Air Quality Water & California Rice Pesticides Rice Straw Wildlife

Environmental & Conservation Balance Sheet for The California Rice Industry

Chapter 2: Water Supply in Relation to Rice Farming

The purpose of this water supply chapter is to document the water supply issues associated with rice production in California. The background material for this chapter was the white paper Water Use for Rice Farming in California (CH2M HILL, 1992). New information pertaining to recent initiatives, regulations, monitoring results, and other water supply issues were reviewed and documented in this chapter.

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Background

Irrigation is essential to rice cultivation. Although rice is grown in some parts of the world without benefit of irrigation, this would be impossible in California. Furthermore, flooded rice culture is universal in California. Again, rice is grown without flooding in many places, but this results in greatly increased weed control costs, lower yields, and much less efficient use of fertilizer nitrogen. Some of the most striking features of water use for irrigated rice farming in the Sacramento Valley are the following:

• Approximately 2.23 million acre-feet of California's water (about 2.6 percent) is used to irrigate rice.
• One can see the water in a rice field for much of the growing season.
• While the water itself is visible, one cannot see the degree of efficiency with which water is being used, or the many benefits from the field's produce.

Major questions regarding water use in the cultivation of rice are:

• How much of California's water is used to irrigate rice?
• How is the water that can be seen standing in rice fields used, and what efforts are being made to use it efficiently?
• Where does the water go when it leaves the rice field?

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California's Rice Crop

In California, commercial rice was planted on about 100,000 to 150,000 acres from 1920 to 1940 (Hill et al., 1992). With the onset of World War II, rice production acreage increased and eventually expanded to a peak of about 608,000 acres in 1981 (Hill et al., 1996). With substantial fluctuations (because of changing market conditions), today about 450,000 acres are devoted to rice production. Most of this land is in the Sacramento Valley, as illustrated in Figure 2-1. California's Mediterranean climate is warm and dry with clear days and a long growing season, which is ideal for rice production. The expanding need to conserve water has driven California's rice production to acreage with poor drainage that is generally unsuitable for other crops. California rice is grown on heavy clay soils of river valley floors and on eroded terrace soils on the Valley's rim (Hill et al., 1996). These soils restrict deep percolation, which can reduce the amount of water that must be applied to produce a rice crop.

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Quantity of Water Used for Irrigation of Rice

A comparative disposition of California's average annual water supply is presented in Figure 2-2. This figure illustrates that agricultural water use has increased only 4 percent, while environmental and related uses have increased 27 percent since 1960. In the Sacramento Valley region, agricultural water use is expected to decline over the next 30 years as irrigation efficiencies continue to improve. Future rice acreage is difficult to project because many complex market and political forces will affect the industry. In this report, California's water supply is considered as the sum of:

• California's runoff: precipitation that falls onto California and does not soak into the ground, evaporate, or flow into another state
• Runoff from other states that flows into California
• Groundwater that is pumped for use in California

Figure 2-3 illustrates the approximate annual water use for rice irrigation in California. The left-most bar labeled "California's Water" shows that just over 60 percent of the total volume of 85 million acre-feet in a normal year (an acre- foot is the water required to cover 1 acre [43,560 square feet] to a depth of 1 foot) is used for environmental applications or is undeveloped (not captured by diversion or storage). Of the remainder, most is used for agricultural and urban purposes. Approximately 2.23 million acre-feet per year, or about 2.6 percent of California's total water supply, is applied to rice fields as irrigation water. It is important to realize that 25 to 35 percent of this amount is returned to the water resource system. Outflow irrigation water is either reused, percolates to groundwater, or drains back into rivers, thereby conserving water that could otherwise be lost from future beneficial use.

While 2.6 percent is not a large figure, it nevertheless represents a significant volume of water, and it is therefore critical that rice farmers put this resource to efficient, beneficial and justifiable use.

