Every year, soon after harvest, we flood our rice fields. The practice is part of our holistic approach to farming. Flooding helps to naturally break down the rice straw so that the field will be ready to work up for planting the following spring. The standing water helps with decomposition of the plant material left behind, which enriches the soil for the next year’s crop. It also provides habitat for a variety of species of seasonal migrating ducks, geese, and shorebirds that are traveling along the Pacific Flyway. Flooding usually starts in November and lasts for several weeks. We then allow the fields to dry out naturally through evaporation and soil absorption. This year, working with California Trout and the University of Califonia at Davis, we are changing things up a bit and will be creating a new winter “crop”: fish food.
In summer, plants growing on the floodplain convert carbon from the air and solar energy into plant biomass. In winter, sunlight falling directly on the water is captured by phytoplankton (algae) floating near the surface of water. Either way the floodplain must inundate in order to get this floodplain carbon, which is the foundation of the aquatic ecosystem’s energy supply, into the water. Wide and shallow floodplains capture many times more solar energy than do narrow, deep and dark river channels confined by levees. Winter-inundated floodplains were, in essence, the “solar panels” that powered the Central Valley’s aquatic food web.
Today more than 95% of Central Valley floodplains are cut off from their river channels by levees. Whereas the pre-development Sacramento Valley was a mosaic of low-gradient, relatively shallow wetland habitats that drained slowly, now the farm fields that have largely replace them are engineered to drain efficiently, shedding high volumes of storm water quickly through drainage canals. This rapid, high-volume drainage system is the antithesis of the historic prolonged, broad and shallow annual inundation of the pre-development Central Valley. As a consequence today’s aquatic food web receives only a tiny fraction of the energy input it once did. Essentially, levees are starving salmon and smelt populations by depriving the river ecosystem of the photosynthetic food source that is the foundation of the aquatic food web.
River Garden Farms can help solve this problem by demonstrating how to create fish and bird habitat and grow food for fish and wildlife all while maintaining profitable agricultural production on the same lands.
On November 1, we began a new practice. While very similar to our traditional one of systematically flooding recently-harvested rice fields to mimic wetlands, this year we will not be letting the fields dry out. Instead we will maintain a consistent depth of about 8 inches for a period of 3-4 weeks before draining the water– now with tons of fish food–back into the river. The cycle will be repeated two or three more times through the end of February 2017, with a fresh ‘batch’ of fish food generated each time. All the while, soil-enriching decomposition and wildlife habitat will continue to occur as usual.
Throughout these months, weekly water samples will be procured and taken back to the lab at UC Davis to test plankton levels. The first of these visits occurred earlier this week. Jacob Katz, (Senior Scientist at CalTrout), Carson Jeffres, (field and lab director of the UC Davis Center for Watershed Sciences) and UC Davis researchers Miranda Tilcock and Eric Holmes scoped out the fields for the ideal sampling spots and took initial samples.
-Special thanks to Jacob Katz for contributing to this post