Science - March 2, 2006

Rice growing in Vietnam bad for soil

Farmers in the Dong Anh district of Vietnam grow vegetables in combination with wet rice. Wageningen researchers and Vietnamese colleagues examined the crop growing system and concluded that wet rice growing is disastrous for soil quality. The farmers would do better to concentrate on vegetables and buy their rice.

Dr Arij Everaarts of PPO conducted the research together with Siebe van Wijk of LEI and researchers at the Agricultural University in Hanoi. In the Dong Anh district near Hanoi they visited farmers that specialise in growing vegetables such as broccoli, cabbage, tomatoes, beans and peppers. Once a year these farmers inundate their land with water to grow wet rice.

Alternating between dry cultivation of vegetables and wet rice cultivation is very bad for soil quality, according to the researchers. The muddy soil remains very acid once it has dried out and its structure is not good for vegetable growing. Everaarts: ‘We see this negative effect of wet rice cultivation on the soil not only in Dong Anh, but also in other parts of Vietnam and other Southeast Asian countries, like Indonesia and the Philippines.’ The researchers’ conclusion is that farmers in Dong Anh would do better to stop growing rice. This would enable them to be more successful in improving soil fertility through applying organic manure and crop remains. When vegetable fields are submerged under water each year for wet rice cultivation the organic matter and minerals are washed away.

In Vietnam, however, rice is regarded as a basic need. Even if the vegetable harvest fails, at least there will still be a sack of rice to live off, is one of the main reasons for growing rice. The researchers are aware of this, but still believe that in the long term it would be better to stop growing wet rice. The demand for vegetables is increasing in the region around Hanoi, and the extra income they would gain from switching permanently to vegetable growing would enable families to save more money for hard times.

According to chair of crop physiology Professor Paul Struik, the conclusion from this research should not be that wet rice growing everywhere in Vietnam or Southeast Asia should give way to vegetable growing. Wet rice growing is a centuries-old tradition that provides a reliable source of staple food in a wide area. It is however advisable, in areas where vegetable growing has been adopted successfully and where wet rice cultivation is done in combination, to look carefully at whether soil quality has started to go into a downwards spiral.

The research will be continued by a Vietnamese PhD student, who will be supervised by Everaarts, Struik and Dr Jacques Neeteson of Plant Research International. The objective is to optimise vegetable growing in the Dong Anh district, and to investigate whether farmers can earn enough from permanent vegetable growing to be able to buy their rice. / HB

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