Introduction to the Balance Sheet
Chapter 1: Land Use as it Relates to Rice Production, General Features of Rice Cultivation
The purpose of this chapter is to provide the following:
- A basis for evaluating the compatibility of rice cultivation with good environmental stewardship of the land resource that is devoted to it. To do so, some key features of the rice crop and Sacramento Valley lands where it is grown will be described.
- A general introduction to the activities involved in rice cultivation, especially for those unfamiliar with the subject.
Further details on soils, levels of productivity, and the extent of rice production will be provided in other chapters. The basis for the first chapter was Water Use for Rice Farming in California. Perception: Rice, a flooded, tropical crop, is unsuited to California (CH2M HILL, 1992).
The Unique Adaptation of Rice Culture to California's Weather, Land, and Water Conditions
Rice, the Wetland Crop
William Brewer, performing a geological survey of California, entered California's Great Valley in October 1861, just east of Livermore (Farquhar, 1949). He remarked that it was "without water during nine or ten months of the year, and practically a desert." Four months later, he reported that the Great Valley was completely flooded, with the tops of telegraph poles immersed, and that steamboats operated as far as 14 miles outside of the Sacramento River channel to rescue stranded ranchers.
Although the Sacramento Valley is known for its hot, dry summers, winter rains can be intense, and runoff and snowmelt from surrounding mountains can fill and overtop the Valley's riverbanks. Seasonal flooding has been a major feature of the region's hydrology for thousands of years. In particular, the river basins, or broad, low areas on either side of the major rivers, would flood frequently. These areas provided vast expanses of habitat for waterfowl, forming a critical link along the Pacific flyway (Frayer et al., 1989). The dependence of waterfowl and other species on wetlands and the approximately 53 percent reduction in wetland area within the U.S. during the last 100 years (Dahl, 1990) are significant reasons behind the federal "no net loss" wetlands policy. More than 86 percent of the approximately 4 million acres of wetlands in California's Central Valley in 1850 have been converted.
Historically, slow-moving floodwaters carried mostly fine sediments into the broad, flat basins adjacent to the Valley's rivers. Over time, the settling of these sediments formed the clayey soils that carpet the basins. Because water moves slowly through these soils, floodwaters on the land surface are held for a long time. The combination of floodwater from the rivers and clayey soils made parts of the basins natural wetlands.
The hydrology and soils of the basins make many land uses impossible. Strict limitations govern building within the floodplain of the rivers. Farming of upland (unflooded) crops is possible on some of the better drained soils, but impractical on many of the heavy clay soils. Many upland crops suffer drowning of roots as well as disease and fertility problems when the soil remains too wet for too long. Also, some areas in the basins tend to become alkaline when farmed under upland conditions. Flooding these soils keeps the alkalinity from developing at the land surface and reduces its impact on plants. More than half of the land on which rice is grown in California probably could not economically support other major crops. Some minor crops such as wild rice (Zizania aquatica) are also adapted to flooded conditions, but demand is currently insufficient to support their widespread cultivation. Among the major economically important crops, only rice (Oryza sativa) thrives under flooded conditions.
The location of the rice farming areas in relation to land suitability for this and other land uses is shown in Figure 1-1(University of California, Agricultural Issues Center, 1992). Note that the areas shown represent the general area where rice is grown, and also encompass many other land uses that are common to the region such as farming of other crops, some industry, domestic or urban development, roads, and canals. Because of poor drainage within these general areas, about 65 percent of the farmland is best suited to rice, and another approximately 15 percent can sustain little else besides rice. The approximately 20 percent remaining is suited equally well to other crops, but rice is sufficiently profitable to compete for this acreage.
Rice fields are continuously flooded from before or shortly after planting in April to the end of May until about 2 weeks before harvest, typically in mid-September to mid-October. Properly managed, rice cultivation is unique among the potential economic land uses in these areas because it provides many of the benefits once preserved by the natural wetland habitat that historically occurred in the Sacramento Valley.
Significant differences exist, however, between rice cultivation systems and natural wetlands. Many rice fields are flooded (160,000 acres in 1998) during the winter when many waterfowl migrate. Natural wetlands in the region are seldom flooded during the summer as rice fields are. Also, the rice field habitat is topographically and vegetatively less diverse than a natural wetland.
