Calag Archive

Not available – first paragraph follows: Salinity and drainage problems have plagued agriculture in California from the time irrigation was introduced in the second half of the nineteenth century. The emergence and spread of such problems, and the variety of ways in which irrigators and public agencies have responded to them, may be traced in the histories of the Imperial and San Joaquin valleys.

Not available – first paragraph follows: It has been said that the Colorado River is the most litigated, regulated, and argued-over major river in the world. The river provides irrigation water to 1.5 million acres within the seven states of Colorado, New Mexico, Utah, and Wyoming (Upper Basin) and Arizona, California, and Nevada (Lower Basin). More than half of this acreage is in California. The river also furnishes a full or supplemental supply of municipal and industrial water to 17 million people. The Republic of Mexico receives water from the river to irrigate 0.5 million acres of farmland and supply 0.5 million inhabitants.

Not available – first paragraph follows: Saline and sodic soils occur naturally in arid and semiarid regions, and as water development brings more land into irrigation, the salinity problem expands. The condition is aggravated by poor soil drainage, improper irrigation methods, poor water quality, insufficient water supply for adequate leaching, and insufficient disposal sites for water that leaches salts from the soil. Problems caused by soil salinity are compounded when a high water table impedes root development and concentrates salts in the already limited root zone.

Not available – first paragraph follows: The huge trough known as the Central Valley of California is enclosed on the east by the gently rising slopes of the tilted igneous Sierra Nevada and on the west by the strongly folded and faulted Coast Range of more recent sedimentary formations. At one time, the trough was an arm of the sea and marine sediments dominated the deposits. In these sediments is contained a body of unsuitable saline entrapped water.

Not available – first paragraph follows: When water is applied, particles of soils with high smectite (montmorillonite) clay content may swell considerably due to hydration of expandable soil minerals. Such swelling reduces the cross-sectional area of soil pores. The process of swelling is more pronounced in the presence of high sodium or low salt concentrations, or both, in the soil water.

Not available – first paragraph follows: The Salton Basin extends 200 miles from San Gorgonio Pass in the north through the Coachella, Imperial, and Mexicali valleys to the Gulf of California. The basin covers a drainage area of about 8,000 square miles and at its deepest point is 273 feet below sea level — about the same as Death Valley.

Not available – first paragraph follows: Most of the San Joaquin Valley has been farmed in one fashion or another for more than a hundred years The Valley trough was generally dry-farmed until deep-well turbine pumps were developed in the 1930s and 1940s and irrigation became common. Even though much of the land was in production, it was not irrigated every year: there was some pattern of rotation, such as dry-farming for one year, irrigation for two, and fallow for one. Now, almost 5 million acres of agricultural land on the Valley floor are irrigated.

Not available – first paragraph follows: Plants may be categorized as ha-lophytes or glycophytes, as far as their responses to salinity are concerned. The distinction is not absolute, because species range from highly tolerant to very sensitive.

Not available – first paragraph follows: One strategy available to farmers with saline soils is to select salt-tolerant crops. Crop tolerance to salinity ranges widely from the very salt-sensitive bean to the highly tolerant barley and cotton.

Not available – first paragraph follows: A biological system under stress probably uses more energy than the same system in the absence of stress. When a plant is exposed to high levels of salt, extra metabolic energy is likely to be consumed in processes related to osmotic adjustment within the cells. Without this adjustment, the plant would lose water to the surrounding saline environment, dehydrate, and die.

Not available – first paragraph follows: Root rots caused by species of Phytophthora are economically important diseases affecting a wide range of agricultural and ornamental crops. Although diseases caused by these fungi can sometimes be suppressed by fungicide treatments or use of resistant cultivare, in many situations they cannot be effectively controlled. These difficulties have prompted considerable research into conditions favoring the survival, reproduction, and spread of Phytophthora spp. in soil and their infection of plant roots.

Not available – first paragraph follows: Salt stress inhibits growth throughout the plant life cycle, but seed germination is generally the most sensitive stage. Salt stress mimics water stress in many ways, leading to the suggestion that the principal effect of salt is osmotic. However, since some salts are more inhibitory than others, specific toxic effects must also be involved. Although sodium chloride is among the less toxic salts, it is one of the most common and thus one of the most troublesome to agriculture.

Not available – first paragraph follows: More than 40 million of California's 100 million acres are rangelands. The forest, grassland, and rangeland environments comprise about two-thirds of the land area of the state, and more than 50 million acres are grazed. The desert saltbush, an abundant, shrubby inhabitant of some of California's driest, saltiest rangelands, is one of many salt-tolerant shrubs, trees, and grasses that have become increasingly valuable as resources for arid and saline lands. These salt-tolerant plants (halophytes) provide forage for livestock and wildlife in range-lands throughout the West. Furthermore, many have been shown to be adaptable to genetic manipulation by selection or breeding.

