Nhâm-Dần 2022

CHALLENGES OF RICE PRODUCTION

IN THE MEKONG RIVER DELTA

Nguyễn Văn Ngưu

A rice field in the Mekong River Delta

1. INTRODUCTION

Cần Thơ gạo trắng nước trong

Ai đi đến đó lòng không muốn về

Or

Cần Thơ has white rice and clear water

Visitor arriving at this place has no wish to return to his old place

Cần Thơ City is the capital of the Mekong River Delta (MRD). The Mekong River reaches the East Sea or South China Sea after crossing China, Myanmar, Laos, Thailand, Cambodia, and Vietnam and the MRD roughly forms a triangle stretching from Mỹ Tho in the East to Châu Đốc and Hà Tiên in the Northwest, down to Cà Mau at the Southernmost tip of Vietnam. The MRD is dominated by flat flood plains in the South, with a few hills in the North and West. The average elevation of the MRD is only about 1 m above mean sea level.

The soil of the MRD consists mainly of sediment from the Mekong River and its tributaries, deposited over thousands of years. Due to its mostly flat terrain and few forested areas, almost two-thirds of the region’s land can be used for agriculture, especially for rice production. The Mekong River Delta (MRD) is often called “Vietnam’s Rice Bowl” because it produces about 50% to 54% of the total Vietnam’s rice production yearly. However, recently, rice production in the MRD faces number of problems due to drought and salinity. These natural problems may become more severe, especially under severe scenarios of climate changes and sea level rise.

2. THE MEKONG RIVER DELTA

The Mekong River Delta (MRD) or Đồng bằng Sông Cửu Long is the region in Southwestern Vietnam where the Mekong River approaches and empties into the sea through a network of distributaries. It encompasses over 40,500 square kilometres and lies immediately to the west of Saigon, roughly forming a triangle stretching from Mỹ Tho in the East to Châu Đốc and Hà Tiên in the Northwest, and down to Cà Mau at the Southernmost tip of Vietnam.

Archaeological discoveries show that the MRD was an important part of the Funan kingdom in the first century AD. Beginning in the 1620s, Cambodian King Chey Chettha II allowed Vietnamese to settle in the area. The increasing waves of Vietnamese settlers slowly Vietnamized the area and in 1698, the Nguyễn Lords sent  a Vietnamese noble, Mr. Nguyễn Hữu Cảnh, to the area to establish Vietnamese administrative structures in the area. This act formally detached the MRD from Cambodia and placed it firmly under Vietnamese administrative control.

Before 1975, Mekong River Delta (MRD) was part of the Republic of Vietnam. Today, the region comprises 12 provinces: Long An, Đồng Tháp, Tiền Giang, An Giang, Bến Tre, Vĩnh Long, Trà Vinh, Hậu Giang, Kiên Giang, Sóc Trăng, Bạc Liêu, and Cà Mau, along with its capital city of Cần Thơ. The Mekong River is divided in Phnom Penh of Cambodia into 2 branches Tiền River and Hậu River. In Vĩnh Long Province the Tiền River is further divided into the Mỹ Tho and Cổ Chiên Rivers and it exists out at sea via 6 estuaries namely Hàm Lương, Ba Lai, Tiểu, Đại, Cung Hầu and Công Hầu. The Hậu River is divided into three branches namely Định An, Bassac and Tranh Đề before existing out at sea.

In flood season, the Mekong River discharge 84% of its water into the Tiền River and 16% to the Hậu River. The overflowed water of the Hậu River flows to Thailand Bay, while the overflowed of the Tiền River flows to Vàm Cỏ River and Đồng Tháp Mười (or Plain of Reeds). In the MRD, there is a high density of canals with a total length of 5,000 km, of which 1,600 km has a width of 18 to 60 m. The most important canals for transportation and irrigation are the Vĩnh Tế, Trí Tôn, Rạch Giá, Cái Bè, Thốt Nốt and Phụng Hiệp. The annual amount of water of Mekong River is about 450 billion cubic meters. Annually the water level of Mekong River is highest in September and then slowly goes down.

The rainfall season in the MRD, as represented by the rainfall in its capital city of Cần Thơ, starts in April and ends in December (Fig.1)

Fig.1 Rainy season (monthly rainfall) in Cần Thơ

The Mekong River Delta (MRD) displays a variety of physical landscapes but is dominated by flat flood plains in the south, with a few hills in the North and West. There are some high strips of land, which is called “Giồng” by local people. The altitude of Giồng is higher than the average altitude of the MRD. The Giồng of Tiền and Hậu Rivers in the North are higher than that in the South. There are also sandy dunes distributed between rivers and 50-60 m away from the sea, which are called Coastal Giồng. Between sandy dunes are lower strips of land with clay soil texture, which are used for paddy rice cultivation.