A schematic representation of the flow of water to and from typical rice fields in California is illustrated in Figure 2-4. Figure 2-3 illustrates the same waterflow as Figure 2-4, but it gives a clear picture of how much water is flowing in the various parts of the rice agronomic system.

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Sources of Water for Rice Production

The water used for rice production comes from a variety of surface-water sources and from groundwater. Many of the Sacramento Valley's rice farms diverted their water from the Valley's rivers and streams before the local, state, and federal governments began to develop the region's water resources. When federal and state water development took place (primarily the Central Valley Project and the State Water Project), only a relatively small portion of the newly developed water actually went to development of new rice farms. Today, because of the complex and dynamic network of water resources serving the region, it is difficult to identify the exact proportion of rice acreage that receives water from federal, state, and other sources. The bar labeled "Source of Water" in Figure 2-3 shows the approximate relationships of these quantities derived from general facts about acreage and water project distribution; however, no specific numbers have been attached because of uncertainty about the exact volumes.

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How Water is Put to Use

Agricultural water use is primarily for irrigation. Once water is applied to the field, as depicted in Figure 2-4, what really happens to it? In general, water applied to rice fields is used in one of three ways:

• Some is evaporated from the plant, water, or moist soil. This process is called evapotranspiration.
• Some percolates below the root zone and recharges groundwater. This is called deep percolation.
• Some flows out of the field. This may be recycled into other fields, or returned to rivers or streams for downstream uses.

The bar labeled "Fate of Water" in Figure 2-3 shows approximately how much water leaves the rice field by these routes. The largest portion of applied water, approximately 64 percent, is evaporated or taken up by the plant and transpired (Jack Williams pers. comm., 1991). This amount cannot be easily reduced, and it will vary directly with the rice acreage. Approximately 9 percent flows out of rice fields and is reused for irrigation of other rice fields. About 27 percent percolates into the soil and recharges groundwater, and about 5.5 percent flows out of the rice field as surface water and is not reused for rice irrigation. This surface water and groundwater is reused for many purposes. In summary, water that leaves rice fields flows into a network of water supply sources and is generally not "wasted."

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Changes in Water Use Over Time

How has water use for rice irrigation changed over time? Figure 2-5 shows the trends of rice acreage, average crop yield, and average water use per acre.

Rice yields have changed significantly since it was first grown in California (Hill et al., 1992). From 1910 to 1955, average rice yields were between 2,500 and 3,500 pounds per acre. Between 1955 and 1990, there was a relatively steady rate of increase, approximately 143 pounds per acre each year. Yields are currently averaging over 8,000 pounds per acre, with the 1994 crop yielding about 8,500 pounds per acre. This makes California one of the most productive rice-growing regions in the world. California rice growers currently lead the world and United States rice producers in average yield of commercial rice (in a single, annual crop) as illustrated in Figure 2-6. As average yields have increased, the average production water use efficiency has improved considerably, as illustrated in Figure 2-7.

These increases in rice yield and decreases in applied water can be attributed to many factors.

California rice farmers have levied a tax on themselves to build and maintain a successful cooperative agricultural research program. This has assured them strong scientific support to address industry challenges.

The California rice farmer's research program (in cooperation with the U.S. Department of Agriculture and the University of California) has developed improved varieties that efficiently use sun, water, and fertile soil in rice cultivation. In general, today's rice plants are shorter, resist many major diseases, establish themselves in the rice field more vig orously, mature more quickly, and have better grain quality than their predecessors.

California farmers have identified improved cultural (farming) practices that allow rice yields to approach the maximum potential of the rice plant. Rice farmers and scientists have "fine tuned" management of soil fertility, weeds, diseases, and water to a great extent.

