In Vietnam, the development of intensified crop production systems and high-yielding modern varieties that are aimed at addressing problems in food security increased the amount of crop residues (rice straw, rice husk, coffee husk, and other agricultural by-products) being left in the field after harvest. Vietnam, considering that it is an agriculture-dominant country, produces annually almost 100 million tons of crop residues and other agricultural by-products. Agro-input pollution has increased dramatically in Vietnam over the last two decades together with the expansion and intensification of crop farming. Accompanying this development has been wastes from the irrational application of intensive farming methods and the abuse of chemicals used in cultivation, remarkably affecting rural environments in particular and the global environmental in general. Livestock production is not only growing but also industrializing and spatially concentrating often in troublesome proximity to densely populated areas even while remaining smallholder-dominated. Wastes from livestock activities include solid wastes such as manure and organic materials in the slaughterhouse; wastewater such as urine, cage wash water, wastewater from the bathing of animals and from maintaining sanitation in slaughterhouses; air pollutants such as H2S and CH4; and odors. The estimated 84 million tons of livestock wastes generated each year are vectors of nutrients, pathogens, and volatile compounds that compromise water and air quality and damage soils. Recently, agricultural waste management for ecological agriculture and sustainable development has become an issue of concern for the Vietnamese government. The government and other functional organizations are paying greater attention to means of recycling agricultural wastes and residuals. This paper aimed at providing an overview of waste generation from cultivation, livestock activities and evaluates potential benefits of agricultural wastes and residuals in Vietnam. In addition, it also identifies options in recycling agricultural wastes and residuals for contributing to clean, safe, and sustainable agriculture.
Keywords: Agricultural wastes, residuals, solid waste, cultivation, livestock, Vietnam
The agricultural sector is one of the key contributors to the Vietnamese economy and has developed rapidly in the recent two decades. It shared approximately 15% of total Vietnamese gross domestic product (GDP) between 2010 and 2019. The country has become one of world's largest rice exporters during the last 10 years and is also now a key partner of many developed countries such as the USA, EU, Japan, Australia, Korea, China… in terms of the export of other agricultural commodities. However, accompanying this development are wastes from the irrational application of intensive farming methods and the abuse of chemicals used in cultivation, remarkably affecting rural environments in particular and the global environmental in general. Wastes generated from agricultural sector such as plant residues after harvesting and cattle manure include hydrocarbons, proteins, lipids, and some other organic compounds. Recently, agricultural wastes and residual management for ecological agriculture and sustainable development has become an issue of concern for the government. This paper aims to provide a broad national overview of agricultural wastes and residuals generation from cultivation, livestock sector in Vietnam. It also outlines some potential options for effective recycling of agricultural wastes and residuals.
MANAGEMENT OF WASTES AND RESIDUES FROM CROP OUTPUT
Total residues and agricultural by-products from staple crop and industrial crop were estimated at 95-98 million tons per year. According to survey data from the Institute of Agricultural Environment (IAE) of Vietnam, by 2019, these generated wastes included 52 million tons of straw and husk, 10.9 million tons of maize residues, 10.3 million tons of cassava residues and by-products, 16.9 million tons of sugarcane residues and by-products, 4.5 million tons of coﬀee residues and by-products.
Rice is the most important staple food in Vietnam, so the government always gives its highest priority to maintain the rice area to ensure food security for the country. In 2019, around 7.5 million ha of land were devoted to harvesting rice, produced annually and generating 44 million tons of rice straw. The Mekong Delta has played a central role in sustaining Vietnam’s high level of rice production: Although the entire delta (3.9 million ha) only accounts for approximately 10% of the country’s total area, half of the national rice production and approximately 90% of annual rice exports originate from it. With favorable conditions for rice production, the Mekong Delta annually yields approximately 24 million tons of rough rice and an estimated 24 million tons of straw (dry weight of the total aboveground biomass) and 4.9 million tons of rice husk. The rate of rice straw and husk generation in Mekong River Delta accounts for 56% of the total amount in the country.
Maize is the second most important food crop with regards to harvested area, production, and rural livelihoods, especially in mountainous areas. It is also an important source of feed for livestock and aquaculture. This is an important crop in hunger elimination and poverty reduction programs. The planted area and production of maize in 2018 were about 1.09 million ha and 5.13 million tons, respectively. The regions covering the North West Mountainous and Central Highlands have the largest maize area and production, which account for nearly 60 % of total maize grown area and production of the nation. These two regions annually produce approximately 6 million tons of residues (aboveground biomass) and corn-cobs, accounting for 62% of the total amount in the country.
