Sushil Pandey
International Rice Research Institute, Los Baños 4030, Philippines
Sudhir Yadav*
International Rice Research Institute, Los Baños 4030, Philippines
Jon Hellin
International Rice Research Institute, Los Baños 4030, Philippines
Jean Balié
International Rice Research Institute, Los Baños 4030, Philippines
Humnath Bhandari
International Rice Research Institute, Dhaka 1213, Bangladesh;
Arvind Kumar
International Rice Research Institute, Varanasi 221106, India
Manoranjan K. Mondal
International Rice Research Institute, Dhaka 1213, Bangladesh
AWD; Incentives; Social cohesion; Technology adoption; Water management
Crop-Soil-Water Management
Rice, Alternate wetting and drying
3. Alternate Wetting and Drying (AWD): Its Features, Adoption, and Effects Traditionally a rice field is continuously flooded. This practice evolved when water for irrigation was abundant and freely available or heavily subsidized. When water is physically or economically scarce, frequent irrigation becomes less feasible. Farmers are subsequently forced to practice intermittent irrigation. This may result in field-drying between irrigations and minimal to severe yield loss depending on the length of the irrigation interval and the crop growth stages. All such intermittent irrigation practices involve alternate wetting and drying (AWD), but the yield loss associated with “unintended” or “forced” AWD can be substantial.
In contrast, “safe-AWD” is a practice that maintains the yield level. It involves practicing intermittent irrigation guided by the observed soil moisture status. For example, a form of safe-AWD involves monitoring the depth of the perched water table, as indicated in perforated plastic tubes embedded in the soil, and irrigating when the perched water table falls below 15 cm from the soil surface. These guidelines were outputs from the Irrigated Rice Research Consortium (IRRC) under which many field experiments were conducted across Asia. The research showed a 15-cm fall in the water table is a safe threshold value to avoid any yield decline due to water stress while simultaneously significantly increasing the water productivity. Safe-AWD also includes ponded water at panicle initiation to flowering to avoid any stress at these critical growth stages. Different variants of safe-AWD allow for suitable adjustments in the timing and frequency of irrigation depending on the crop growth stage and farmers’ ability to control irrigation flow.
3.1. Adoption of Safe Alternate Wetting and Drying (AWD) in Bangladesh Safe-AWD was introduced to Bangladesh in 2004 and targeted at northwest Bangladesh—a major boro rice-growing area that suffers from water scarcity due to the rapid expansion of groundwater use for irrigation. Various agencies, including the Bangladesh Rice Research Institute (BRRI), Department of Agricultural Extension (DAE), and BADC, carried out farmer field evaluations and demonstrations trials together with farmer training from 2005 to 2009. Studies highlighted the potential irrigation water saving and economic benefits that could be realized with AWD.
There are no known studies that confirm a continued use (or expansion of coverage area) by those farmers who participated in the original piloting and field testing of AWD or by other non-participating farmers. It is also unclear how many farmers who participated invalidation trials decided to continue with the practice as no follow-up surveys were carried out. Activities to promote safe-AWD seem not to have expanded beyond the initial field testing and validation despite several national-level deliberations on the need to address water scarcity. A recent survey conducted in the northwest region of Bangladesh did not find any farmers who practiced AWD. This suggests constraints within and outside the irrigation sub-sector, stymying the diffusion of safe-AWD.
3.2. Effects of Safe Alternate Wetting and Drying Discerned from Field Testing and Validation Trials Indications of the effects of safe-AWD in Bangladesh can be discerned from field testing and validation trials. Most of these trials were conducted on farmers’ fields and involved comparing results from the safe-AWD treatments and farmers’ irrigation practices. Most of the studies indicate that the number of irrigations applied to boro rice under safe-AWD treatment is lower than farmers’ normal practices. Farmers used 14–21 irrigations under conventional practices compared to 10–16 irrigations under safe-AWD, a reduction of 27–35%. The reduction in the volume of water is likely to be less than the proportionate reduction in the number of irrigations as the amount of water applied to safe-AWD plots at each irrigation is generally more than water added to already-saturated or flooded plots. The observed savings in irrigation at the field level do not translate directly into savings at the system level due to return flows and recycling of drainage water. The drainage, runoff, and seepage losses from an individual field are often not losses at higher spatial scales. Runoff makes its way to other farmers’ fields or surface water bodies from where it may be reused in various ways, and drainage flows to the groundwater, from where it can be recycled by groundwater pumping (unless the groundwater quality is poor). Seepage flows to adjacent fields, surface drains, or groundwater. Thus, any irrigation water savings estimated through such field trials overestimate the actual water savings at a larger scale.
Water 2020, 12, 1510
Journal