During the same period in which productivity has increased, water use per acre has declined significantly (Williams, 1991). As shown by data from individual rice fields in the Glenn-Colusa Irrigation District, water application averaged about 8.9 acre-feet/acre for the 10 years prior to 1972. The average for the next decade was about 7.9 acre-feet/acre. Since 1981, the average has been estimated to be about 5.5 acre-feet/acre (Brandon, 1991), a 38 percent decrease from the level of water applied during the 1960s. So, during the last 30 years, these rice farmers have apparently used 38 percent less water to grow almost twice as much rice. It is also important to understand that about 2 acre-feet/acre of the applied water returns to the system as outflow into surface waters and percolation to the groundwater (Brandon, 1994), and is therefore available for further use. Because there is no comprehensive documentation of the unit use of water for the full California rice acreage, the University of California Cooperative Extension is currently conducting such research.

A number of innovations have contributed to this reduction in the unit amount of water applied to rice in California.

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Precision Leveling of Rice Fields With Laser-Guided Equipment

It is critical to maintain a minimum water depth of 4 to 6 inches during most of the growing season to provide an optimal rice growing environment. Doing so greatly facilitates sub sequent management practices for stand establishment, weed control, and field drainage for harvest. Small imperfections in the field surface can result in the need to divert more water into the field to maintain this minimum depth uniformly in the field. Precision leveling allows the farmer to achieve and maintain this depth uniformly throughout a field with less water. Laser land leveling also decreases the number of levees required and increases productive land area and machinery efficiency.

After the adoption of laser land leveling technology in the late 1970s, more than 90 percent of California's rice land was precision leveled, increasing the farmer's ability to conserve water (U.C. Cooperative Extension, 1992). This technology increased rice growers water management capabilities and allowed them to take advantage of the advent of improved semi- dwarf rice varieties with early maturity (Brandon, 1994).

Development of Early Maturing Varieties

Growing rice that matures more quickly shortens the season during which irrigation water is required. Plant breeding for commercial rice has led to the development of varieties with maturities ranging from a 160- to 165-day cycle to about a 130- day cycle. Perhaps one additional week gain in early maturation can be achieved before grain quality is sacrificed (Brandon pers comm., 1996).

Semi-dwarf rice varieties with high grain yield and quality have been developed. Under best management practices (precision land leveling, effective pest control, etc.), these varieties produce the current average California grain yield of approximately 8,300 pounds per acre of high quality rice (Brandon, 1994).

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Development of Water-Conserving Irrigation Systems

State mandates currently require rice growers to hold herbicide-treated waters on their fields to allow dissipation or breakdown of herbicides into nontoxic products. For this reason and to improve water conservation, several innovative water management systems have been developed by rice growers in the Sacramento Valley. Therefore, water-holding requirements have made it necessary for farmers to control water flow more carefully, and in the process, many have learned to use less.

Three main water management systems are currently being used by rice growers: conventional, recirculating, and static systems, as illustrated in Figure 2-8 (Hill et al., 1991).

• In the past, almost all rice farms were irrigated with conventional flow-through systems where water flows into one "check" or basin (a rice field is subdivided into checks by levees) and then to the next check. Finally, the water flows out of the bottom check and into a drain. It has been estimated that 20 percent or more of the applied water with a conventional system is spillage (U.C. Cooperative Extension, 1991). Conventional system water management problems have made it increasingly difficult for rice growers to comply with the required water-holding periods (U.C. Cooperative Extension, 1995).

• Closed systems, such as the recirculating and static systems, are considered to be best management practices for holding treated water because they can reduce pesticide residue mass discharge by up to 97 percent over conventional systems (Scardaci et al., 1994). Additionally, they provide improved water management flexibility that can contribute to water conservation efforts:

  • In recirculating systems, water is pumped from the bottom check back to an uphill field, usually on the same farm. Some of these systems have been implemented at the irrigation district level, but most have been built by individual farming operations.

  • A static system independently controls inflow into each basin and limits it to the amount required to replenish applied water lost to evapotranspiration and percolation. It also eliminates the possibility of spillage of field tailwater into public drains. This is a recent innovation and precise water management is easier than with other systems (U.C. Cooperative Extension, 1991).

