Science - January 26, 2010

Rice farmers in Senegal can save 40 percent of water

An alternative irrigation technique can enable rice farmers in Senegal to save twenty to forty percent of irrigation water, without lowering the rice output. Research done by Wageningen PhD student Michiel de Vries in field stations and at farms in Senegal seems to prove this, which will be published in an article in Field Crops Research this month.

Rice farmers in Senegal pump water daily from the Senegal River to keep their rice fields under 10 centimetres of water. This permanent inundation uses up a lot of water in this warm country. De Vries brought another method into bear, by irrigating once in three or four days. In this period, the water in the field drops from ten centimetres above ground level to ten centimetres below ground level. This alternate wetting and drying (AWD) method led to saving forty percent of irrigation water, while harvests amounted to 95 percent of the usual method.
The best results were achieved by combining both methods: the rice field was kept inundated during half the growing season, and in the other half, water for the field was rationed. By placing a simple pipe in the ground, rice farmers can measure the underground water level, and keep check on when they have to irrigate. Farmers can also use the AWD technique throughout the season, says de Vries. They would then save fifty percent of water, but would have an average of 20 percent less rice output. The irrigation costs are sometimes so high that this option is interesting for the rice farmers, he says.
Drinking water
To produce a kilo of rice, 1700 litres of water are needed in usual irrigation systems. De Vries can lower that to a thousand litres per kilo. Saving water is crucial in Senegal because the million-plus city Dakar also draws its drinking water from the Senegal River. Farmers also benefit since irrigation takes up an average of a quarter to a third of their production costs. Cost savings are important for these rice farmers because they have to compete with cheap imported rice from Asia in the market.
De Vries conducted his research at the rice institute WARDA in Senegal. 'In Asia, much research has been done into water-saving measures. My question is whether this is also possible in Sahel areas.' The agriculture information service in Senegal is very interested in his research and has financed a demonstration project in the meantime. Two Wageningen University students have also carried out field tests in farms.
This know-how is also applicable in other Sahel countries with rice cultivation, such as Burkino Faso, Mali and Niger, says De Vries. 'Major irrigation networks can also be found there. But it all depends on how these are set up. If farmers do not have to pay for water - for example when the government does the pumping for them - they wouldn't benefit from saving water and won't do so.'
De Vries has in the meantime found a job as breeder at a seed company in the Netherlands and works one day per week on his PhD. 'I am already more than halfway through.'