PARENT SESSION
Oral Session #60: Agroecology- Sustainable Agriculture.
Presiding: R. Bohanan
Wednesday, August 7. 8:00 AM to 11:30 AM. Mesquite Room, Radisson.

California rice fields: Fertile ground for the adoption of environmentally friendly management practices.

Hartley, Christopher^*,1, van Kessel, Chris¹, ¹ Department of Agronomy and Range Science, Davis, CA

ABSTRACT- Ideal growing conditions coupled with state-of-the-art equipment and management practices have placed California rice yields among the highest in the world. However, growers have faced increased scrutiny over the impact on non-target organisms and the environment. In 1991, legislation was passed to greatly restrict the burning of field residues, requiring rice farmers to adopt alternative methods of straw disposal for the more than 200,000 hectares of rice grown in the Sacramento Valley. Despite lingering fears over the impact on weeds, diseases and invertebrate pests, nutrient availability and overall yield, most have turned to residue incorporation, often in conjunction with winter flooding. Consequently, the rice fields have become vast, mosaic of seasonal agricultural wetlands that serve as supplementary habitat for the flora and fauna found in natural wetland systems. Additionally, it has provided a unique opportunity to study the impact of management practices on rice field community systems. Winter flooding and straw management practices were compared at the Long-Term Alternative Rice Straw Management Practices Project in California. Changes in management increased resource availability during winter months resulting in earthworm (Sparganophilus pearsei) population densities greater than 1000 / m² and associated increases in crayfish (Procambarus clarkii) populations. Similarly, winter flooded fields attract large numbers of water fowl, which may also feed on the invertebrates. Using stable isotope data, we observed a 6 per mil decrease in delta N-15 values for crayfish found in rice fields when compared to the adjacent irrigation canals, suggesting that differences in crayfish delta N-15 values, which reflect feeding habits, may be used to follow migration habits within the wetland system. Additionally, the potential for greater reliance on naturally occurring biological communities to influence nutrient cycling and regulate pest populations will be discussed.

KEY WORDS: Rice, Isotopes, Invertebrates, California