Spring, 1991 (v3n3)
	Drought & Sustainability by Dave Chaney & Chuck Ingels, SAREP The current drought, possibly more than any other issue this century, raises serious questions about the sustainability of California agriculture. Concerns about economic viability, food safety, groundwater contamination, and farm labor health and safety have motivated both researchers and farmers to develop more environmentally sound, resource-enhancing production systems. But none of these can match the implications, anxiety and urgency of a severe drought. Surface water supplies are the hardest hit and farmers in many irrigation districts are already feeling the pinch. Growers in some locations will receive 25 percent or less of their normal deliveries. The ramifications of these restrictions depend on the crop grown and on whether other sources of water are available. It is likely that in some areas, the acreage planted to field and vegetable crops will be drastically reduced. Already established orchards and vineyards require a certain amount of water to stay alive, but the chances of actually harvesting tree or vine crops will depend on growers being able to locate other sources of water. Groundwater is the major alternative to decreasing surface supplies, but drilling a well can be very costly and take up to six weeks or more. Furthermore, as farmers increase groundwater pumping or drill additional wells the depth to groundwater gradually increases. This adds to the expense of drilling a well and compounds the groundwater overdraft problem. (Overdraft occurs when more groundwater is pumped than is replaced each year by percolation.) Among the side effects of overdrafts are the increased cost of pumping water and declining water quality. Another reason the drought is a focal point for agricultural sustainability is the increasing tension between urban/industrial demands for water and agriculture. An indicator of this can be seen in estimates for changes in water use between the years 1985 and 2010 (Table 1). Overall, the demand for water is expected to increase by 4.2 percent during this period, largely in the urban sector. Table 1. Net Water Use in California, 1985-2010 Sector 1985 2010 % Change millions of acre feet Agriculture 27.7 27.4 -0.1 Urban 5.6 7.2 +28.9 Wildlife, Energy, Recreation 0.9 1.0 +10.0 Total 34.2 35.6 4.2 Source: California Dept. of Water Resources Bulletin 160-87 Population growth in California will significantly increase municipal and industrial demands. In contrast, net water use in agriculture is estimated to decline slightly. This is based on the assumption that California agriculture may become somewhat less competitive in national and international markets. Water officials estimate that the demand in the year 2010 will outstrip supply by about 2.1 million acre feet. In a serious drought situation this deficit would be even greater. The prospect of a very long-term drought compounds the problem even further. Historical data shows that we are faced with the distinct possibility of continued below average rainfall. In 1980 the California Department of Water Resources funded a study by the University of Arizona's Laboratory of Tree-Ring Research that showed a 50-year drought during the late 1700s and early 1800s (Figure 1). Figure 1. Long Term Reconstructed California Precipitation not available Precipitation was lower in each of these years than during the dry seven-year span from 1928 through 1934 which the DWR uses for planning projects with sufficient capacity to furnish a reliable water supply. Thus, California's water planning may be based on relatively optimistic estimates of drought conditions. (Association of California Water Agencies, 1989) Another long dry period identified in the tree ring study included a 20-year period between 1865 and 1885, which wiped out the cattle industry in Southern California. Even if average or high rainfall years punctuate long drought periods, the basic problem remains: How to meet the water demands of agriculture and a growing population with limited supplies. Water Wise Farmers What can farmers and ranchers do to make the most of limited water supplies and increase the stability of their farming systems during drought periods? Based on recommendations by University of California researchers, there are several key points that apply to all farmers and ranchers. These include: Improve the receptivity of rainfall catchment areas. Enhance soil water infiltration and soil water holding capacity by increasing soil organic matter. Match water applications closely to crop needs. Improve the efficiency of irrigation systems. Reduce evapotranspiration with windbreaks. Try to begin the season with a full profile of soil water. Control weeds that could compete with the crop for valuable soil moisture. Field, Vegetable Crops In conjunction with the principles outlined above, there