotton	15	0.75	0.14
Coffee	270	1.48	0.400

Source: General Statistical Office (1998)

Table 2. Trends in Rice Production, Area and Yield in Vietnam (1988-1998)

	1988	1994	1995	1996	1997	1998	Increase % per Year (1988-98)
Harvested area (million ha)	5.7	6.6	6.7	7.0	7.1	7.5	3.0
Yield (tonnes/ha)	2.90	3.56	3.69	3.77	3.90	4.0	3.5
Production (million tonnes)	17.0	23.5	25.0	26.4	27.6	30.0	5.3

Source: General Statistical Office (1998)

Table 3. Rice Export from Vietnam (1989-1998)

Year	Quantity Exported (million tonnes)	Value (thousand US$)	Average Price (US$/tonne)	Quality of Exported Rice (%)
				High	Medium	Low
1989	1.372	310	226	0	2.5	97.5
1990	1.478	275	186	14.3	8.7	77.0
1991	1.016	229	225	35.0	10.0	55.0
1992	1.953	405	207	40.3	15.2	44.5
1993	1.649	335	203	51.2	21.4	27.4
1994	1.962	420	214	51.2	21.4	27.4
1995	2.025	538	266	70.0	13.0	17.0
1996	3.047	868	285	54.8	22.7	22.5
1997	3.680	900	242	44.0	8.0	38.0
1998	3.793	1006	266	53.0	11.0	36.0

Source: Ministry of Commerce, Vietnam

Table 4. Area and Average Yield (t/ha) in Different Rice Crops in Vietnam (1994-1997)

Crop	Area (thousand ha)				Yield (t/ha)
	1994	1995	1996	1997	1994	1995	1996	1997
Spring Rice	2381	2421	2541	2682	4.41	4.43	4.80	4.96
Summer Rice	1577	1742	1984	1866	3.57	3.73	3.47	3.51
Autumn Rice	2640	2601	2478	2542	2.80	2.97	2.95	3.06

Table 5. Popular High yielding Rice Varieties in the Mekong Delta of Vietnam (1998)

Variety Name	Origin	Duration (days)	% Harvested Area of 2.5 million ha
IR50404-57	IRRI	95	15
OMCS94	IR59606-119 (IRRI)	95	14
OM1490	OM606/IR44592	90	12
OM1706	OM90-9/OM33-1	95	8
IR64	IRRI	105	10
OM1723	OM554/IR50401	95	10
IR56279	IRRI	95	5
IR66707	IRRI	105	5
OM997	OM554/IR50401	95	8
IR9729-67	IRRI	95	3
IR62032-189	IRRI	105	1
OMFi1	MRC19399 (Philippines)	105	0.9
OM1633	NN6A/IR32843	95	0.7
OM1271	OM89/IR68	95	0.7

Table 6. Improved High-yielding Rice Varieties in the Red River Delta (1998)

Variety Name

U14, U17, U20, P1, Xuan 11, CR103 (IR8423), C70, C71, TK90, X20, NR11, X21, CR01, X33, VN10, DH6, DT10, DT11, DT13, DT33, D271, CM1

Table 7. Hybrid Rice Production in Vietnam, 1992/96

Years	Area (ha)	Yield (t/ha)	Production (tonnes)
1992	11,340	6.60	75,52
1993	34,828	6,71	233,69
1994	60,007	5,84	350,44
1995	73,503	6,14	463.40
1996	102,800	6.58	677,40

Rice is grown in three major ecosystems a) irrigated and intensive b) rainfed and flood prone and c) upland. The irrigated and intensive ecosystem occupies 60 percent of the rice land, while the rainfed and flood prone and the upland ecosystems occupy 32 and 8 percent, respectively.

2. RICE ECOSYSTEMS

In Vietnam, rice is grown in almost all ecological regions with variable topography and the growing areas lie within the tropics (8° N-23° N; 15° S). In the southern delta, the climate is warm-humid all year round with ample sunshine. The northern delta is in the tropical monsoon area with cold winters. The highlands in the north have cool summers and bitterly cold winters, while the highlands in the central region are cool all year round with a long dry season. The central coast of the country has a mixture of northern and southern climates. These characteristics create diversity in rice culture separated by three distinct ecosystems: irrigated and intensive, rainfed and flood-prone and upland.

2.1 Irrigated and Intensive Ecosystem

Irrigated areas lie mainly in the Red River Delta of the north and Mekong River Delta of the south. In the Red River Delta, rice is cultivated with other upland crops in various cropping patterns. In the lowland irrigated areas, two rice crops or two rice crops plus one upland winter crop are planted. In the Mekong River Delta, most irrigated areas are planted to two rice crops: winter-spring and summer-autumn and in some areas three rice crops per year are grown. The yield in the irrigated systems reaches 6-7 t/ha in dry season (spring) and 4-5 t/ha in wet season (summer).

2.2 Rainfed Lowland and Flood-prone Ecosystem

In the past, Vietnam had 300,000 ha of the floating rice in the Mekong River Delta (water level is as deep as 3 m at flowering time). But since 1983, these areas were converted to irrigated areas with 2-3 rice crops pear year when the new canals were constructed. In the Mekong Delta at present there are some 600,000 ha of medium-deepwater with floodwater depths of 30-100 cm. Most of the rice is rainfed, and is unlikely to be replaced by irrigated rice because of the limitation of freshwater resources. Traditional varieties are grown which are photoperiod sensitive, with a yield range from 2.5 to 4.5 t/ha. In shallow rainfed lowlands, improved varieties of medium growth duration (130-150 days) are planted. Yield levels of 5-6 t/ha could be obtained. The yield is usually affected by the water depth. A sampling survey showed that the average yield was 3.05 t/ha for <40 cm water depth, 2.76 t/ha for 40-80 cm and 2.14 t/ha for depths around 80 cm.

