To keep hunger at bay, rice experts turn to new fertilizer tecniques

A common Asian scene these days, and getting more common, is a cone-hat farmer throwing white crystals of nitrogen fertilizer over half-sunken rice paddies.

Without fertilizers, the new "miracle rice" varieties barely perform better than traditional strains. As developing Asian nations seek food self-sufficiency or expanded rice exports, they must increase farmers' dependency on central sources of urea, the nitrogen fertilizer made from natural gas.

If any constraint will limit Asia's Green Revolution, it may be in the high cost and fast-rising demand for petroleum-based fertilizers. In the last four years, the rice-growing nations of Asia have been forced to boost imports and build large manufacturing plants to obtain enough urea.

As much a 150 kilograms of urea can be used per hectare (132 pounds per acre) with the new seeds from the International Rice Research Institute (IRRI). That is seven times the amount used before the Green Revolution. The farmers' actual use, however, averages between 50 and 75 kilograms a hectare.

Urea prices are up to $200 a ton. That is lower than the $300 peak right after the 1973 Arab oil embargo, but the price is increasing faster than rice prices, taking a larger chunk of farmer income.

The new seed's most potentially damaging effect may be in the eventual loss of certain essential chemicals from the soils, caused in part by multi-cropping and massive application of the impurity-free fertilizers.

Urea, for instance, lacks the sulfur found in ammonia sulfate, which was the nitrogen source farmers used before switching to new rice varieties.In Indonesia , Bangladesh, and the Philippines, says Felix N. Ponnamperuma, an IRRI soil scientist, sulfur deficiency may already be limiting production.

Likewise, zinc losses have already put farmland out of production in many countries, creating a demand for soil testing and use of zinc-based fertilizer.

Rather than seek new urea sources, the rice institute's programs focus on changing farmer's fertilizer habits or seeking more natural nitrogen sources.

Sometime by the 1990s, institute scientists hope to introduce a double-cropping project whereby rice plants would be fertilized by neighboring plants that take nitrogen out of the air, a technique common to legumes.

In China and North Vietnam, farmers already aid rice fertilization with azollas, an aquatic fern that relies on blue algae in its leaves to "fix" the nitrogen. Even better, azollas can be fed cheap phosphorous to produce even more nitrogen. But the plant has yet to work in the warmer climates of Southeast Asia, IRRI agronomist Iwao Watanabe says.

Oddly, scientists have discovered that rice plants, when not ferlitized, can pull extra nitrogen out of the soil with the help of tiny bacteria associated with the roots. Rice researchers believe that such a process can eventually be improved upon to meet more of the plant's nitrogen needs.

In the meantime, however, scientists believe that farmers can improve urea efficiency. Only 15 to 30 percent of it ever gets used by the plant, with the rest evaporating, lost in the soil, or washed away.

Just a 1 percent increase in fertilizer efficiency would save 163,000 tons of nitrogen a year worldwide.

In some parts of Asia where labor is cheap, such as northeast India, peasants pack the fertilizer into mud balls with their thumb and place it directly at the plants roots.

The rice institute has encouraged farmers to time their fertilizer use more to the plant's growing period, which can add 10 percent to its effectiveness. But it's not catching on as fast as IRRI officials would like.

The brightest prospect is development of the "supergranule," a white, small ball of urea. When placed 10 centimeters deep between four rice plants, close to 70 percent of the fertilizer gets used. On farmers' fields, however, where conditions are less controlled, the effectiveness may be only 50 percent. Still , that's double improvement, reducing an expensive cost to the farmer.

Building special plants to mass-produce supergranules could take five years or more. In one Chinese province, however, villagers are testing the idea of taking the small urea particles commonly used now and pressing them into a large briquette, which also can be sunk into the rice paddy.

A Norwegian fertilizer firm called Norsk Hydro has pilot-tested supergranule production and reportedly is negotiating with Thailand to build a plant that would use the nation's new natural gas supplies.

Gaining farmer acceptance for supergranules may be the toughest task. "They understand the new varieties, but putting fertilizer down in the root zone is not something the farmer can easily see," says the IRRI director, Dr. Nyle C. Brady. Like other new farming techniques, the trick is setting up model farms and persuading the leading farmers to test the techniques.

Even more of a problem is whether IRRI should introduce machines that implant the supergranules, a labor-saving device that could upset countries where labor is in surplus. Fortunately, the device still needs more tinkering by engineers.