are three additional recommendations that apply specifically to annual cropping systems. Plan ahead. Determine what your water supply will be and then decide the acres that can be effectively irrigated with that amount of water. Use your best land for limited plantings. Crop selection and rotation. Select crops and growing seasons which use less water. Winter grains, for example, use significantly less water than summer field and vegetable crops. If you plant during the summer, choose short season crops and varieties. Know the critical stress periods for your crops. Table 2 provides that information for several field and vegetable crops. It is particularly important to avoid drought stress during these developmental stages. Tree Crops "Tree growers have more potential to minimize adverse effects of deficit irrigation on crop production than do field and row crop growers. This is due mostly to the greater separation between the vegetative and reproductive growth stages in trees." This is according to a document entitled Irrigation Management for Fruit and Nut Trees Under 1991 Drought Conditions, which is available through most farm advisor offices. The author is Dave Goldhamer, extension specialist at Kearney Agricultural Center, who has performed numerous water stress experiments on other nut and tree crops. Goldhamer also wrote a more extensive 1989 UC publication, Drought Irrigation Strategies for Deciduous Orchards. There are specific periods in the growing season during which applied water can be reduced or withheld from tree crops without significant yield losses, according to Goldhamer. At other times, deficit irrigation can result in substantial loss in yields in either the current season, the following season, or both. These critical periods vary with each tree species, and the 1991 report suggests general strategies based on tree species. In general, the drought-sensitive growth stages are early season (bud break through fruit set), fruit growth and development, and postharvest. Table 2. Critical Growth Periods to Avoid Drought Stress for Field and Vegetable Crops. CROP CRITICAL PERIOD Alfalfa Just after cutting for hay and at the start of flowering. Small grains During crown root development and from heading to anthesis. Beans/Peas Flowering, pod setting period, and ripening. Corn/Sorghum During crown root development and at pollination. Cotton During early canopy development. Mild stress desirable during early boll growth. Sugar beets During canopy development. Sunflower Flowering and seed development stages. Brassicas During head formation and enlargement. Lettuce Just before harvest. Potatoes After formation of tubers, from bloom to harvest. Radish During the period of root enlargement. Tomatoes Flower formation and fruit enlargement. Strawberries Fruit development to ripening. Melons From blossom to harvest. Source: Drought Tips for Vegetable and Field Crop Production. UC Agriculture and Natural Resources Leaflet No. 21466. Early season. Early spring growth is needed to establish the fruiting wood for the following year's crop. It is therefore essential to supply adequate water early in the season; this is done by starting the season with a nearly full soil water profile. Fruit Growth and Development. Adequate water is required during the rapid growth of fruits which exhibit a "double sigmoid fruit development pattern," but stress can be imposed during the "lag (stage 2) phase of growth." Generally, nut growth is less sensitive to water stress than fruit growth, but other yield and quality components may be affected. Postharvest. With the exceptions of almond and apricot, "the period after harvest is generally most water stress tolerant." Other considerations in a drought year include good irrigation scheduling and proper irrigation system design, according to Goldhamer. Also, young trees should be fully irrigated since the goal is to maximize vegetative growth to bring trees into bearing early. Finally, some growers may be considering very severe pruning in order to simply keep their trees alive. This will greatly reduce water use, but only at the expense of production for several years. An even more drastic step would be to cut off all scaffold branches at waist level, a practice known as "dehorning." Goldhamer advises using this measure only if eight acre-inches or less water are available for the season. This drastic step would probably not be needed on pistachio or walnut, and trees of some species, such as almond, may never recover to their full size. Almond Research. Critical information has recently been developed on managing almonds with deficit irrigation. Terry Prichard, water management specialist in Stockton recently reported on first year results of a four-year irrigation study. In this experiment, yield was not affected by up to 50 percent deficit irrigation, although the number of