Distribution of rice acreage in California by county. Low relative humidity throughout the growing season reduces the development, severity, and importance of rice diseases. However, cool weather and strong winds during stand establishment may cause partial stand loss and seedling drift. Figure 3 . Seasonal average rainfall and temperature patterns in the Sacramento Valley of California.
Hatched area indicates the California rice production season from seeding to harvest.
Rice is grown mostly on fine-textured, poorly drained soils with impervious hardpans or claypans. A few of the soils are loam in the surface horizon but are underlain with hardpans. These soils are well suited to rice production, since their low water permeability enhances water use efficiency. Most of the irrigation water for California rice comes from winter rain and snow-fed reservoirs of the Cascade, Klamath, and Sierra Nevada mountain ranges. Less than 10 percent of rice irrigation water is pumped from wells in areas where surface water is not available, or as a supplement to surface supplies.