Integrating agronomic management practices with waterfowl populations in rice fields: opportunities and mutual benefits

Rice production in California is largely concentrated in the Sacramento Valley. Before the land was converted into rice production, the valley was largely composed of interconnected wetlands that were inundated in the winter months when most of the rainfall occurred. Numerous ducks, geese, swans, and shorebird species winter in the Sacramento Valley as they migrate each fall from the northern regions of the western part of the United States and Canada. Following the conversion of the wetlands into rice production in the early 20th century, the winter habitat for waterfowl changed significantly. California rice production is considered to be one of the highest in the world and grain yields of 12 t ha-1 paddy rice are no exception. High grain yields are always associated with high residue yields as the harvest index for rice remains close to 0.5. Whereas in the early days residues were burned in the fall or spring, new regulations will reduce the area that can be burned to 25% of the total area used for rice production. As off-site use for rice straw remains limited, on-site disposal is often the only option left for farmers. To accelerate the decomposition process of the residue, almost half of the total rice production area in California is reflooded during the winter. Once the straw is dispersed across the field in the fall, the fields are flooded in late October or early November and drained again in early spring to allow preparations for seeding. By providing alternative habitat during the winter, the rice fields attract large numbers of waterbirds, which use the fields mainly to forage and roost. When many birds visit rice fields, the extra disturbance they induce may increase the rate of decomposition of the rice straw. Early findings from an enclosure study suggest that indeed waterfowl enhanced decomposition. Because waterfowl forage on rice seeds and on weed seeds present in the rice fields, the waterfowl population may also affect the size of the weed seed bank. Depending on tillage practices, a reduction in weed herbicide use could also be anticipated. Along similar lines, the invertebrate population in the soil would also depend on the size of the waterbird populations that visit the winter-flooded fields. The effect of a reduced invertebrate population on nutrient cycling remains unknown. Fully integrating rice agronomic practices with waterbird biology remains a largely unexplored area. Although rice management practices and the ecology of wildlife in rice fields have been studied independently, integrated research should be conducted to understand the influence of management on rice production and the health and reproductive capacity of waterbirds. The classical agronomic research design will have to be replaced with a design that can verify how the frequency of waterfowl visits to rice fields affects agronomically significant parameters such as the rate of decomposition of rice residues, pest occurence, and grain yield.