In the context of increasingly complex climate change, environmental pollution has become a global issue; agricultural systems and farmers, especially in Southeast Asian countries with rice-based agriculture like Vietnam, are the most vulnerable subjects directly affected by extreme phenomena such as prolonged drought and saline intrusion, leading to a serious decline in the availability of clean water for irrigation. This poses a challenge that governments must face and seek multiple solutions to address.
After decades of research and experimentation with various methods, the Alternate Wetting and Drying irrigation technique (AWD) has proven to be remarkably effective. This is not a completely new technique globally, as it has been successfully applied by the International Rice Research Institute (IRRI) in countries such as Japan, China, Philippines, and Thailand.
In Vietnam, researchers have only recently begun experimenting with this method over the past decade, yet it has already shown promising results. With the goal of addressing challenges hindering the full utilization of AWD and turning it into a significant contributor to the country's agricultural sector, BSB Nano Technology Company representing Vietnam, Net Zero Carbon from Thailand, and Spiro Carbon, a company headquartered in the United States, have jointly launched a cooperation program known as BNS (BSB Nanotechnology – Net Zero Carbon – Spiro Carbon). The combined expertise of these three companies in various areas holds the potential for a sustainable agriculture sector that not only enhances productivity but also fosters environmental conservation.
1. ADW’s overview
1.1 Technique
According to research by IRRI, rice plants only need to be submerged during the initial stages of rooting and tillering, as well as requiring water to be pumped into the fields to a maximum depth of 5cm (Van Der Hoek et al., 2001). Specifically, different adjustments to the water level are needed at various stages.
• First week after sowing
During the initial stage after sowing seeds, the water level in the field is maintained at a high level of about 1 cm. It is crucial to keep the water at this level throughout the initial development stage of the rice plants until the second fertilization, approximately 20-25 days after sowing. This water level not only provides the necessary conditions for the growth of rice plants but also prevents the germination of harmful weed seeds.
• Stage from 25-40 days
During the tillering stage, the rice plants grow vigorously and require less water. The water level in the field needs to be maintained at a depth of 15 cm below the soil surface to encourage deep root growth of the rice plants and prevent competition from weeds. Adjusting water in the field in this manner is referred to as "alternate wetting and drying" irrigation. The equipment needed is a perforated pipe, with internal markings every 5 cm for monitoring purposes.
Fig.1. Water Level Measuring Device Model (Source: CGIAR)
• Stage of rice growth from 40-45 days
This is the time for the third fertilization (top-dressing). Before fertilizing, the water level in the field needs to be maintained at a range of 1-3 cm to prevent fertilizer damage or evaporation.
• Stage of rice growth from 60-70 days
During the period from day 60 to day 70 after sowing, the rice plants are in the flowering stage and require a water level of 3-5 cm for about 10 days to ensure smooth pollination.
• Stage after 70 days until harvest
Finally, from day 70 until harvest, the rice plants only require water level from ground level to 15 cm below ground level. To facilitate harvesting, it is advisable to reduce the water level 10 days before harvesting to ensure the field is dry.
Fig. 2. Water management for continuous flooding and alternate wetting and drying.
(Leon & Izumi, 2022)
1.2 Advantages
After years of research and data collection, IRRI has established the clear effectiveness of the Alternate Wetting and Drying (AWD) technique in three aspects:
Water saving: At the core of reducing the duration of flooded conditions during the rice growing season, AWD can help reduce irrigation water usage by up to 40%.
Greenhouse gas reduction: AWD is believed to reduce methane gas (CH4) emissions from rice cultivation by 50%. The process of draining water creates a dry environment on the rice field surface, disrupting the anaerobic conditions for methane-producing bacteria (Yang et al., 2020).
Increased agricultural profitability: By reducing production costs (water, labor, time) while maintaining productivity and quality of rice crops, AWD brings better economic value to farmers (Arai et al., 2021).
2. Applications of AWD in Vietnam
2.1 The current situation
The Mekong Delta (MD) is the largest rice bowl in Vietnam, consisting of various agricultural ecological sub-regions including alluvial soil, saline-affected soil, flood-prone soil, and alkali-affected soil, leading to differences in greenhouse gas emissions between these regions. Generally, methane (CH4) emissions in the MD are estimated at 1.92 kg CH4/ha/day, while the CH4 emission factor in Southeast Asia is 1.22 kg CH4/ha/day, similar to the global default emission factor of 1.19 kg CH4/ha/day (Yona et al., 2020). This indicates that the average CH4 emission level in the MD exceeds the global average threshold (nguyen cong et al., 2022).
Moreover, facing the impacts of climate change and seawater intrusion, in 2017, the Vietnamese government through Resolution 120, outlined plans to utilize sustainable farming methods, requiring farmers in the delta region to find ways to reduce water consumption for irrigation. These factors have prompted the experimentation and research on the application of AWD in Vietnam.
