New research findings from the University of California, Davis, are confirming rice farmers' long-held belief that waterfowl and rice farming go well together in the heart of California's former wetlands.

In a study to be published in the journal of Agriculture, Ecosystems and the Environment, researchers found that foraging waterfowl in winter-flooded rice fields helped control weeds and increase the decomposition of rice straw from the previous season's crop.

"Our results demonstrate that there are instances in which wildlife and agriculture not only can co-exist, but are actually of mutual benefit," said lead researcher Chris van Kessel, professor and chair of the UC Davis Department of Agronomy and Range Science. "This is a welcome departure from the previous line of thinking that waterfowl and rice-farming interests could not equitably share wetland habitats."

In rice fields that were flooded during the winter and open to foraging waterfowl, the researchers found that rice straw decomposed more than 30 percent faster and grassy weeds in the subsequent growing season decreased by more than 50 percent, compared to flooded rice fields where wildfowl were fenced out. Furthermore, grain yield was not reduced by the foraging ducks.

This new report is the first on-farm study of the impact of waterfowl on winter-flooded rice fields. An interdisciplinary team of UC Davis scientists composed of soil scientists Jan-Willem van Groenigen and Willi Horwath, wildlife biologists John Eadie and Ed Burns, and agronomist van Kessel was put together for the project.

The study was conducted on 15 winter-flooded rice fields along a 65-mile stretch of farmland in the Sacramento Valley. It confirms findings of a study conducted two years ago by UC Davis researchers in experimental plots rather than actual farm fields.

In California, rice is grown on approximately 617,500 acres, mostly in the Sacramento Valley. Thanks to a nearly ideal combination of moderate temperatures, sunlight and readily available water and nutrients, California rice yields are among the highest in the world.

The downside of that success story has been that the rice fields have replaced natural wetlands, as is the case in many parts of the world. For example, Europe's wetlands have been reduced by 10 percent-15 percent their original size, and wetlands in the contiguous United States have shrunk to about half their original size, with large parts of those wetlands converted to rice fields. Since the 1780s, California has lost 90 to 95 percent of its wetlands.

Historically, wetlands have played a critical role in providing habitat for a vast array of wildlife, including waterfowl. It's estimated that the Sacramento Valley's natural wetlands provide winter habitat for up to 20 percent of all of the waterfowl in North America and up to 60 percent of the wintering waterfowl in the Pacific Flyway. The decline in the size of the wetlands has threatened the vitality of those wild populations.

Ironically, winter flooding of rice fields -- employed as a possible solution to a rice production problem -- appears to help ease the loss of wetlands for wildlife.

For years, rice farmers routinely burned their fields each fall to get rid of the rice straw left behind after the grain was harvested. But air pollution concerns led to state legislation that now limits rice-straw burning to 25 percent of California's total rice acreage. It's anticipated that burning will decrease even more in the future.

Winter flooding of rice fields is one technique farmers have turned to in recent years as an alternative to burning the straw. It's been demonstrated that flooding of the rice fields during winter speeds decomposition of the rice straw and reduces the amount of tilling required in those fields in spring.

Encouraged by the findings of this most recent study, van Kessel and colleagues note that more research is needed to determine how the impact of foraging waterfowl is affected by different techniques, like disking and rolling, that farmers may use to manage rice-straw after harvest. And they point out that the type of rice harvester used could influence wildfowl activity in the flooded fields.

The researchers also suggest that the mutual benefits for wildfowl and rice farmers might be realized in other rice-growing areas of the world with temperate climates, such as the Mediterranean and Japan. They note that the advantages of ducks in the winter-flooded fields might be particularly significant for organic rice farms, which don't use pesticides and herbicides.

The waterfowl-and-rice study was funded by Ducks Unlimited and the USA Rice Federation.