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How to Keep the Rice Bowl Full

A crisis looms. Water levels are falling, populations are rising. Asia faces a tough challenge: to keep the region fed by growing more rice with less water. Experts say the solution lies in developing a strain of rice which grows in dry paddies. Easier said than done


By David Lague/BEIJING

Issue cover-dated September 06, 2001


IF THERE IS an enduring image of East and South Asia it is probably the farmer, legs astride, bent at the waist, spearing emerald-green rice shoots into a flooded paddy field.

The paddy adjoins another and another and on to the horizon. Everywhere there is water. Together, these paddies make up a huge muddy ocean that sprawls across national borders and regional boundaries to cover about 11% of the world's arable land.

These rice-growing regions feed about three billion people each day--about half the world's population. But a crisis is looming that threatens this vital food supply.

It takes about 5,000 litres of water to produce one kilogram of rice under traditional cultivation methods. This when rapidly growing populations and new industry are competing for limited supplies of fresh water and, at the same time, polluting rivers and reservoirs.

This poses an immense challenge for farmers, governments and agricultural researchers because all the while demand for rice is rising.

"When you project forward 50 to 100 years, it will be one of the major issues for the world," warns Colin Piggin, crop-research programme manager with the Australian Centre for International Agricultural Research.

For Bas Bouman, water scientist at the International Rice Research Institute in the Philippines, it boils down to a simple proposition: "We need to produce more rice with less water," he says.

Already, authorities in China have moved to curb traditional rice cultivation in areas where water is in short supply for urban use. "Around Beijing, farmers are not allowed to grow rice in flooded fields," says Tang Shengxiang, IRRI's Beijing representative and a former plant breeder with the China National Rice Research Institute.

Competition for water has wider implications than the threat to rice production. In early August, Ramesh Thakur, vice-rector of the United Nations University in Tokyo, warned that disputes over water could lead to conflict between nations as water tables fall and shared river basins are heavily depleted. "Over the next 25 years, half the world's people will have difficulty finding enough fresh water for farming and drinking," he wrote in the International Herald Tribune.

For Bouman and his fellow researchers at the IRRI, the pressure is on to develop new strains of rice and innovative agricultural technology that will save water while maintaining or expanding yields.

If the past is any guide, he believes it is possible. "If we put the same effort into this that went into the Green Revolution in the 1960s we will get higher yields," he says. Between 1962 and 1978, world rice output doubled in a period now known as the Green Revolution. During that time, rapid advances in irrigation, plant breeding and agricultural-chemical use allowed dramatic increases in food production. Annual world rice production reached 596 million tonnes in 1999.

One basic, though unpopular, measure would be to make farmers pay for the water they use. Water use in traditional rice growing can be highly wasteful if paddies and canals are poorly designed and maintained, allowing water to escape. Excessive flooding can allow too much water to drain away through the soil or evaporate. "If a farmer pays for what he uses, it is a strong incentive to save water," says Bouman.

The drawback is that in some parts of Asia, governments are unwilling to impose water charges on farmers for irrigation which has traditionally been free.

However, pioneering schemes where farmers are billed for irrigation are already under way in parts of China where demand for water is pumping rivers dry. Look at the ecological impact of mankind on the Yellow River, which runs west to east across northern-central China. Rarely does the river flow through to its ocean outlet in Shandong province during the dry season.

Tang of the IRRI says many farmers in China now factor in irrigation fees when deciding on the viability of their crops.

EXPERIMENTAL CROP Improved efficiency and user-pay systems will no doubt lead to valuable water savings. But plant breeders are now striving for a major breakthrough that will allow farmers to grow what has been dubbed "aerobic rice" in tropical areas. This is rice that grows on dry but irrigated soil, just like wheat or barley, rather than in flooded paddies.

Early experiments of growing aerobic rice in China, Brazil and other places suggest up to half the amount of water is needed. And the quality of the rice is as good as rice grown using traditional methods. "I don't want to raise expectations," says Bouman. "The drawback is that conventional rice varieties can't be treated like this. We need to develop new rice varieties."

Experiments with new aerobic rice strains cultivated under dry-soil conditions returned good yields in the first season. However, the harvest slumped 20% in the second season, and even more thereafter in a phenomenon known as yield collapse.

Researchers are not sure how or why this happens, but they have found that it can be averted if rice cultivated like this is grown in rotation with other crops. More research is needed into the relationship between the rice plant, water, soil pests and nutrients to understand why the crop behaves in this way. China and Brazil are the world leaders in experimenting with aerobic rice strains.

IRRI researchers are now feeling the pressure. They aim to develop a tropical-rice strain that can thrive in dry soil within five years. By merely attempting to grow rice on dry soil in the tropics, they are challenging a fundamental assumption that these plants can only grow under flooded conditions. In reality, however, rice plants don't require more water for growth than wheat or barley plants grown in the same area.

The main reason rice is grown in flooded conditions is that farmers discovered over the centuries that standing water is an efficient, non-toxic weed killer.

Saturated soils are very low in oxygen, which is vital for cell growth. However, rice can thrive in these conditions because its leaves and stems have internal air spaces that channel the oxygen down to the roots. Weeds lack this capacity and struggle to germinate and survive.

So if farmers switch to growing aerobic rice they may need to increase herbicide use to control weeds.

Still, researchers have high hopes for aerobic rice because some strains of rice, known as upland varieties, are already successfully grown in dry soil. In most areas, these varieties are low-yielding, but with improved irrigation and fertilizer, harvests can be increased.

"There is potential with aerobic-rice cultivation to get reasonable yields with current varieties," says researcher Piggin. "The constraint is the supply of water."

He points to Brazil as an example where upland rice grown aerobically under spray irrigation returns yields of about 5 tonnes per hectare. That's about the same as the average yield from flooded-rice cultivation in the tropics.

In dry northern China, farmers cultivating upland rice can routinely harvest 6 tonnes per hectare from fields that are irrigated three or four times during the growing season.

Piggin believes that plant breeding will help develop successful aerobic rice strains for tropical areas. But, he says, water and crop-management techniques could also help make significant water savings while maintaining high yields.

The IRRI's Tang notes that experimental work in China has shown it is possible to return very good yields in tropical areas with conventional rice varieties if paddies are only flooded at specific points of the growing cycle.

At other times, the surface can be left dry as long as the crop is not exposed to extreme moisture. "At times, the yields are even higher than normal," he says.

In the short term, these advances offer considerable benefits for regions like China and India, where water shortage is most extreme. In the longer term, they could be the first steps in a revolution that allows a break with centuries-old agricultural practice.

-- Martin Thompson (, August 30, 2001

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