The country's growing area and production of cassava is estimated at 530,000 has and 10.4 million tons in 2018. Cassava was planted mostly in the North Central Coast, Central Highland and South-east regions. By-products from cassava are mainly tops, fresh leaves, stubble and pulp, cortex after processing. It is estimated that in 2018, the quantity of cassava residues and by-products were about 7.9 million tons.
Coffee is the main perennial industrial crop and main source of rural income in the Central Highlands. At present, the coffee area is reported to be over 688,000 ha, 90% of which is located in the Gia Lai, Dak Lak, Dak Nong, and Lam Dong Provinces, and produce 1.62 million tons of coffee grains. The region annually produces approximately 4.4 million tons of coﬀee residues and by-products.
According to survey data from Low Carbon Agricultural Support Project (LCASP, 2015) Vietnamese farmers have several kinds of rice residue management in order to manage rice residue in the field: (1) burn residue in the field, (2) incorporate it into the field, and (3) remove it from the field, either for feeding cattle herds or mulch for succeeding crops. Rice residues removed from the field were also used as cooking fuel, as a substrate for composting, or for mushroom cultivation. Individual household conditions will determine the disposal method. The survey data also showed that more than 50% of the farmers burned or/and incorporated rice straw into after harvesting. The open-field burning of rice straw is still a major problem in intensive rice-based cropping systems in Vietnam. Rice straw is generally considered a form of waste, and most has usually been burned after rice harvest. Burning of rice residues has been a common practice to eliminate “wastes” after harvesting because it is a quick and cheap way, not only to manage rice residues while preventing pests and diseases, but also to reduce the fallow time between two rice crops. It is also a rapid way to address time and labor constraints as labor is in short supply and expensive if the straw is to be dealt with any other way than burning.
Based on survey data and estimation from the Institute of Agricultural Environment (2019):
- Rice straw and rice husks are mainly burned or incorporated into the field by 24-30%, used as a substrate for composting by 3.4-16.4%, used as animal feed by 2.1%; barn padding by 2.1-8.9%; used as cooking fuel by 2.6-20.3%, the rest (29.3-51.4%) is sold for other production materials. Some reports suggest that alternative uses of straw increased after 2015, helped by increases in the selling price of rice straw and the availability of equipment to collect and roll it.
- Maize: Corn stubble and leaves are often burned right in the field after harvest (accounting for 35.4%), used for animal feeds (34.4%), dried for cooking fuel (17.6%) and used as mulch for succeeding crops (4.1%). maize by-products are sometimes used for producing animal feeds (fermented and fresh feeds)
- Cassava: Local cassava stubble are used as material seedling for the next season (40-51.9%). Pulp and cortex after processing were mainly used for composting (76.2%).
- Coffee: 90% of coffee leaves are reused, the remaining 10% burned in the field; 100% coffee outer skin/cover is processed and reused. Only 10% of coffee grounds are reused as fertilizer, the substrate for ornamental plants; the rest is discharged into the environment as wastes. Coffee husks are sometimes used for producing black coal for domestic use and in industries.
MANAGEMENT OF WASTES FROM FARMING INPUTS
Solid wastes generated from agricultural production activities are one of the big emerging problems in the rural areas of Vietnam. Toxic solid wastes from farming activities include residues of pesticides, fertilizers, and packaging materials (that is, bottles and bags). The consumption of pesticides in Vietnam has increased dramatically in the past decades together with the intensification of the agricultural sector. According to preliminary statistics, around 11,000 tons of pesticide packaging materials and 240,000 tons of fertilizer packaging materials were generated nationwide but only about 40% of the pesticide packages are collected, in which about 17.7% are processed properly by burning method; the remaining 42.3% is disposed of as ordinary wastes (buried or incinerated at low temperature). On average, the volume of packaging materials accounted for about 10-15% of the total volume of pesticides/fertilizers. These wastes increased together with the increased use of pesticides and fertilizers in recent years. The problem is getting worse because those wastes were not handled and treated properly. The present most common ways are burning and burying them. Smoke released from burning causes air pollution and affects public health. Residues of pesticides and fertilizers from packaging bags and bottles could follow rainwater and irrigated water going to rivers and canals, which will then cause soil and water pollution killing fisheries and other aquatic animals.