The soil of the MRD consists mainly of sediment from the Mekong River and its tributaries. About 2.6 million ha in MRD are used for agriculture and over half of the total arable land in the region or 1.7 million hectares of land are being used for rice production. In the MRD, the area for rice cultivation is distributed in 3 soil types: acid sulphate, saline, and alluvial soils. The saline soils are found in Bac Lieu, Ca Mau, Kien Giang, Tra Vinh and Ben Tre provinces; the acid sulphate soils occupy nearly 600 thousands ha in coastal areas of the MRD; and the alluvial soils are found in 850 thousands ha along the Tien and Hau Rivers in the MRD.

3. RICE PRODUCTION IN THE MEKONG RIVER DELTA

Rice production in the Mekong River Delta has been practiced for nearly 400 years, from 1620 when Vietnamese immigrants were allowed by Cambodian King Chey Chettha II to 2020. Today, the MRD is the major rice production area in Vietnam as it contributes more than 50% to the Vietnam’s national rice production yearly.

3.1 Rice Production in the Mekong River Delta Before 1975

In the 18^th century, Vietnamese migrants coming from the Northern and Central regions reached the Mekong Delta. This population of migrants reclaimed the land lying next to the rivers. They settled on the natural levees of rivers, especially the Mekong and Bassac rivers and cultivated the areas next to their houses in mostly rainfed shallow submergence-prone and rainfed medium-deep waterlogged ecosystems. However, during the second half of the 19^th century, only a small part of the Mekong Delta was cultivated. In 1862, French Army occupied the whole MRD (or Cochinchina) and invested in the digging of primary canals to allow drainage and transportation through the whole MRD and this made the land reclamation in most of the fallow areas became possible. In the 1930s, rice production in the MRD was estimated at around 2.5 million tons of paddy and MRD export around 1 million tons of white rice every year.

The Indochina war ended in 1954 and Vietnam was split into two parts: Southern Vietnam became the Republic of South Vietnam (RSV) and Northern Vietnam became the Democratic Republic of Vietnam (DRV). The government of RSV directed by Mr. Ngo Dinh Diem carried out land reforms. In 1967, the new government of General Nguyen Van Thieu also launched a new land reform known as the “land to the tiller”. In addition, first high-yielding rice varieties such as IR5 and IR8 were introduced to rice production in South Vietnam. From almost zero in 1968, HYV were grown on 890,000 ha in 1973.

3.2 Rice Production in the Mekong River Delta from 1975 to the Present

After 1975, many irrigated/drained systems have been constructed in the MRD. Fresh water could reach to some marginal land areas such as Ca Mau peninsula, Long Xuyen quadrangle, Dong Thap Muoi and reclaim them to arable areas. When water was supplied, rice cultivation in many areas shifted from 1 rice crop to 2 or even 3 rice crops per year. From 1975 to 1980, programs were launched to reclaim the unused land in the MRD for rice production and promote wide adoption of high yielding rice varieties.

After 1987, farmers in the MRD intensified rice cropping and planted up to three rice crops – namely monsoon crop (or Lua Mua), summer-autumn crop (or Lua He Thu) and winter-spring crop (or Lua Dong Xuan) – on the same pieces of land in a year. From 1996 to 1999, with further irrigation investment in the MRD, most of the formerly deep-water rice areas in the region have been converted to double cropping of short-duration and high-yielding varieties. In 2006 the rice land area in Mekong River Delta was 1,893,480 ha and in 2008, it was 1,873,000 ha. However, the rice land area in MRD was reduced to 1,873,750 ha in 2009.

Rice production in the MRD has seen phenomenal increase in the recent years. This increase is attributed to the planting of modern early maturing rice varieties, better crop management, and appropriate canal constructions. In 1995, the rice planted area in the MRD was about 3,190,600 ha or about 47.1% of the rice planted area in the whole Vietnam country. Both the rice planted area in the MRD and that in the whole Vietnam country increased steadily from 1995 to 2017. For the MRD, the rice planted area increased from 3,190,600 ha in 1995 to 4,185,300 ha in 2017. Similarly, for Vietnam, the rice planted area increased from 6,765,000 ha in 1995 to 7,705,200 ha in 2017. The rice planted area in the MRD, therefore, was about 47.1 % Vietnam’s rice planted area in 1995 and about 54.3% in 2017 (Table 1)

Table 1 Rice planted area in the MRD and that in whole Vietnam during the period from 1995 to 2017

In 1995, rice yield in the MRD was about 4.02 tons/ha and it increased steadily to 5.95 tons/ha in 2015 and then slightly reduced to 5.64 tons/ha in 2017. Similar trend was observed for Vietnam rice yield showing rice yield increased from about 3.69 tons/ha in 1995 to 5.76 tons/ha in 2015 and then reduced to 5.55 tons/ha in 2017. In general, rice yield in the MRD has been higher than the Vietnam’s national rice yield (Table 2).