2.2 Variant of AWD in Vietnam
The application of Alternate Wetting and Drying in Vietnam may face some drawbacks, such as potential increases in N2O emissions and nutrient loss in soil. Additionally, its implementation may inconvenience farmers. To address these challenges, a simpler version of AWD known as AWD Farmer (AWDF) has been developed. In AWDF, farmers rely on their own experience to determine the timing of water application without adhering strictly to the 15cm water level drop required in standard AWD.
AWDF is commonly practiced in An Giang province, where an extensive system of dikes facilitates its implementation. Studies have shown that AWDF fields experience a significant reduction (by 35%) in total CH4 emissions per season compared to traditional continuous flooding. However, there is no difference in N2O emissions between AWDF and continuous flooding.
These findings suggest that AWDF, if fully adopted, can effectively mitigate CH4 emissions in rice fields without compromising soil nitrogen nutrient levels. Moreover, Vietnamese farmers typically employ AWDF mainly during the rainy season when water reserves are plentiful. In seasons with low rainfall, continuous flooding is preferred as a precaution against drought.
2.3 The potential of AWD in Vietnam
Research data indicates that in the Mekong Delta, rice productivity, harvest index, and grain filling ratio in AWD - managed fields are higher compared to fields managed with continuous flooding, by 8.9%, 4.4%, and 3.5%, respectively. Furthermore, the nitrogen content in rice grains is lower, and water usage is also reduced by 43% when AWD is applied (Arai et al., 2021).
Cost-benefit analysis of AWD reveals that it contributes to increasing the net income of farmers mainly by reducing production costs. The net additional income for farmers is approximately 8,540 billion VND (equivalent to 371.36 million USD) per year compared to conventional rice cultivation (Mai et al., 2019).
2.4 The hurdles
Two major obstacles to expanding the AWD model in Vietnam are substandard irrigation system quality and low economic efficiency.
The main reason is that Vietnam's agriculture system has developed towards small-scale family farming, with the average cultivation area per household being only about 0.13 hectares, a very small figure. The value of agricultural products harvested from this area is not sufficient to offset the cost of installing modern irrigation systems to serve AWD. Additionally, the access to information and awareness of farmers regarding agricultural modernization and environmental protection varies greatly, leading to heterogeneous farming methods being applied within the same cultivation area. This is unfavorable for the effectiveness of AWD. If only a small area is dried out while the surrounding areas continue with full-time flooding, rodents and other pests tend to aggressively attack the drier land, further reducing the effectiveness of the AWD model (Gupta et al., 2023).
2.5 The development direction
2.5.1 IoT
A device for measuring water levels in the field using IoT (Internet of Things) technology, powered by solar energy, has been successfully researched and deployed in Vietnam. This technology allows users to manage the water level in the field through management software set up on their mobile devices connected to a satellite-connected sensor placed in the field. Through this, users can control and start the pump from their mobile phones to let water into the field when the water level is below the threshold of AWD.
As a result, combining AWD with IoT brings remarkable efficiency, helping farmers save additionally 13% – 20% of water compared to manual AWD. Besides, AWD with IoT helps them save energy and time. In the final stage, IoT application generated higher productivity than manual AWD with an increase of more than 11% in Can Tho and nearly 5% in Tra Vinh and An Giang (Gupta et al., 2023).
2.5.2 Using bio-based fertilizers and plant protection products
During the transitional stages between flooding and drying, rice plants need time to adapt to the changes, which is a vulnerable period for attacks by pests. Support from plant protection products and fertilizers is crucial to ensure that the rice yield is not compromised. However, farmers also need to carefully choose products with a biological origin that are not harmful to the environment and humans to fully realize the sustainable agricultural value of the AWD method.
2.6 The BNS cooperation program
BNS (BSB Nanotechnology – Net Zero Carbon – Spiro Carbon) offers a comprehensive solution for modernizing agriculture, aiming towards sustainable development. This collaboration will leverage Spiro Carbon's artificial intelligence technology, headquartered in the United States, specializing in analyzing data from various sources, including satellite images, to monitor and evaluate the reduction of greenhouse gas emissions in rice cultivation. Through this project, participating farmers can generate additional income by selling carbon offsets to individuals interested in environmental protection. Additionally, the process of extracting nano silica from rice bran by BSB Nanotechnology, such as ECO OK, will provide organic solutions for crop management, including fungal, pest, virus, and harmful bacteria control, thereby increasing productivity, reducing costs, and aligning with sustainable farming practices.
The implementation plan of BNS is no longer just a concept on paper but has been put into practical research in Thailand and Vietnam. In the years 2023-2024, Dak Lak, Binh Phuoc, Dong Thap, Hau Giang, and Kien Giang provinces are pioneering in adopting the BNS solution package, with the model expanding across the Mekong Delta starting from the next crop season.
Bibliography
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