2.3 Upland Ecosystem

Upland rice in Vietnam is grown in about 0.45 million ha. This comprises 8 percent of the total rice area in the country. It is grown by 54 ethnic groups of which 50 groups practice shifting cultivation. The total affected area represents about 8 million ha where some 3 million ethnic minorities live. The usual range of annual rainfall is 1,400-1,800 mm but it is very erratic and droughts are common. Slash-and-burn shifting cultivation is the predominant cultivation system. Rice is planted using a stick with 5-10 seeds/hole and holes are dug 20-30 cm apart. Almost no fertilizers or chemicals are used. The yield varies from 0.6 to 2.0 t/ha. After 2-3 years, the farmers abandon the land and move to a new location for planting. Traditional varieties are planted, most of which are sticky varieties, and maturity duration is often in the 130-160 day range. Land degradation and poor soil fertility are serious problems in the upland ecosystem.

3. YIELD GAP AND STRATEGY TO NARROW THE YIELD GAP IN MAJOR RICE ECOSYSTEMS

3.1 Irrigated and Intensive Ecosystem

Problems:

· Stagnant yields in irrigated lowlands.

· Biotic stresses, for example: sheath blight, blast, bacterial blight, brown plant hopper, stem borer, thrips, and leaf-folder.

· Abiotic stresses, for example: acid sulphate soils, salinity, and drought (in rainfed lowlands).

· Lack of early maturing high yielding varieties.

· Low seed yields of hybrid rice.

· Too few parental lines for developing hybrids for Vietnam.

· Too few heterotic hybrids suited to the Red River and Mekong River deltas.

· Poor grain quality of inbreds and hybrids.

· Breeding of high yielding varieties of various maturity groups and good grain quality, including scented rice.

· Breeding high yielding hybrid rice, adaptable to the Red River and Mekong River deltas and possessing acceptable grain quality.

· Breeding of genetically diverse parental lines (cytoplasmic male sterility and temperature-sensitive genetic male sterility - CMS and TGMS) to develop hybrid rice.

· Developing hybrid rice seed production technology.

· Management strategies for durable pest resistance that account for varietal diversity, crop nutrition, cultural techniques, and integrated pest management (IPM).

· Quantifying nutrient balances for present and future productivity levels.

· To sustain rice yield with no symptoms of yield decline or declining factor productivity, and with high output-input ratios.

· To achieve an average annual increase of 3 percent in rice yields for more stable productivity. By 2005, the average rice yield in irrigated areas would be 5 t/ha per crop.

· Meeting the needs of domestic and international customers with varieties of high quality grain.

· Development of a hybrid seed industry resulting in the generation of rural employment opportunities.

Problems:

· Soil problems: acid sulphate soils and saline soils in the Mekong River Delta and degraded soils in the Red River Delta.

· Erratic distribution of water, drought in the early season and the severity of flooding in the latter part of the wet season.

· Insect pests and diseases: stem borer, brown plant hopper, bacterial leaf blight.

· Breeding for varieties with tolerance to abiotic stresses.

· Improved soil management for different types of acid sulphate soils, particularly use of phosphorus; toxicity thresholds for rice and screening for phosphorus efficiency and iron and aluminum toxicity.

· Organic matter management and sustainable agriculture on degraded soils.

· Upland crops in rotation with rice in single-rice cropping areas to increase water-use efficiency.

· Rice yield could be increased by 0.5-1.0 t/ha per crop.

Problems:

· Soil degradation and erosion; low soil fertility; subsoil acidity; low availability of phosphorus and potassium; lack of organic matter; and lack of nitrogen.

· Irrigation not available; and frequent droughts.

· Lack of improved (high yielding) varieties adapted to the diversity and variability of the uplands; limited number of crop species suitable for upland ecosystems; weeds; blast; nematodes; and rice bugs.

· Varietal improvement: Evaluation of traditional cultivars collected and identification of traditional cultivars tolerant to drought and phosphorus deficient soils, resistant to blast and nematodes, tolerant to soil acidity, and with good competitiveness for weeds. Improved germplasm to be introduced.

· New tools for ecosystem management: Crops, hedgerows, and cover crop species tested and evaluated for their efficiency in protecting the soil surface from erosion and preventing pest and disease buildup; appropriate farming systems including integration of livestock and fish culture. Pest and disease management developed; management practices of crop residues tested and evaluated for their effects on the long-term management of organic matter and phosphorus; and new weeding tools developed.

· Improved productivity in the uplands, expected yield to be increased by 1 t/ha.

In the coming years, to meet the increasing food demand of the population (from 76 million in 1998 to 100 million in 2010), rice production in Vietnam should be steadily increased. The area under rice production will not be expanded in the future because the land that can be reclaimed for rice growing is very limited and requires heavy investment. Therefore, Vietnam must carefully preserve rice land and concentrate intensification on narrowing the yield gaps in all the rice ecosystems. This would help to increase the rice yield from the present level of 4 t/ha to 5 t/ha by 2010 corresponding to an increase in rice production from 30 million to 37-38 million tonnes.