Integrating Rice Cultural Practices and Waterfowl HabitatUniversity of California, Davis   California's central valleys once contained 2 to 4 million acres of seasonal and semi-permanent wetlands, now mostly converted to anthropogenic uses, including agriculture. Only 300,000 acres are estimated to remain in natural wetlands. Rice (Oryza sativa) was introduced to the Sacramento Valley before the turn of the century and became established commercially in 1912. It is produced mostly on former wetlands - heavy, poorly drained clay soils of the valley floor which are relatively unsuited for other crops. The clear, warm summer days and dry growing season are highly favorable for rice production, making California the highest yielding rice area in the world. Statewide average yields have exceeded 9.5 t/ha (8,500 lbs/acre) with maximum yields exceeding 12.3 t/ha (12,000 lbs/acre).California's Central Valley was estimated to have concentrated 40 to 50 million migratory waterfowl in the late 1800s, and as recently as the 1970s 10-12 million birds migrated through the state. Even today, it supports 3 to 5 million waterfowl, the largest concentration in North America. These populations are increasing as habitat is restored both in their northern nesting grounds and in their southern over-wintering habitat. Emerging evidence suggests that when populations are low, nesting areas are most important, but when populations are high, the quality of over-wintering habitat is critical to subsequent reproduction. Thus, in recent years wildlife biologists have given increasing emphasis on the quantity and quality of winter habitat.In the early years of rice production, grain depredation by waterfowl made ducks and geese a major pest of rice farmers. In 1917, only five years after the first commercial rice crop in California, grain losses due to ducks totaled $1 million. In the 1940s, both the U.S. Fish and Wildlife Service and the California Department of Fish and Game expanded and developed the wildlife refuges, effectively reducing the problem of grain depredation by waterfowl. In the decade of the 1970s, semidwarf, lodging resistant cultivars were introduced to California rice culture. Not only were these cultivars high yielding, but they were largely photoperiod insensitive, shortening the growing season from 160-170 days to 135-145 days. Furthermore, soil leveling with laser-directed equipment was widely adopted, greatly improving water management during critical periods of seedling development as well as for field drainage and soil drying prior to harvest. With erect (nonlodged), short-season rice, uniformly dry soils and larger combines, harvest is now completed largely before migratory waterfowl arrive. Although primarily aimed at the improvement of agronomic efficiency in rice, these events greatly enhanced the possibilities for environmental stewardship with respect to the conjunctive use of rice production and overwintering waterfowl.California rice fields have long been a source of food and habitat for a large number of waterfowl species. An average of 350 lbs/acre of unharvested rice grain coupled with 250 lbs/acre of small invertebrates, tubers, edible shoots and seeds provide a food value nearly equivalent to that produced by natural wetlands. Thus waterfowl have become highly dependent on rice fields (and other grain fields) for food. While some farmers and hunting clubs have managed rice fields in the fall and winter to attract ducks and geese, only recently has the industry as a whole proactively embraced the idea of post harvest management of rice fields for their unique qualities as a waterfowl habitat.The Rice Straw Burning Reduction Act (AB 1378) of 1991, mandated the phase down of rice straw burning in the Sacramento Valley by the year 2000. Traditionally, rice farmers disposed of straw by burning, leaving about 70 % of the unharvested grain readily available to waterfowl on the soil surface. Except in very high rainfall years, most burned fields remained essentially unflooded in the winter although 7-10 percent were estimated to have been flooded for duck clubs. With changes in straw burning regulations, growers have coupled straw disposal to management for winter waterfowl habitat.Without burning, two options remain for rice growers: 1) in-field incorporation of straw, and 2) straw removal for other uses. While the latter would be preferable, the markets for rice straw are poorly developed and currently not competitive with other stocks for industrial uses. For the short term, growers have settled on methods for in situ disposal, varying in expense, but all more costly than burning. With the need to develop novel approaches to in-field disposal came the realization that moisture is essential to straw decomposition, especially in the warmer postharvest period of early fall. But flooded fields may become anaerobic, thus retarding decomposition. Initial proposals from the environmental community included the suggestion to flood all 500,000 acres of rice land to a depth of two feet, creating not only wetlands, but stored water to flush the delta and alleviate water shortages in general. This was impractical for several reasons: 1) diversion of limited water in the fall when moisture is most needed to enhance straw decomposition was at odds with the needs of river fisheries, most notably winter-run Chinook salmon; 2) the proposed high water depths were not suited for waterfowl use (most ducks forage in six inches or less floodwater and geese prefer unflooded fields); and 3) this depth of water could not be contained by the current rice field water management infrastructure. This dialogue between environmentalists, waterfowl conservationists, farmers and researchers led to an increased awareness of the potential for coupling waterfowl friendly winter flooding with innovative experimental techniques to manage rice straw. Most notably is the concept of "straw rolling," whereby fields are reflooded after harvest and the standing straw is mashed into the soil surface by large tractor-pulled cage rollers. Advantages of this method are that it is less costly than dry incorporation, most of the unharvested grain remains at or near the soil surface as compared to conventional incorporation with a stubble disc or plow, and the continuous flooding creates a habitat for invertebrate organisms which serve as high protein food for overwintering waterfowl.The long-term agronomic consequences of nearly year-round anaerobic soils created by the combination of winter flooding for straw disposal and in-season flooding for rice cultivation is largely unknown in temperate rice production, but so-called long-term yield declines are now widely recognized in the continuous rice cropping systems (2 to 3 crops/year) of tropical Asia. Considerable long-term research is currently in progress to assess and improve the sustainability of rice cropping systems in conjunction with the concept of managed wetlands. Meanwhile, California rice growers are experimenting with various methods of straw chopping, light incorporation, rolling and winter flooding to dispose of rice straw. Water suppliers, environmental groups and rice growers have clearly made a difference in improving winter waterfowl habitat and rice fields have become a highly visible and viable extension of managed wetlands and a public relations coup for the value of agricultural land.References:Brandon, D.M., S. Brouder, D. Chaney, J.E. Hill, J.M. Payne, S.C. Scardaci, J.F. Williams and J.E. Wrysinski. 1995. Rice straw management today and tomorrow. University of California and Ducks Unlimited. 6p. Hill, J.E., S.R. Roberts, D.M. Brandon, S.C. Scardaci, J.F. Williams, C.M. Wick, W.M. Canaveri and B.L.Weir. 1992. Rice Production in California. University of California Cooperative Extension, Division of Agriculture and Natural Resources, Publication 21498. 22p. Miller, M.D. and D.M. Brandon. 1979. Evolution of California rice culture. IN: Willson, Jack H. (ed.). Rice in California. Butte County Rice Growers Association, P.O. Box 128, Richvale, CA. Pp79-134. Reid, Frederic A. and Mickey E. Heitmeyer. 1995. Waterfowl and rice in California's Central Valley. Calif. Agric. 49(6):62. Brouder, Sylvie M. and James E. Hill. 1995. Conjunctive use of California ricelands enhances the value of agricultural land. Calif. Agric. 49(6):58-64. Blank, Steven C., Karen Jetter, Carl M. Wick and John F. Williams. 1993. Incorporating rice straw into soil may become disposal option for growers. Calif. Agriculture. 47(4):8-12. Miller, M.R., D.E. Sharp, D.S. Gilmer and W.R. Mulvaney. 1989. Rice available to waterfowl in harvested fields in the Sacramento Valley, California. Calif. Fish and Game 75: 113-123. |
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