The science behind Alternate Wetting and Drying
We didn’t invent AWD. It is a well-studied method from the International Rice Research Institute. Here is what the evidence says, including where it is weak.
What AWD is
In Alternate Wetting and Drying (in Thai, เปียกสลับแห้ง), the paddy is allowed to dry for some days after the ponded water disappears, then re-flooded, repeatedly through the season, instead of being kept continuously flooded (IRRI, AWD fact sheet) (Bouman et al., 2007).
IRRI’s “safe AWD” protocol
| Element | IRRI guidance |
|---|---|
| Tool | A perforated field water tube, about 10 cm above and 20 cm below the soil surface, soil removed from inside |
| When to irrigate | When water in the tube drops to about 15 cm below the soil surface |
| How much | Re-flood to about 5 cm of standing water |
| When to start | About 1–2 weeks after transplanting |
| Flowering | Keep flooded from about one week before to one week after flowering |
| After flowering | Resume AWD during grain filling; drain before harvest |
Source: (IRRI, AWD fact sheet). Our NaLog platform uses the same −15 cm and +5 cm thresholds; see the sensor page.
What the evidence says
| Outcome | Typical finding | Sources |
|---|---|---|
| Water use | Safe AWD typically saves 15–30% of irrigation water; a global meta-analysis found −23% for mild AWD | (Bouman et al., 2007) (Richards & Sander, 2014) (Carrijo et al., 2017) |
| Yield | Mild AWD: no significant loss on average. Severe drying: yields fall by about 23% | (Carrijo et al., 2017) |
| Methane | About 50% lower on average than continuous flooding; IPCC 2019 default factors imply about 45% lower | (Jiang et al., 2019) (Zhao et al., 2024) (IPCC, 2019) |
| Nitrous oxide | Tends to increase; net greenhouse-gas benefit positive on average, but not at every site | (Jiang et al., 2019) (Chidthaisong et al., 2018) |
| Thai field evidence | Prachin Buri, 3 years: ~42% less water, ~49% less methane, no significant yield loss (one site, acid sulfate soil) | (Chidthaisong et al., 2018) |
| Farmer economics | AWD is most attractive where farmers pay for pumping | (Lampayan et al., 2015) (Richards & Sander, 2014) |
Limitations we take seriously
Arsenic and cadmium
Deeper soil drying can reduce grain arsenic (Linquist et al., 2015), but safe AWD at 15 cm may not(Carrijo et al., 2018), and cadmium can rise as soils dry (Carrijo et al., 2022). We make no food-safety claims.
Nitrous oxide
AWD trades some methane for more nitrous oxide. In the Thai study, the dry-season difference in net warming potential was not statistically significant (Chidthaisong et al., 2018).
Water access
AWD needs the ability to irrigate and drain; it is not recommended for purely rainfed rice(Richards & Sander, 2014). That limits where in Isan it applies.
Season and soil
Wet-season rain can stop fields drying (Sander et al., 2017), and shallow groundwater can keep the tube from ever reaching −15 cm, shrinking the savings (Bouman et al., 2007).
One more reason measurement matters: if a field never really drains, AWD’s methane benefit can be negligible(Richards & Sander, 2014). Logging how deep and how long a field actually dries is the gap oursensor and NaLog are designed to fill.
Sources
- IRRI Rice Knowledge Bank (Lampayan, Yadav, Humphreys). Saving Water with Alternate Wetting Drying (AWD). Fact sheet. www.knowledgebank.irri.org
- Bouman, B.A.M., Lampayan, R.M., Tuong, T.P. (2007). Water Management in Irrigated Rice: Coping with Water Scarcity. IRRI, Los Baños. books.irri.org
- Richards, M., Sander, B.O. (2014). Alternate wetting and drying in irrigated rice: Implementation guidance for policymakers and investors. CCAFS/IRRI Practice Brief. cgspace.cgiar.org
- Carrijo, D.R., Lundy, M.E., Linquist, B.A. (2017). Rice yields and water use under alternate wetting and drying irrigation: A meta-analysis. Field Crops Research 203, 173–180. doi:10.1016/j.fcr.2016.12.002
- Jiang, Y., et al. (2019). Water management to mitigate the global warming potential of rice systems: A global meta-analysis. Field Crops Research 234, 47–54. doi:10.1016/j.fcr.2019.02.010
- Zhao, C., Qiu, R., Zhang, T., Luo, Y., Agathokleous, E. (2024). Effects of AWD irrigation on methane and nitrous oxide emissions from rice fields: A meta-analysis. Global Change Biology 30, e17581. doi:10.1111/gcb.17581
- IPCC (2019). 2019 Refinement to the 2006 IPCC Guidelines for National Greenhouse Gas Inventories, Vol. 4, Ch. 5 Cropland. www.ipcc-nggip.iges.or.jp
- Chidthaisong, A., et al. (2018). Evaluating the effects of alternate wetting and drying (AWD) on methane and nitrous oxide emissions from a paddy field in Thailand. Soil Science and Plant Nutrition 64(1), 31–38. doi:10.1080/00380768.2017.1399044
- Linquist, B.A., et al. (2015). Reducing greenhouse gas emissions, water use, and grain arsenic levels in rice systems. Global Change Biology 21, 407–417. doi:10.1111/gcb.12701
- Carrijo, D.R., et al. (2018). Impacts of variable soil drying in alternate wetting and drying rice systems on yields, grain arsenic concentration and soil moisture dynamics. Field Crops Research 222, 101–110. doi:10.1016/j.fcr.2018.02.026
- Carrijo, D.R., LaHue, G.T., Parikh, S.J., Chaney, R.L., Linquist, B.A. (2022). Mitigating the accumulation of arsenic and cadmium in rice grain: A quantitative review of the role of water management. Science of the Total Environment 839, 156245. doi:10.1016/j.scitotenv.2022.156245
- Sander, B.O., Wassmann, R., Palao, L.K., Nelson, A. (2017). Climate-based suitability assessment for alternate wetting and drying water management in the Philippines. Carbon Management 8, 331–342. doi:10.1080/17583004.2017.1362945
- Lampayan, R.M., Rejesus, R.M., Singleton, G.R., Bouman, B.A.M. (2015). Adoption and economics of alternate wetting and drying water management for irrigated lowland rice. Field Crops Research 170, 95–108. doi:10.1016/j.fcr.2014.10.013