Table 2 Rice yield in the MRD and that in whole Vietnam during the period from 1995 to 2017

Consequently, rice production in both the MRD and in the whole Vietnam increased steadily during the period from 1995 to 2017. The rice production of the MRD increased from 12,831,700 tons in 1995 to about 23,609,000 tons in 2017 and the rice production in the MRD during the period from 1995 to 2017 contributed yearly from 51.3% to 56.7% to Vietnam’s national rice production (Table 3)

Table 3 Rice production in the MRD and in whole Vietnam during the period from 1995 to 2017

3.3 Rice Cropping Season in the Mekong River Delta in the Recent Years

In the recent years, there are three rice seasons the MRD, namely the Winter-Spring or Dong Xuan (DX), the Summer-Autumn or He Thu (HT), and the Rainy Season or Mua (M). The Winter-Spring (DX) crop is planted in November/December and harvested in February/March; the Summer-Autumn (HT) crop is planted in May/June and harvested in August/September; and the Rainy Season (M) crop is planted in July/August and harvested in December/January (Table 4).

Table 4: Rice Seasons in the Mekong River Delta

4. EFFECT OF DROUGHT AND SALINITY ON RICE PRODUCTION IN THE MEKONG RIVER DELTA

Being a low-lying coastal region, the Mekong Delta is particularly susceptible to floods resulting from rises in sea level due to climate change. In recent years, saline water has started to encroach further inland from the ocean, to such a degree that farmers in some areas of the delta now speak of a “salty season”. Salinity level in the MRD normally begin to rise by the end of December (early dry season), reach a peak in March or April (late dry season), and fall afterward. Historically, the El Niño in 1997 and that in 2009 were strong. As a result, severe salinity intrusion occurred in the MRD in 1998 and 2010. In 2015 the second most severe El Niño worldwide occurred and in May 2016 the MRD was suffering from its worst drought in nearly a century with water level gone down to its lowest level since 1926.

However, all previous records have been broken during this 2020’s dry season. The water source in dry season 2019-2020 to MRD is much lower compare to the average water source of the 10 recent years. In March 2020, water flows from Mekong River is 20% lower than that in 2016. Accordingly, the intrusion of saline water into the MRD was deeper in March with peak of salinity appeared from 7 to 15 March.

Fig.1 Intrusion of salt water at 4g/l in large rivers in Mekong River Delta at middle of March 2020

5. TECHNICAL SOLUTIONS FOR RICE PRODUCTION IN THE MEKONG RIVER DELTA

Rising levels of salt water in rice fields are causing the overall yield to decrease in a substantial manner. In 2013, number of farmers in MRD experienced having entire fields destroyed by salt water that flooded into soils. In 2016, salinity intrusion increased in concentration and duration and vast tracks of land planted with rice in Ben Tre, Tra Vinh, Kien Giang were affected by salinity and drought at the reproductive stage. Rice yields in these provinces were reduced by 50-100%, or total loss.

At present, salinity is the second type of stress and is the most predominant hindrance to rice production, after drought, in the MRD. Rice is susceptible to salinity, specifically, at the early vegetative and later reproductive stages. Rice is more resistant to salinity at reproductive and grain filling than at germination and vegetative stages. The effect of salinity on rice includes inhibition of germination, difficulties in crop area establishment, leaf area development, decrease in dry matter production, delay in seed set and even sterility. The critical salinity level resulting in 50% yield loss in rice was estimated to be around 6.9 dS m⁻¹ or about 3.8 g/l for rice. In the short term, rice production in the MRD could adopt the following technical solutions for reducing the negative effects of drought and salinity on its productivity.

• Planting salt-tolerant rice varieties such as MTL664, MTL702, MTL461, MTL463, MTL504, MTL664, CL8, DH2, OM6976; OM1348, OM6677
• Applying Alternate Wetting and Drying (AWD) to save fresh water/irrigation water in rice cultivation in order to cope with the problem of intrusion of saltwater in dry season.
• Adjust planting date of Winter-Spring (DX) crop to minimize the effect of drought and salinity on this crop. In the 2019-2020 Winter-Spring (DX) rice crop, most farmers in the MRD sowed rice at one month earlier and they were able to have a bumper crop. In reality, drought and salinity in dry season is not surprisingly happen but it could be estimated at 6 months before it occurs.

In the long-term, the technical solutions for sustainable rice production in the MRD include:

• Moving from monoculture of 3 rice crops/year to production rice-based systems such as rice-other crops, rice-aquaculture, especially in areas along the seashore.
• Reducing a rice crop in upper stream area so that rice fields could absorb more flood water, alluvium and fish and shrimp in order to improve the water retention and fertility of rice soil for balancing out the salinity invasion in dry season.
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