So, although Sacramento Valley floodwaters are now largely controlled by dams, canals, and levees, land use for rice cultivation is one way of preserving some of the historic wetlands character of the Valley's basins.
Rice, the Successful Immigrant
Rice was probably domesticated in Southeast Asia and West Africa, but the closest relatives of rice grown in California were introduced into temperate regions of East Asia about 5,000 years ago (Harlan, 1975). Temperate Eastern Asia is climatically somewhat similar to California; however, several factors make California's growing conditions more ideal for rice production than conditions in its "homelands." One indication of this is the high average crop yield in California, which is almost three times the world average (IRRI, February 1990; California Department of Food and Agriculture).
While rice generally grows well in climates that receive rainfall during the growing season, it grows even better in California's dry summers. The principal benefit of rainfall during the growing season is to supply water for plant growth. Of course, the water requirement for rice in California comes from winter precipitation that is stored as snow pack in the mountains, in surface storage reservoirs, and, to some extent, as groundwater. This provides a more reliable water supply than Asia's rainfall, so California rice crops are rarely stressed by drought. The storms and clouds that bring rainfall during the Asian growing season also temporarily block sunshine that is needed to optimize plant growth and rice production. This is not the case during California's dry summers when the many long, sunny days provide energy for rapid growth and high yields.
California has lower water temperatures and lower summer humidity than are present in many other rice-growing regions. As a result, a number of major pests and diseases are absent in California, including rice blast (Pyricularia oryzae), the most serious rice disease worldwide. Also, many of the organisms harmful to rice have never been introduced into and could not survive in California. In general, pests and diseases present in California can be controlled at levels that allow rice to take relatively full advantage of resources like water, sunshine, and plant nutrients.
California's Sacramento Valley is blessed with nearly ideal conditions for rice cultivation. During a visit to U.C. Davis in 1978, one of the world's leading rice physiologists, Shouichi Yoshida, expressed this fact when he teased California's crop scientists. Paraphrased, he said:
In California, you achieve very high rice yields and think you are very clever for doing so. I say, you have plenty of water, plenty of sunshine, relatively little disease pressure, and adequate fertility. With all of this to work with, you should be getting the highest rice yields in the world!
The total retail value or benefit of water use in rice production is estimated to be approximately $4 billion to $5 billion annually (California Rice Commission, 1990), which supports farmers, farm employees, agricultural service workers, and all sectors of the regional economy that these people affect with their earnings and taxes. The opening of international markets could reinforce the earning power of the California rice industry. In addition, the 3.2 billion pounds of rice produced can be made into 52 billion half-cup (USDA typical) servings of rice. Because people consume more rice worldwide than any other food crop, California's rice production makes a significant contribution to a hungry world.
General Description of Rice Production in California
The cropping cycle for rice is similar to that of other cereal grain crops, with some peculiarities associated with the flooded conditions under which it is grown. The prominent activities in the cycle are:
- Land preparation
- Straw disposal
- Land leveling
- Tillage and smoothing
- Levee construction and maintenance
- Pre-plant application
- Topdressing (application to the established crop)
- Initial flooding
- Flood maintenance
- Winter flooding
- Preparation and spreading of seed
- Pest control
- Animal pest monitoring and control
- Weed monitoring and control
- Grain harvest and removal
The following sections briefly describe these activities.
Harvesting removes the economically most valuable part of the rice plant, the grain. Straw is left behind on the field to decompose, burn, or to be baled and removed. Until recently, burning has been the preferred method because of its low cost and the destruction of disease-causing organisms in the straw by the heat. However, air quality concerns have resulted in a search for alternatives such as decomposition. This method is hampered by the natural resistance of rice straw to decomposition, a characteristic that helps it retain its structural integrity under flooded conditions. Straw must be put into contact with the soil and kept moist to accelerate decomposition. Baling and removal are costly relative to current returns from the sale of rice straw. Straw disposal is discussed at length in Chapter 4.
Four to six inches of water are required to suppress weeds that compete with rice. Maintenance of this water depth over thousands of acres with a minimum of floodwater requires that land be leveled precisely. This is accomplished with laser-guided earth moving equipment drawn by tractors.
