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More for less in irrigated rice

By controlling irrigation, farmers can maintain rice yields using as much as 25 per cent less water (Raymond Panaligan/IRRI)
By controlling irrigation, farmers can maintain rice yields using as much as 25 per cent less water
Raymond Panaligan/IRRI

Received wisdom has long been that the more water applied the higher the yield of rice. But recent research and widespread farmer experience has proved that this is not so: yields comparable to continuously flooded rice can be achieved with significantly less water using a technique known as 'alternative wetting and drying' (AWD) or controlled irrigation. Many farmers who struggled to cover costs are now making a profit, and a bonus is that harmony has been restored to communities where disputes over access to water had soured neighbourly relations.

The initial work on AWD began almost a decade ago with scientists at IRRI who, with the Philippines Rice Research Institute (PhilRice), established that rice needed to be flooded to a depth of only 3-5 centimetres instead of the more usual ten cm. Moreover, flooding does not have to be continuous and the soil surface can be left to dry out before re-flooding. The cycle of alternate low-level flooding and drying is repeated throughout the growth of the crop, although flowering is a critical period when the soil must be flooded.

Monitoring water level is critical

As much as 25 per cent less water is needed for AWD and no other significant changes to crop management are required, except to ensure that their fields are accurately levelled, avoiding 'ponding' (pools) of water in low spots and excessive drying where the ground is high. Levelling also has the benefit that seed germination and growth are more even and weed growth is more consistently controlled, so yields are enhanced.

Using a 'level gauge' farmers are able to determine when re-flooding is required (IRRI)
Using a 'level gauge' farmers are able to determine when re-flooding is required
IRRI

In addition, a simple 'level gauge' has been devised to enable farmers to avoid over-drying of the soil and determine when re-flooding is required. A 40 cm length of 15 cm diameter plastic pipe or bamboo, with holes drilled in all sides, is sunk into the rice field until 20 cm protrudes above soil level. Farmers monitor the level of water inside the pipe; when the water level inside drops to some 15 cm below ground level the field is ready to be re-flooded. Initially, a 'level gauge' is placed in each field but after two or three seasons, farmers learn to judge the need for re-flooding by a crop's condition.

In the Philippines, AWD is now applied by many farmers in the Provinces of Tarlac, Nueva Ecija and Central Luzon, and the Philippines Water-Saving Work group (WSWG) has been given the task by the Department of Agriculture to facilitate adoption of AWD in all irrigated areas of the country. "We need to make AWD part of the farmers' culture," says Jovino De Dios, supervising science research specialist at PhilRice. While Victorino Erese, President of the Malaya Irrigators' Association (MIA), a group of 264 farmers, observes, "Before, people looked out only to themselves but with AWD, there's better unity among members." They both speak for the Philippines but their sentiments apply equally wherever irrigated rice is grown.

Outreach in Asia and the way ahead?

In Vietnam, 70 extensionists and farmers from different districts met in November 2008 to undergo a training-of-trainers workshop in An Giang, Vietnam's top rice producing province. Visiting farmers, who had adopted AWD, enthused to other participants about the savings they has achieved in fuel costs as well as the reduced lodging in direct-seeded rice.

In Bangladesh, a recent workshop, Adoption and Success of AWD Technology for Rice Production, included presentations by national scientists and extensionists, and assessments by three farmers of their experiences with AWD. The result was a unanimous recommendation to disseminate AWD nationwide, which was based on the benefits to farmers, saving of foreign exchange to buy fuel, and the reduction in the impacts on the environment.

Farmers in An Giang Province have been trained to pass on their knowledge of AWD (Bas Bouman, IRRI)
Farmers in An Giang Province have been trained to pass on their knowledge of AWD
Bas Bouman, IRRI

Despite its obvious benefits and advantages AWD is not always readily accepted by farmers. Experience shows that there may be vested interests in the status quo. An issue that needs to be resolved is where farmers pay a flat rate for water and not a proportion of pump costs: here only the pump owner benefits from reduced water usage whilst it is clear that the benefits of water saving are shared. Experience has also demonstrated that training of farmers and strong leadership of farmers' groups is required if there is to be a change in mind-set from self-interest in the past to future sharing for community benefit.

Nevertheless, with the prospect of global climate change, resulting in failed monsoons and other seasonal rains, and increasing competition for reduced water supplies from domestic and industrial users, there is a clear and urgent need to find new approaches to rice cultivation in order to sustain yields of this vital food crop on which billions depend. In the next 25 years, 15-20 million hectares of irrigated rice are likely to suffer some degree of water scarcity.

Bas Bouman, Head of IRRI's Crop and Environmental Sciences Division, has been intimately involved with AWD from its inception. He believes that farmers have no choice but to adopt water-saving technologies. "We often get asked how can you convince farmers to save water?" he says. "My reply is that we don't have to convince them to save what they don't have. These technologies are about helping farmers to get the best out of the limited water they have."

Date published: November 2009

 

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