Not available – first paragraph follows: Despite their salinity, tidal marshes are highly productive. Salt marsh plants are often reported to have rates of productivity exceeding those of many cultivated species. Although little used today, some halophytes have been exploited historically as a food source for humans or domestic animals. Many of these or related species are found in California, such as eelgrass (Zostera marina), salt grass (Distichlis spicata), and cord grass (Spartina alternifolia).

Not available – first paragraph follows: California's native mesquite grows primarily in areas of shallow ground water where temperatures are rarely below 24°F. Many of these areas have naturally occurring saline surface or subsurface soils — up to 88 dS/m (about 56,300 mg/L) in the saturation extract. Root systems of mesquite, including the native species, Prosopis glandulosa var. torreyana, are well adapted for growth in areas where the plant must rely primarily on ground water. Another species, Prosopis tama-rugo, native to the Atacama Desert of Chile, where average annual rainfall is less than Vi inch, relies wholly on groundwater derived from snow and rain in the Andes Mountains.

Not available – first paragraph follows: All waters and soils contain salt. Even nonsaline irrigation waters like those of the Sacramento-San Joaquin Delta contain enough salt to create a hazard if drainage is insufficient. Delta channel waters typically have an electrical conductivity of about 0.2 dS/m (about 128 mg/L salt) and contain 350 pounds of salt per acre-foot of water. With adequate subsurface drainage and an average annual rainfall of 15 inches, however, neither salinity nor a shallow water table is a problem.

Not available – first paragraph follows: Some crops, such as cotton, barley, safflower, or sugarbeet, can be grown in relatively saline soils; others, including beans and corn, can be grown only in nonsaline soils. It is intriguing to speculate that a sensitive crop plant might be genetically altered to withstand high salinities. Breeders have considered this approach for many years, but research along these lines has been neglected in favor of other problems. Instead, management options have been used to alleviate saline conditions and, during reclamation of salt-affected soils, farmers have limited their choice of crops to the more tolerant species.

Not available – first paragraph follows: Although boron is an essential plant nutrient, it becomes toxic to growing plants if excessive levels are present in the root zone. Soils containing high native concentrations of boron occur primarily in arid and semiarid environments where drainage or leaching, or both, are restricted. Soils periodically exposed to water containing appreciable amounts of boron, including groundwater and irrigation water, may also develop elevated levels of the element.

Not available – first paragraph follows: Molecular techniques such as recombinant DNA technology may ultimately have their most significant effect on agriculture. Recent advances raise the possibility of the development of new plant germplasm through the introduction of any gene from any organism into plants. Several leading laboratories have achieved the transfer and expression of bacterial and foreign plant genes in plant cells. Increasing attention is now being paid to the use of recombinant DNA technology to isolate and transfer genes governing agriculturally important characteristics such as salinity and drought resistance.

Not available – first paragraph follows: Manipulation of the plant's environment to reduce salinity will continue to be the principal management strategy in the future. Competition for limited quantities of high-quality water, however, may eventually force growers to use lower quality water, such as municipal and irrigation return flows. Development of new, more salt-tolerant crops and crop varieties will therefore provide an important supplemental means of managing salinity.

Not available – first paragraph follows: Most soil salinity problems in the San Joaquin Valley are directly related to shallow saline water tables. Where no such water tables exist, soil salinity problems usually do not occur, because irrigation water used in the Valley is generally very low in salts.

Not available – first paragraph follows: Expansion of irrigated agriculture would contribute significantly toward meeting world food and fiber needs but, at the same time, would run headlong into competition for ever more limited water supplies. By reassessing the criteria for suitability of water (and land) for irrigation, however, available supplies can be expanded significantly. Very conservative standards have been used in the past. If these standards are relaxed, water generally classified as too saline for irrigation can often be used successfully without hazardous long-term consequences to crops or soils, even under conventional farming practices. Adoption of new crop and water management strategies would further facilitate the use of saline waters for irrigation and could make possible a sizable expansion of irrigated agriculture.

Not available – first paragraph follows: Historically, legislation concerning groundwater has been slow to develop. As a result, from a legal and institutional perspective, drainage and groundwater salinity problems today are addressed only in part.

Not available – first paragraph follows: With future water supplies for agriculture likely to be increasingly limited, it is important to consider direct use of water of impaired quality — increasing use and resue over time of water with varying levels of total dissolved solids. Plant breeding will provide some salt-tolerant varieties that can produce yields nearly equivalent to those of crops traditionally produced in areas without salinity problems. Harmful physical and economic effects may thus be lessened, but farms in areas unaffected by salt buildup may still be able to produce better quality products at lower cost than those in salt-affected areas.