Tillage and Smoothing
Most farmers till their land before planting. This consists of lifting, sometimes inverting, and pulverizing soil until a seedbed of relatively small clods covers the surface. Additionally, this surface material may be smoothed with land planing equipment, removing localized high and low spots for a more even flood. Tillage also serves to bury weed seeds scattered on the surface the previous season and to provide a surface on which the rice seeds can more easily establish themselves as seedlings.
Levee Construction and Maintenance
The flood irrigation of rice fields is controlled by a complex of channels, levees, and checks. Levees are the long mounds around and within the fields that block the free flow of water. Checks are the basins surrounded by levees, where the rice crop is grown. Weir boxes, or simply "boxes," are set into the levees to control the flow of water from channel to check, check to check, or check to channel. The boxes have a bottom and two sides, and are set into the levees with their open sides facing the levee's sides, so that they create a passageway for water. The top of the box is braced to keep the sides from falling with the weight of the levee soil piled against them. Boards are held vertically in the box across the direction of water flow. To regulate water flow through the box, the height of the weir can be adjusted by adding and removing boards of various widths.
Rice is usually fertilized before tillage is completed, so that fertilizer is mixed into the soil. Most rice fields are fertilized by granular fertilizers, along with nitrogen fertilizer in liquid or gaseous forms. Organic fertilizers, such as green manure (leguminous cover crops), are employed on some farms.
During the cropping season, the fertility status of the crop is monitored visually (e.g., yellowing can indicate insufficient nitrogen) and by sampling and laboratory analysis of plant tissue. If necessary, additional nitrogen can be applied to the flooded crop, usually in granular form.
After tillage is complete and the levees are in place, rice fields are flooded by allowing water to flow into the checks. Outflow is controlled so that, on these heavy clay soils, water soaks in, ponds, and eventually covers the field in a layer 3 to 5 inches deep.
Although rice will emerge from floodwaters, some planting systems and specific management problems require flushing, or draining and re-flooding of the planted field.
After herbicides have been applied to the rice field, the farmer must hold water in the field, or within a complex of fields, for a specified period of time. This allows the organic compounds that are the herbicides to biodegrade in the rice fields, so that water released to the drainage system is of acceptable quality for other beneficial uses. Water quality issues associated with irrigating rice are discussed in Chapter 3.
During the growing season, the flood is maintained on the field by a variety of water management systems. Only rice and a few weed species grow readily in flooded soil, so flooding is the principal weed control strategy available to rice farmers. Without it, economically (and probably environmentally) unacceptable amounts of herbicide would be required to control weeds. Nitrogen is readily retained in a flooded soil, and phosphorus availability is enhanced, so fertilizer is used more efficiently as a result of flooding.
Harvest requires that the land be drained at the end of the season, allowing the field to dry out sufficiently to accommodate traffic during harvest. At this point, the crop is nearly mature and weed growth is not generally a concern.
When straw is disposed of by decomposition, some amount of winter irrigation accelerates the process. Fields flooded during the winter, with their rich load of residual grain and native invertebrates, provide excellent habitat for migratory waterfowl. They also provide water storage volume that can be used strategically as part of the regional water management system.
In California, germinated rice seed is broadcast directly into rice field floodwaters from an airplane. It sinks, pushes its shoots above the water, and grows into a healthy rice plant. Seed must be properly prepared for planting. This entails soaking the seed in a solution of water and fungicide until the tip of the radicle, or primary root, emerges from the rice seed. At this point, the seed is heavy enough to sink in water and make essential soil contact, will complete germination rapidly, and will resist fungal pathogens during germination.
A great deal of research has been conducted by farmers, the University of California, and the agricultural chemical industry on pest control in California rice fields. A complex system of information has been generated that supports an integrated pest management approach. The idea of this approach is to understand a pest's abundance and ecological relationships well enough to guide pest management actions. Also, the most economical and/or environmentally acceptable methods of pest control are employed by preference.
For example, the effectiveness of flooding for weed control was described previously. The low cost, great benefit, and acceptable environmental impact of flooding make it the cornerstone of integrated weed pest management. Pest populations are frequently monitored as part of the program. Pest abundance is compared against critical levels (levels at which probable economic damage exceeds the cost of a pest control action). If critical levels are not exceeded, then the pest control action is not undertaken.
