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It's All in the Mix
A team of agricultural scientists has found a simple, inexpensive way to substantially increase rice yields and overcome disease problems

By Carolyn Dedolph (cdedolph@adb.org)
External Relations Officer

GREEN HARVEST: A farmer from Jian Shui County in Yunnan Province harvests rice grown by using the mixture technique.

In what the New York Times described as a “stunning new result” from “one of the largest agricultural experiments ever,” thousands of rice farmers in the People’s Republic of China (PRC) are using a new way to control a major disease in rice without any chemicals. And in the process, they’re getting higher yields and increasing their incomes.

Scientists from the Philippine-based International Rice Research Institute (IRRI) and their collaborators around the globe led this landmark research, which was funded by the Asian Development Bank (ADB) through the Exploiting Biodiversity for Sustainable Rice Pest Management Project. IRRI is an autonomous, nonprofit institution focused on improving the well-being of present and future generations of rice farmers and consumers, particularly those with low incomes.

“The Project is a good example of public sector agriculture and natural resource research supported by ADB that targets the problems and constraints faced by poor farmers in Asia,” says ADB Manager Bradford Philips.

Using biodiversity to reduce crop losses from disease and pests has reaped significant benefits for poor farmers. “Their real incomes have increased through reduced spending on chemical inputs, their yields have increased, and the environmental benefits of decreased chemical use and increased biodiversity are shared by their families and the community at large,” Mr. Philips explains.

Low-Tech or High-Tech?

Three years ago, IRRI began working in the province with the Yunnan Agricultural University and the national agricultural research systems in Philippines, Thailand, and Viet Nam. In a massive, single-variety rice crop, such as that grown in the Red River Valley of Yunnan, a single disease such as blast could easily explode into an epidemic. After the pathogen adapted itself to the physiology of one plant, it could then easily attack the rest of the crop. But if there are dissimilar plants in the field, the pathogen is unlikely to achieve a population explosion.

By planting different types of rice alongside each other, the scientists found they could almost completely control the spread of rice blast, a disease that can cost the rice industry millions of dollars a year. Known in scientific circles as exploiting biodiversity for sustainable pest management, the idea is not new to many farmers. What is new, however, is the cutting-edge science involved in showing farmers how to use this strategy to achieve maximum effect.

In the PRC’s southern Yunnan Province, farmers were using huge quantities of fungicide to combat blast. “Sometimes they were spraying a single crop six or seven times,” says Tom Mew, head of IRRI’s Entomology and Plant Pathology Division and the project coordinator.

Field Experiments

A 1997 experiment on a few hectares (ha) suggested that interplanting varieties could control 92–99 percent of rice blast—and boost yields by 0.5–1 ton/ha. In 1998, 812 ha were planted with high-yielding hybrid rice and glutinous (sticky) rice varieties, four rows of one and one row of the other. The crop was sprayed with fungicide once. Yields reached 9 tons of hybrid rice and nearly 1 ton of glutinous rice/ha. Even more impressive was that, within the interplanted crop, the blast incidence fell to 5 percent from a level of 55 percent in the monocropped field, and the yield loss dropped from 28 percent to nothing.

In 1999, the area increased to 3,342 ha. Farmers boasted that interplanting provided them with about US$150 more income per ha. By the end of 2000, the scheme covered 42,500 ha, and had expanded to nine other provinces in the PRC. Plans exist to implement the scheme, with some modifications, in the Philippines, Thai- land, and other rice-producing nations.

Thousands of Yunnan farmers are now mixing varieties in their fields, claiming it not only reduces their reliance on chemicals and improves yields, but also increases their incomes.

According to IRRI Director General Ronald P. Cantrell, the Project could be considered “the most successful joint effort ever” by IRRI and ADB. The three-year Project, which was recently completed, created economical, safe, and sustainable strategies that reduce farmers’ dependence on pesticides. It also improved the capacity of collaborating scientists around Asia to use the biodiversity concept and tools for pest management research. A second phase is being proposed to capture the knowledge and tools generated in phase 1 and translate them into on-farm impact.

“Anyone who doubts the positive impact of institutions like ADB should go talk to the thousands of happier, healthier, and wealthier rice farmers in Yunnan,” Dr. Cantrell says. “Because of the committed support of ADB, we’re confident millions of poor rice farmers and consumers—not just thousands—could potentially benefit from this research.”

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