stick-tight hulls at harvest increased significantly. Similarly, in the first year of an irrigation cutoff study performed by Goldhamer, hull-splitting was reduced as the length of the preharvest water cutoff interval in-creased. Yields of all cutoff treatments were similar, even alter two years. However, withholding the postharvest irrigation resulted in significantly lower yields in all the cutoff treatments in the second year. Range, Pasture The following tips are from an article by Plumas-Sierra counties farm advisor Holly George (March 1991 newsletter): Roots transport moisture and nutrients to growing plants. When plants are overgrazed, root growth stops; when root growth stops, leaf growth stops too. Irrigated pasture management practices which encourage root and leaf growth are the same practices which allow plants to make the best use of soil moisture. They include: rotation grazing with adequate rest and regrowth periods leaving 4-6 inches of top growth at the end of each grazing period fertilizing properly applying irrigation water in the right amount at the right time. Range and dry pasture forage production depends entirely on natural moisture. Overgrazing during a drought does more damage to perennial plants than during a season of normal moisture. It reduces plant vigor, stops root and leaf growth, reduces ground cover, and invites accelerated erosion. Once erosion begins, it tends to get worse each year, further reducing plant vigor and forage production. This process is difficult to reverse. Rather than risk permanent damage to grazing resources: reduce livestock numbers to balance with forage supply cull herds more than normal sell calves and lambs early determine forage needs and buy needed supplements early grow small grains or sorghums for hay or pasture (these need less water than conventional forage crops) defer planting perennial pasture, hay, or range seedings until a year with more favorable water outlook keep spring developments, stock tanks, float valves, and pipelines in good working order so water is not wasted cover troughs and tanks to reduce evaporation prepare for hauling stock water give spring development high priority (even mediocre springs will be helpful) consider herding or other livestock distribution methods to make use of under-used areas don't overgraze or otherwise disturb streambank vegetation (it will be needed to prevent erosion, reduce sediment, and provide food and cover for wildlife) well-established seedlings can tolerate heavy use better than native range. Wildlife will suffer during a drought as much or more than domestic livestock. The wildlife that shares your land is a valuable natural resource. To help wildlife: include additional features at stock water developments which will allow small animals and birds safe access to water (these are usually not expensive and are easily installed) fence ponds and springs and install collector pipes to deliver water to a tank or trough. This will save the water source from damage by livestock trampling, as well as allow access by small animals and birds to lush vegetation that grows close to wet areas. For more information concerning your crop, and soil and water conditions, contact your local Cooperative Extension office and/or the Soil Conservation Service office. References Association of California Water Agencies. 1989. Coping With Future Water Shortages: Lessons From California's Drought. Bowers, Wilbur 0., Richard L. Snyder, Susan B. Southerd and Brenda J. Lanini. 1989. Water-Holding Characteristics of California Soils. UC ANR Publication No. 21463. California Dept. of Water Resources. 1987. California Water: Looking to the Future. Bulletin 160-87. Coppock, Raymond. 1984. California's Groundwater Resource. UC ANR Leaflet No. 21393. Fritts, H.C. and G.A. Gordon. 1980. Annual Precipitation for California Since 1600 Reconstructed From Western North American Tree Rings. California Dept. of Water Resources Agreement No. B53367. George, Holly. March 1991. Agriculture and Natural Resources, Cooperative Extension newsletter, Plumas-Sierra counties. Goldhamer, David A. and Richard L. Snyder (eds.). 1989. Irrigation Scheduling: A Guide for Efficient On-Farm Water Management. UC ANR Publication No. 21454. Goldhamer, David A. 1989. Drought Irrigation Strategies for Deciduous Orchards. UC ANR Publication No. 21453. Goldhamer, David A. 1991. Irrigation Management for Fruit and Nut Trees Under 1991 Drought Conditions. Hanson, Blaine and Warren Bendixen. 1991. Improving Irrigation Water Management. University of California Irrigation Program, UC Davis Dept. of Land, Air, and Water Resources. Prichard, Terry. 1988. Agricultural Water Management in a Dry Year. Snyder, Richard L., Stephen T. Grattan, and Larry Schwankl. 1989. Drought Tips for Vegetable and Field Crop Production. UC ANR Leaflet No. 21466. [ Back | Search | Feedback ]