Rice growers are adopting closed systems in an effort to improve water quality of rice field drain water according to a recent study: Rice Water Management Adoption Trends In California (U.C. Cooperative Extension, 1995). This study encompasses four major rice growing counties (Colusa, Glenn, Yolo, and Butte). Results from the four-county area show an increase in closed system usage from 74,600 acres in 1991 to 136,200 acres in 1994 as illustrated in Figure 2-9, a 58 percent increase in closed systems. However, the total number of acres in rice production also increased during the same time period (see inset, Figure 2-9). Of the total acreage, closed systems increased from 31.8 to 36.5 percent between 1991 and 1994, while conventional systems decreased from 68.2 to 63.5 percent, as illustrated in Figure 2-9. The substantial acreage converted to closed systems is an indication of the commitment of rice farmers' resources to meet the water quality and conservation challenges before them.

A summary of the rice test field data generated from GCID's "Water Conservation Through Water Use Understanding" program over the last 10 years shows a reduction in applied water for both conventional and closed systems. This trend is illustrated in Figure 2-7. Closed system inflow improvements since 1991 are depicted (GCID, 1995). However, the context and implications of GCID's water conservation program, referenced in page 2-14, must also be considered. A federal injunction issued against GCID seriously curtailed the GCID's ability to divert irrigation supply water through the defective fish screens at its main pump station. This curtailment was responded to by GCID's implementation of a conservation program that penalized growers who released water from fields during certain periods of the growing season. Although this dramatically reduced total applied water to rice fields, there is evidence that continuing this progam at its present level may cause salt accumulation and reduce rice yields. Therefore, the GCID's conservation plans may change, and the trend of decreasing amounts of applied water may stop at applied water levels greater than those currently observed in GCID.

The extent to which improved rice varieties and cultural practices have specifically influenced water use for rice production in California has not been extensively studied (Brandon et al., 1996). Estimates based on agronomic practices, water use, and rice varietal changes over time show a dramatic decrease in net water use for rice production since the advent of earlier maturing, semi-dwarf rice varieties, precision land leveling, and improved water management with water-holding periods (Brandon, 1994).

How does this level of water use compare with that of other crops? For the purposes of this chapter, the following considerations are used for comparison:

• All of the water applied to rice fields (except for recycled water-see Figure 2-3) is considered. The best current estimate of this amount of water is approximately 5.5 acre- feet of water/acre (Brandon, 1991).

• The food value of the product is considered. The tonnage and dollar yield could also be considered; however, food value is an objective indicator of how the product satisfies one of peoples' most basic requirements, energy from food.

Figure 2-10 shows the number of cups of water required to generate a calorie of food energy for several crops. Water used on the farm and in food processing is included; water for preparation in the kitchen is not. Figure 2-11 shows the gallons of water required to produce a typical home serving of various foods (Krieth, 1991).

Rice is an efficient converter of water to food energy, com pared with representative vegetable, fruit, and nut crops as well as dairy products. Some of the grain is polished during additional processing of brown rice to white rice, so white rice appears less efficient because of additional water used in the milling process. However, this food energy is recovered when the polishing byproducts are used for various purposes.

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Conclusions

The following sections present the justification for ratings of the rice industry's performance relative to the environmental value of water supply.

Land Preparation

Flood irrigation of rice fields requires that levees be constructed and maintained. This permits the fields to function as water storage, flood control, and groundwater recharge facilities, providing additional flexibility in water supply for environmental and other uses. This beneficial aspect of land preparation is unique to rice farming, and requires additional effort by farmers.

Irrigation

Rice farming was established in lowlands near California's rivers. Historically, these areas were usually flooded during the winter and springtime, providing thousands of acres of wetland habitat. There are many environmental and economic benefits of maintaining this condition. These include floodwater retention, water storage, groundwater recharge, wildlife habitat enhancement, and stabilizing stream flow levels.