In rice production, on average, 1 ha of rice farming produce 12.8 kg of solid wastes, including plastic (75.8 %), glass and metal (21.9 %), nylon (1.7 %), and paper (0.6 %) (Bui, Vo, and Nguyen 2013). Packaging materials of fertilizers and pesticides are major sources contributing to this waste. Most farmers did not practice safe handling and storage of pesticides and fertilizers, and wastes generated from packaging materials at present are poorly managed. More than 70 % of farmers in the Mekong Delta, after using pesticides, dumped the bottles, bags, and so on into canals or in the rice fields. Only 17 % farmers were reported to collect the wastes and treat them by burying or selling them for recycling. In short, rice farming activities, particularly in the MKD, generate a huge amount of solid wastes, particularly from packaging materials of pesticides and fertilizers. This is one of the challenges faced by the rural environment, including increasing water and soil pollution. This problem needs to be addressed urgently. Rice producers themselves have to find suitable waste management solutions to reduce and stop it. At present, the government’s monitoring and enforcement on agricultural waste handling and treatment is inadequate and not effective (MONRE 2014) as local authorities only encourage awareness of farmers on protecting the environment rather than making it a compulsory requirement. In addition, waste treatment technologies and facilities in rural areas are not available, so farmers have to do it in their own ways.
MANAGEMENT OF WASTES FROM LIVESTOCK
Current situation of waste generation from livestock
The livestock sector in Vietnam plays an important role in agriculture. It accounts for 35 % of agricultural gross value added. Livestock is one of the fastest growing sub-sectors of agricultural production in Vietnam. Semi-industrial and industrial livestock production accounted for 64.2 % of the sub-sector’s total output; smallholder and small-scale production accounted for the remainder. Intensification has been the sector’s response to rising demand, especially in pig and poultry production, and this pattern has given rise to environmental problems. Livestock population has been growing while the number of households raising animals has declined. Intensification of livestock farming from big farms often produce wastes much more than their capacity to recycle them for use as fertilizers and biogas.
The shift from traditional extensive livestock farming to intensive animal production is generating growing volumes of animal wastes. As of 2019, Vietnam’s livestock sector generated an estimated 86.92 million tons, higher than 2.62 million tons as compared to 2018.
The total amount of animal solid wastes generated in the country is around 87 million tons in 2019. Pigs account for 20 %, poultry 39 %, cows 23 %t, and buffalos 14 %. The cattle (cow, buffalo, pig) farming generated the 65% of solid wastes from livestock. In terms of geographical distribution, the region that generates the most livestock wastes is the Red River Delta, followed by the South East, and the Mekong River Delta. Pig farming was concentrated mainly in lowlands and populated areas and causes the greatest pollution compared to other animal farming species. Pig manure is also in slurry form and not easily collected. About 80 % of the manure is generated by smallholder farms, and the remainder comes from commercial farms. Smallholder farms account for the largest share of buffalo farms (98.8 %), but also a high percentage of cattle (89.4 %), pig (75.0 %), and poultry farms (71.8 %).
In 2019, around 68% of the total number of livestock farms have applied measures to treat animal wastes (30.2% treated by biogas systems, 25.6% separated solid waste to sell out, 6.4% used bio-mat bedding, 1.9% used for composting and 3.9% applied other treatment methods), and 32% did not apply any treatment before discharging into the environment. The rate of smallholder farms that did not apply animal waste treatment is about 47% (IAE, 2019).
From a species perspective, pig farms discharge the highest percentage of manure directly (42.4 %). The next highest percentages are found in buffalo (41.1 %), cattle (32.6 %), and poultry farms (28.8 %). In every region, smallholder farms discharge a larger volume of manure directly to the environment than intensive farms. In the Red River Delta, the region with the largest pig population in Vietnam, it was reported that 82% of manure from intensive farming systems was treated while only 39 % of manure from extensive farming systems was treated (DLP-MARD, 2015a). There are large variations in the degree of animal waste pollution among regions and even within provinces, with these partly reflecting the differences in livestock density in different locations.
Animal wastes management practices:
Animal wastes are currently being managed in a variety of ways that include composting, the use of biogas digesters, and the direct use of raw manure as fertilizer. In composting, solid wastes are collected and composted to produce organic fertilizers whereas the liquid fraction washed off the floor and discharged to the surrounding environment or fishponds. In biogas, wastes are collected and treated in biogas tanks; gasses produced are used for cooking and biogas effluents are used as fertilizers or discharged into fishponds for farming fish. In some places, raw manure (that is, chicken manure) is sold and applied directly to crops as organic fertilizers. Waste management practices are diverse, depending on specific farm conditions, such as types of animals, housing systems, locations, and farm sizes.
