Rice Management Systems for Water Quality Research Project: 2006-2008
Funded by SWRCB Proposition 50 Funds
Introduction, Background and Overall Objectives
Rice production in the Sacramento Valley has led to some concerns in water and air quality. Field management changes include the incorporation of straw residue, over-winter flooding of rice fields, and new crop establishment methods. The impact of these practices on water quality was not known. Nitrogen, phosphorus, and organic carbon losses to surface waters can lead to degradation of surface water quality, alteration of surface water ecosystems, and negative interactions with water treatment practices for public consumption. Our research study addressed these issues. Both plot level and field level experimental sites were used. Plot studies were set up at the Rice Experiment Station to evaluate the effects of alternative crop establishment methods (to control herbicide resistant weeds) on water quality. On-farm research was conducted throughout the Sacramento Valley to evaluate the effects of straw incorporation (burn vs. incorporation) on water quality.
Changes in In-Field Straw Management
The project examined the impact of the phase-down of rice straw burning on water quality. Legislation in 1991, aimed at improving air quality, resulted in rice farmers adopting alternative methods to dispose of straw. General disposal methods include soil incorporation by conventional tillage (plowing the straw into the soil) followed by winter flooding, and going over the field with a heavy roller to press the straw into the soil, known as wet rolling. Winter flooding is particularly important, providing over 250 thousand acres of wetland habitat for over-wintering waterfowl in the Pacific Flyway. By either method of straw incorporation, the average straw-return rate is about four tons/acre. The decomposition of this increased soil carbon and nitrogen may lead to a concomitant increase in organic carbon and nitrogen in ricefield drain water. In cooperating farmer’s fields, we examined whether or not rice straw management practices have an impact on drainage water quality in terms of dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) loads. in the seasonal outflow patterns of DOC from rice fields. This was particularly relevant since DOC is a CALFED drinking water constituent of concern.
Changing Rice Seeding Practices
Rice seeding is gradually changing from conventional water-seeding to various forms of dry-seeding (i.e., stale seedbed drill-seeding and spring-tilled dry seeding) in response to herbicide-resistant weeds and rising costs. These emerging management systems require different water management and fertilization methods compared to conventional water-seeding. We evaluated outflows for nutrient, sediment and carbon loading associated with different seeding methods. We evaluated whether dry-seeding lowers the need for into-the-water herbicides such as granular thiobencarb and the pyrethroids used for rice water weevil control. With dry-seeding this may not be required at the same levels, or at all, since weevils don’t oviposit in non-flooded fields.
Changes in Weed and Pest Management
The study compared conventional till systems with minimum till/stale seedbed systems to determine the impact on weed emergence, and the need for fertilizer and herbicides associated with each to attain optimum yields. We evaluated new chemicals (as well as thiobencarb) in use, pest management practices associated with them and their impact on water quality. Though pesticides are not listed as a CALFED drinking water quality program constituent of concern, our investigation of production practices that may reduce their use addressed two areas of need articulated by the Regional Water Quality Board, off-flavors and waste discharge.
Technical Advisory Committee Steakholder Input
Early in the project, a Technical Advisory Committee was convened and members were consulted throughout the project. The Technical Advisory Committee consisted of experts in the rice industry from Sacramento Valley Water Quality Coalition, Ducks Unlimited, Inc., California Rice Commission, Rice Research Board, Natural Resource Conservation Service, Colusa Indian Community Council, Department of Pesticide Regulation and Glenn-Colusa Irrigation District. Two annual meetings were held.
Objectives
The primary objective was to determine the concentration and load of various solutes in drain waters coming from rice fields throughout the year as impacted by various crop establishment methods and straw management practices. Among these management practices we determined, from plot and field level outflows: (1) the concentration and amount of total carbon (organic and inorganic), dissolved carbon (organic and inorganic), nitrogen (nitrate and ammonium), orthophosphate (total and dissolved), potassium, and copper; (2) water chemical, physical, and biological properties such as dissolved oxygen levels, total dissolved solids, electrical conductivity, turbidity, and Ecoli concentrations; and (3) pesticide concentrations and loads in rice field outlet drains. Solute concentrations and water properties were be determined on the inlets to the rice fields and in the peripheral drains downstream of the rice field water.
Based on these studies, various management approaches have been compared and suggestions for applying them have been made to California rice growers. These practices intend to reduce the outflow of soil nutrients and environmental contaminants from rice fields while controlling weeds and invertebrate populations.
The final report discusses rice field management systems, including various alternative practices related to in-field straw management, water management, seeding methods, weed management, and pest management.
Outreach and Implementation
Overall, this project provided technical information to, and generated interest among, rice farmers, irrigation district managers, pest management and crop consultants and others in the rice industry in the watershed area, particularly in the participating counties. This is critical to increasing grower awareness of management options to consider, under each unique set of circumstances on a given property. The goal to optimize water quality must be weighed along with other concerns such as managing financial risk and providing sufficient wetland resources for wildlife.
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