A production function relating irrigated crop yield to the quality and supply of irrigation water is developed. It was found that the adverse effects of saline irrigation water can be offset by application of additional water over and above that required for plant transpiration. Results indicate that a degradation of the water supply in the Colorado River at Imperial Dam from the existing level of electroconductivity of 1.50 mmho to the projected level for the year 2000 of 2.0 mmho would cause a decline in the return to land and water of about 14% for farmers in the Imperial Valley of California. Because of the relatively elastic demand for irrigation water at the current price, any attempt to ration water through a market price mechanism would have no effect, unless water rates were about double their current levels.
The research area lies within the lower Pajaro Valley and is that part of the Pajaro Soil Conservation District lying within the boundaries of Santa Cruz County, California (fig. 1). A large part of the 32,500 acres of Santa Cruz County cropland lies within this district. The development of agriculture in Santa Cruz County began about a century ago. Apples, still the most important single crop, were introduced in 1852 reaching their maximum expansion of about 12,000 acres in 1930.
P ROPOSALS for programs or policies that would "do something for agriculture faced with urban pressures" are nearly as numerous as the proverbial fleas on a hound dog. Their origin, using the sometimes questionable benefit of an educated hindsight, might conceivably be traced to the early urban-rural fringe areas of antiquity-the Nile Valley, Mesopotamia, and the Indus River. Urban developments have occurredand taken land from fanning-wherever agricultural production, itself dependent upon a moderate climate, has stimulated marketing and trade activities as well as population growth and concentration. Conversion of land from agricultural to nonagricultural use is a normal aspect of economic growth.The historic abundance of natural resources available for man's use has been largely responsible for an almost congenital lack of concern for these resources by their users. California, long considered a state with limitless land and water resources, has only very recently awakened to the fact that a population explosion and attendant urbanization may be posing a serious threat to the stability of its economically important agricultural sector.During the decade of the 1920's, concern developed over both actual and potential water shortages. Eventually-after at times violent debate and study-plans were developed and are being put into effect to develop California water resources with a maximum of social and economic product and a minimum of economic cost and social waste. Although not all water-oriented resource problems are solved as yet, at least effective progress is being made for the long-run conservation use of this limited resource in an urbanizing economy characterized by a strong irrigationbased agricultural sector.Concern over land resources has been slower to develop. Interest in greenbelts, open space, loss of agricultural land, and conservation of prime agricultural land is a recent development [11]. It is only in the postwar era that serious land-use competition problems have emerged requiring that major attention be directed to land resources. The particular combination of natural conditions that first stimulated a highly specialized agriculture has also attracted and stimulated a rapidly expanding urban population. This in tum has begun to compete with agriculture-and fre- • Giannini Foundation Paper No. 271.
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