Initial flooding and flushing of rice fields require plentiful water early in the growing season. Water availability is typically good at this time of year, which minimizes the overall impact on water supply. Alternative crops, which in many cases are impractical on rice farmland, would generally use less water during this period.

Maintaining the necessary water depth in the paddies requires more diverted water during the early spring, but the amount of water ultimately consumed is similar to other crops, and less than most on a per-serving basis. Regional hydrology is such that diverted water that is not consumed by the rice crop returns to the water supply as runoff or groundwater.

Winter flooding provides additional water storage and some groundwater recharge during periods when reservoirs are generally at high levels. This has the effect of increasing the water supply available for other uses.

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References

• Brandon, D. Marlin. 1991. Rice Water Management. Rice experiment station.
• Brandon, D. Marlin. 1994. Influence of Rice Varieties and Cultural Practices on Water Use in California Rice Production. Rice Experiment Station.
• California Department of Food and Agriculture. 1995. California Field Crop Statistics for 1994. Sacramento, California.
• California Department of Water Resources. 1987. California Water: Looking to the Future. Bulletin 160-87. Sacramento, California.
• California Department of Water Resources. 1986. Crop Water Use In California. Bulletin 113-4. Sacramento, California.
• California Department of Water Resources. 1994. California Water Plan Update. Bulletin 160-93. Sacramento, California.
• California Department of Water Resources. 1996. Agricultural Land and Water Use for 1991-1994 Data. Red Bluff, California.
• California Department of Water Resources. 1996. Rice Acreage Water Management System Data for 1991-1994 for Colusa, Glenn, Yolo and Butte Counties. Red Bluff, California.
• California Department of Water Resources. 1984. Sacramento Valley Rice Irrigation Hydrology Study. For the Water Resources Control Board Contract 2-128-150-0, Central Valley Region, California.
• California Farm Bureau Federation. 1996. Backgrounder: California's Water Supply. Sacramento, California 1996.
• Glenn-Colusa Irrigation District. 1995. Report On Water Measurement Program For 1994.
• Hill, J. E. et al. 1991. Abstract to Poster of Rice Herbicide Monitoring Program.
• Hill, J. E., et al. 1992. Rice Production in California. University of California, Cooperative Extension, Division of Agriculture and Natural Resources, Publication No. 21498.
• Hill, J. E., S. R. Roberts, S. C. Scardaci, J. Tiedeman, and J. F. Williams. 1991. Rice Irrigation Systems for Tailwater Management. University of California, Cooperative Extension, Division of Agriculture and Natural Resources, Publication No. 21490.
• Hill, J. E. and S. M. Brouder. 1995. Winter Flooding of Ricelands Provides Waterfowl Habitat. California Agriculture November - December 1995, Volume 49, Number 6.
• Kreith, Marcia. 1991. Water Inputs in California Food Production. Prepared for the Water Education Foundation. Sacramento, California.
• Hill, J. E., S. R. Roberts, S. C. Scardaci, J. Young, R. E. Plant, and A. U. Eke. 1995. Rice Water Management System Adoption Trends In California, University of California, Cooperative Extension, Division of Agriculture and Natural Resources.
• University of California Cooperative Extension. 1991. Reducing Pesticide Levels from Rice Field Drain Waters of the Sacramento Valley, 1990 Progress Report.
• University of California Cooperative Extension. 1991. Rice Water Quality Demonstration Project Data.
• Williams, Jack. 1991. Draft-Rice Water Use in the Sacramento Valley; additions to Rice Water Management memo by Marlin Brandon.
• Western Ecological Services Company, Inc. (WESCO). 1991. Environmental Attributes of Rice Cultivation In California, prepared for the California Rice Commission.

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Personal Communications

• Marlin Brandon. Director & Agronomist, California Cooperative Rice Research Foundation, Inc., Biggs, CA.
• Cass Mutters. Butte County Rice Farm Advisor.
• Jack Williams. Sutter County Rice Farm Advisor.