In pig farming
Vietnam’s land area for waste disposal in pig farms is often very small, especially in the northern commercial pig farms. About 30 % of pig farms are reported to practice separate collection of solid and liquid wastes, and 60 % of farms treat wastes in the form of a mixture. The use of biogas digesters to treat wastes is fairly widespread. About 53 % of pig farms in the south, 60 % in the north, and 42 % in the central regions were reported to use biogas digesters for waste treatment (Vu Chi Cuong, 2014). In many smallholder farms, solid wastes are collected and composted with rice straw and used as fertilizer for crops. Where biogas digesters are used, it is quite common that liquids and solids are mixed and put into digesters. About 35.5 % of pig farms reported storing their pig wastes without treatment and about 40 % of pig wastes were discharged directly into the environment without treatment (DLP-MARD 2015a).
A few experiments involving the treatment of biogas digester wastewater with secondary effective microorganisms (EM) have yielded good results in experimental conditions. The use of secondary EM in the treatment of wastewater from biogas digesters in Vietnam has reportedly brought the concentration of chemical oxygen demand (COD), five-day biochemical oxygen demand (BOD5), nitrite (NO2-), nitrate (NO3-), phosphorus (P) total, and coliforms (after 15 days of treatment) to acceptable levels. Experiments using water hyacinth to treat wastewater after biogas (that is, hyacinth per water surface area of 75 %) showed similar results. Despite the promising results, these practices still are not widely adopted by farmers because they require a relatively large treatment area and smallest farmers in Vietnam do not have adequate space (Nguyen Hong Tin, 2017).
In poultry farming
Poultry manure tends to be the farmers’ preferred type of organic fertilizer because it contains high protein content and other essential nutrients for plants. In addition, it has a high content of dried matter and it is more easily collected and handled and less costly to transport compared to other animal wastes. It is quite common for farmers to apply litter directly to crops (or to temporarily store it for this purpose) after removing it from poultry houses. In commercial farms, chicken manure is mostly sold to collectors directly without treatment. Farmers and fertilizer producers may come and buy solid manure directly at chicken farms or through middlemen. Chicken manure is a preferred source of organic fertilizer for coffee, pepper, and fruit trees. In 2014, approximately 23.4 million tons of poultry manure was reportedly generated from poultry farms, of which about 75 % was directly used as fertilizer.
In dairy cattle
In dairy farming, approaches to waste treatment vary greatly among locations. These include traditional approaches that involve digging a hole underground to store manure and using biogas digesters to treat wastes and produce gas for household uses. Some farms sell wastes to local collectors for composting. An environmental study on dairy farms in Ba Vi showed that about 72.2 % of dairy-raising households used biogas digesters for waste treatment and the remaining households (27.8 %) used composting. However, in dairy farms near big and mid-sized cities like Hanoi, HCMC, the amount of manure exceeded the land’s nutrient load capacity (Le Van Thuc, 2012; Duteurtre et al. 2015). Enforcement of environmental regulations was weak to protect surface and groundwater from contamination by dairy cow manure. In Vietnam’s biggest and most modern commercial dairy company, TH True Milk Company, located in Nghe An, bio-mat bedding is used to collect the solid part of manure in the barn. Because collected litter is a good source of organic fertilizer, the farm sells it to rubber and coffee plantations. The liquid wastes are treated in an industrial station (treatment capacity is 60 m3 per hour, which is equal to 1,500 m3 per day), in which it will undergo three stages of treatment sedimentation, strainer (at this stage, the water is still yellow), and treatment with chlorine (bleach water). After treatment, the wastewater is discharged into a nearby lake (Duteurtre et al. 2015).
In beef cattle and buffalo farming:
Most cattle and buffalo continue to be raised in extensive, low-intensity systems, and the wastes these generate have yet to cause major environmental problems at this stage; however, this situation is changing. Most manure is collected or recycled back to grazing lands. However, with the emerging of some large-scale commercial farms, there could be environmental pollution in the future. Smallholder, small-scale, and large-scale commercial cattle farms with separate manure treatment areas were reported to be around 48.3 %, 55.1 %, and 51.7 %t, respectively. Those using composting method for manure treatment were reported to be around 38.7 %, 34.4 %, and 24.1 %, respectively. A large proportion of liquid wastes (76.5 %of smallholders, 65.5 percent of small-scale, and 75.8 % of large-scale cattle farms) were discharged directly to the environment. The percentage of buffalo-raising households in the NMM, North Central Coast, and South Central Coast regions having compost piles were reported to be around 31.1 %. Only 0.5 % of surveyed households used biogas digesters, and they were mostly located in the NMM region (Đinh 2009).
