Rice is the world's most popular grain crop. But it uses vast amounts of water to grow. A new and simple technology could reduce water wastage by up to 30% for rice growers. By Thin Lei Win.
Los Banos, Philippines. 7 June 2012. The plastic tube looks ordinary enough. It is 40 cm long and 15 cm wide and there are tiny holes on all sides. But according to scientists, this humble tube could save up to 30% of water used in producing rice - a staple food for more than half the world's population and arguably the single biggest user of water on the planet. "One tonne of rice needs two to three Olympic-sized swimming pools of water. So each time you save 30% on one tonne of rice, you get one Olympic-sized swimming pool of water," said Dr Bas Bouman, head of the crop and environmental sciences division at the Philippines-based International Rice Research Institute (IRRI). As the world's population grows, climate change causes the weather to become more erratic, and water for agriculture gets scarcer, it is becoming increasingly urgent to find ways to increase rice yields while combating resource depletion. Some estimates predict 15-20 million hectares (37-49 million acres) of irrigated rice may suffer water shortages by 2025. At the same, each hectare of land used to grow rice will have to provide for at least 43 people by 2050, compared to 27 people currently, according to IRRI, the biggest non-profit research centre on rice. If each of the 20 million hectares facing water shortages produces 5 tonnes of rice, "that's 100 million tonnes of rice and 200 to 300 million Olympic-sized swimming pools," Bouman told AlertNet. "And you can save one third of that. That's an awful lot of water."
Traditionally, farmers like to keep their rice fields topped with a layer of water until just before harvest. Under the alternative wet and drying method (AWD), the soil is allowed to dry out for a couple of days before irrigating it again, and this process is repeated until harvest. Not only does this save water, it can also improve yields, Bouman said. During the period the soil is not covered with water, rice roots start to grow faster and deeper because they're looking for nourishing moisture, he said, adding that better anchorage also help prevent rice stalks getting flattened by strong winds and rice grains consequently ending up in the mud. "We've found that in places like Vietnam, Bangladesh, and ... in the Philippines, they have 10% more yield under AWD," Bouman said. IRRI scientists are working on various technologies to ensure the rice gets the optimum water quantity. These include a sprinkler system - but perhaps the cheapest, easiest and most effective is the plastic tube. Bouman calls it "the hole in the ground" solution.
"We dig a hole about 30 cm deep, put one of these plastic pipes with holes in it so the water flows freely, then we just tell the farmers to look at the water," he said. This way, even when the water level falls below the surface, farmers can see the water level in the tube. They only irrigate again once it falls below a certain level, which they can measure using a ruler. "The rice roots are 20 cm deep so as long as your water is 5, 10, 15 cm below the surface, the roots can still easily tap it," Bouman said. "If you do that wisely, you can save 10 to 30 percent of water and you do not decrease your yield."
The plastic tube eliminates the need for complex tables or charts that would otherwise be needed to determine when farmers should irrigate, taking into account the soil type and terrain. Some farmers in Bangladesh can't afford the plastic tubes - they cost about US50 cents each – so they are using discarded plastic Coca-Cola bottles with the bottoms cut out. Other farmers in the Philippines choose bamboo tubes, Bouman said. Farmers in the Mekong delta in Vietnam are using the method with farmers in Myanmar soon to follow, added Bouman.
There's another possible benefit from the system: less methane. “Methane, a greenhouse gas 23 times more potent than carbon dioxide is emitted by rice fields under flooded conditions so it's logical to assume that under AWD with less flooding it emits less methane," said Bouman. So far, results from experiments at the IRRI farm have been encouraging. According to Bouman, methane emissions fell by 30 to 70% depending on a combination of water usage and management of rice stubble. However, methane emission varies with soil type so the data needs to be re-assessed for different soils and conditions, he added. But that pipe-with-holes solution looks like it can help increase yields and reduce greenhouses gases all in one go. Not bad!
Thin Lei Win is the Thomson Reuters Foundation's South Asia correspondent based in Bangkok.
Photos : Internet, Thin Lei Win