It's an essential part of the armory. Yet, Dr. Wolfe said, even organic farmers underuse diversity, as they also have been indoctrinated in the simplicity of and seduced by the universality of monocultures. Some of the obstacles to using different varieties include the extra work of keeping track of and maintaining a diversity of plants that can require different kinds of tending and harvesting. If kinds of crops require different harvesting methods or are harvested at different times, it can increase the effort a farmer must expend in a given field. In Yunnan province, farmers harvested rice grains by hand, making it simple to gather and sell the two rice varieties separately.
Some scientists argue such problems can also be overcome with mechanized harvesting.
In the Pacific Northwest where an increasing number of farmers are using mixtures of wheat to increase yields and cut down disease, growers may choose varieties that differ in useful qualities, such as resistance to disease, but that can still be harvested and sold together. Researchers say the study's implications extend to prairies, rainforests and other natural ecosystems. Just as the new study examines the role of a diversity of crops in fighting disease and in productivity of a rice paddy, biodiversity studies have been examining whether increased species number can affect such things as the health of plants in natural settings. So far the two kinds of studies appear to support one another well. For example, Dr. Tilman and Charles Mitchell, an ecologist at University of Minnesota, have found evidence in prairie ecosystems that an increased diversity of plant species decreases the incidence of disease.