The advantages of the system include more profitable, environmentally acceptable farming, and reduced resistance of pests to control measures. Integrated pest management, as applied to rice in California, is documented in detail in Integrated Pest Management for Rice Farming in California, University of California Cooperative Extension, 1984.
Animal Pest Monitoring and Control
Pests of rice include vertebrates (e.g., rats, certain birds immediately before harvest), insects (e.g., rice water weevil, rice midge), and other invertebrates (e.g., tadpole shrimp). A variety of cultural (non-chemical) and chemical means are employed to control these pests when they reach critical levels of abundance.
Weed Monitoring and Control
Weed pests of rice are aquatic grasses (e.g., watergrass), broadleaved weeds (e.g., annual arrowhead), sedges (e.g., roughseeded bulrush), and algae. Cultural control is principally by tillage, proper timing and depth of flood irrigation, and achievement of a dense and competitive stand of healthy rice. Herbicides are applied to most of California's rice fields for control of grass, sedge, and broadleaved weeds.
Proper ripening is essential to the quality (flavor, texture, durability during processing) of the rice grain, which in turn greatly affects the grain's value, because it is directly consumed by humans. When rice is mature, it is harvested by combine. These harvesters either cut and thresh grain heads, or strip the grain from the heads without cutting the plants. The grain is then delivered by auger to a bankout wagon or truck in the field. Trucks remove grain from the field for processing.
The following sections present the justification for ratings of the rice industry's performance relative to the environmental value of land use.
Straw recycling is on the increase, either in the field by decomposition, or by removal for recycling into fiber products or as energy. Recovery of economic or environmental value from straw while reducing burning emissions increases the environmental value of land use.
Tillage of rice and other crop lands increases the susceptibility of soil to some wind erosion. However, wind erosion is not considered a major problem in the region, and tillage is similar for land used for cultivation of rice and many other crops.
Irrigation of crops typically causes some soil erosion. However, in the case of rice, this effect is minimized by the slow rate of water flow along a level land surface between checks and levees. Summer flooding also improves the wetland value of rice fields. Flood irrigation of rice fields is a stable, established practice, and requires levels of investment similar to irrigation of other crops.
Winter flooding occurred in the low-lying areas of the Sacramento Valley before dams were placed on the major rivers feeding the area. By emulating this wetland condition, winter flooding of rice fields greatly increases the wetlands value of rice fields. Since 1991, winter flooding has increased from about one-tenth to over 40 percent of rice lands. Rice farmers and their collaborators have worked to make this practice a success.
Residual materials from rice harvest directly benefit the environment by providing feed and habitat for wildlife (see Chapter 6).These benefits are increasing as a result of rice industry investment, although the advent of more efficient harvesting technology offsets some of this habitat benefit. Harvest produces the economic product of rice farming: rough or "paddy" rice. Yields in California rice fields surpass all other large-scale, single-crop-per-year, rice growing regions worldwide. Furthermore, most of California's rice farmland is unsuitable for other crops. Therefore, relative to most alternative land uses, rice farming is economically productive and sustainable. One indication of this is the long-term growth and stability of the rice industry in the region, where it is a mainstay of the local economy. Using land for rice farming benefits people, and helps provide the economic resources they need to be good environmental stewards of their land.
California Agricultural Statistics Service. 1990.
California Department of Food and Agriculture. 1992.California Field Crop Statistics for 1991. Sacramento, California.
California Rice Promotion Board. 1990. California Rice Industry Economic White Paper. Yuba City, California. 1990.
Dahl, T. E. 1990. Wetlands Losses in the United States 1780's to 1980's. U.S. Department of the Interior, Fish and Wildlife Service. Washington, D.C.
Farquhar, F. P. (ed.). 1949. Up and Down California in 1860 - 1864: The Journal of William H. Brewer. University of California Press. Berkeley, California.
Frayer, W. E., D. D. Peters, and H. R. Pywell. 1989. Wetlands of the California Central Valley: Status and Trends - 1939 to Mid-1980's. U.S. Fish and Wildlife Service. Region 1, Portland, Oregon. Harlan, J. R. 1975.Crops and Man. American Society of Agronomy. Madison, Wisconsin.
International Rice Research Institute (IRRI). 1990. IRRI Rice Facts. Revised February.
University of California, Agricultural Issues Center. 1992.Maintaining the Competitive Edge in California's Rice Industry.