Cattle manure is characterized by high fiber content, a lower concentration of protein, and a less offensive odor. Cattle manure is widely used as a source of organic fertilizer for various crops such as elephant grass, bonsai, coffee, pepper, and fruit trees. It is common for the manure to be dried under the sun for about three to four days and then mixed with lime, rice straw, rice husk ash, or coconut fiber. Liquid cattle manure can be used to make biogas as well as fertilizer for gardens.
The agricultural sector plays an important role in Vietnam’s economy. Food demand has also increased dramatically as population and incomes have increased, and food consumption patterns have shifted. The two past decades have seen very high rate of growth in the agricultural sector. Together with the trend of agricultural intensification that are aimed at responding to surge in demand, the amount of agriculture wastes and residues from crop production and livestock increased rapidly. Vietnam produces annually almost 100 million tons of crop residues/agricultural by-products and generated 84 million tons of livestock waste each year. In recent years, agricultural waste management for ecological agriculture and sustainable development has become an issue of concern for the Vietnamese government. The government and functional organizations have given some efforts to promote means of recycling agricultural wastes and residuals but there is a gap between potential of agricultural wastes and residual recycling and on-the ground performance realities due to the sector’s low capacity for waste handling, treatment, and management.
Bui, Nga Thi, Hung Xuan Vo, and Nhan Phan Nguyen. 2013. “Present Status and Solutions for Solid Wastes Managements in Rice Cultivations in Hau Giang Province.” Can Tho University 29: 83–88 (in Vietnamese). https://sj.ctu.edu.vn/ql/docgia/tacgia-2310/ baibao-10326.html. Nguyễn, Bộ Văn. 2013. Nâng cao hiệu quả sử dụng phân bón ở Việt Nam. Kỷ yếu hội thảo quốc gia về nâng cao hiệu quả quản lý và sử dụng phân bón tại Việt Nam. Nhà xuất bản nông nghiệp
DLP-MARD (Department of Livestock Production, Ministry of Agriculture and Rural Development). 2015a. Overview of Vietnam Livestock Sector Development Strategy and Restructuring Plan. The International Workshop “Vietnam Livestock Sector in Economic Integration: Experience Sharing Future Orientation.” Hanoi, October 27.
DLP-MARD (Department of Livestock Production, Ministry of Agriculture and Rural Development). 2015b. Xử lý chất thải trong chăn nuôi, Hội thảo xử lý chất thải trong chăn nuôi, thực trang và giải pháp, tháng 10, 2015, Hà Nội.
Duteurtre, G., J.-D. Cesaro, H. M. Nguyen, K. D. Pham, and L. N. Nguyen. 2015. The TH Milk Company (Vietnam): Is Such a LargeScale Investment Sustainable. REVALTER Project working paper based on a visit conducted in Nghia Dan District (Nghe An Province). CIRAD and Rural Development Center, Hanoi, July 2. https://agritrop.cirad.fr/579403/1/Report%20visit%20to%20 TH%20mega-farm%20VF2.pdf
Đinh Xuân Tùng. 2009. Báo cáo điều tra quy mô, năng xuất và hiệu quả chăn nuôi lợn và trâu bò. Cục Chăn Nuôi, Bộ Nông nghiệp và PTNT.
GSO (General Statistical Office). 2019. Statistical Yearbook of Vietnam. Statistical Publishing House, Hanoi, Vietnam (online database). http://gso.gov.vn/Default_en.aspx?tabid=766.
LCASP (Low Carbon Agricultural Support Project). 2015. Evaluation of the demand for vocational training on agricultural waste use and low carbon agricultural production - LCASP project. The consultant report, submitted on 5/2015 by Le Thi Nhung.
Lê, Văn Thực. 2012. Kết quả bước đầu nghiên cứu về môi trường trong chăn nuôi bò sữa quy mô nông hộ tại Ba Vì. Báo cáo khoa học, Viện Chăn Nuôi, Bộ NN-PTNT.
Nguyen Hong Tin. 2017. An overview of agricultural pollution in Vietnam: the crops sector. The report submitted to The World Bank’s Agriculture and Environment and Natural Resources Global Practices. Edited by Emilie Cassou and Binh Thang Cao. World Bank, Washington, DC.
Vũ Chí Cương. 2014. Nghiên cứu ứng dụng các giải pháp khoa học và công nghệ trong chăn nuôi lợn công nghiệp nhằm giảm thiểu ô nhiễm môi trường. Báo cáo tổng kết đề tài cấp nhà nước. Viện Chăn Nuôi, Bộ NN-PTNT.