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The level of future agricultural production in Central Arizona depends upon the availability of land and water, the cost of water, and opportunities to grow crops yielding high returns per acre-foot of water. Suitable land is abundantly available but groundwater appurtenant to these lands is becoming increasingly costly. Opportunities to grow high-value crops are subject to the vagaries of commodity markets and government programs. This study estimates the direction and magnitude of expected agricultural adjustments in response to a declining land and water base, increasing water costs, and intra-county transfer of cotton allotments. The study region, encompassing all areas of Maricopa County relying solely or primarily upon groundwater for irrigation, is divided into two water resource areas. Area A has low-cost, poor quality water and only cotton for a high-value crop. Area B has highcost, good quality water and cotton, vegetables, and citrus for highvalue crops. Nine representative farm models are developed characterizing the structure of the agricultural sector of the economy in these two areas. Data for ten crops grown by these nine farm size groups are incorporated into linear programming models to make projections for 18 water situations distinguished on the basis of source, availability, and cost of water. Projections are made for the period 1967 to 2015. Projected adjustments show over 20 percent declines in land and water use and a 13 percent decline in net revenues over variable costs of production for the study region by 2015. These declines occur due to a loss of 68,000 acres of land to urban uses, and the abandonment of lowvalue crops made unprofitable by rising water costs. Declines in resource use and incomes are mitigated by a 10,000 acre increase in cotton production due to transfers of allotments from an adjacent region experiencing greater losses of land and water to urban uses. Projections by water resource area and water situation show 7 and 13 percent decreases in land and water use and a 7 percent increase in net revenues over variable costs for Area A. This divergent movement of resource use and revenues occurs because a 64 percent increase in cotton acreage offsets substantial reductions in sorghum and safflower acreages. Area B projections show approximately a 30 percent reduction in land and water use and a 23 percent reduction in net revenues over variable production costs. These reductions occur because all resources lost to urban uses come from this area and large acreages of low-value crops go out of production due to rising water costs. Only small acreages of short staple cotton allotments are transferred to Area B farms because Area A farmers can afford to pay more for surplus allotments. Area B experiences a net loss of cotton acreage because long staple allotments are transferred to Area A ferns when water costs make this variety of cotton unprofitable in Area B water situations. Projections by water situation within the two water resource areas vary from increases in resource use and net incomes to large decreases. The agricultural sector of Maricopa County expands until 1960, then enters a stage of decline, accelerated by large losses of land and water resources to urban uses in one irrigation district with adequate supplies of low-cost water. A comprehensive land use plan with zoning restrictions preventing urbanization of low-cost water areas would help maintain agricultural resource use and incomes at levels higher than will otherwise occur. Such a plan would also help maintain the quality of Che urban environment in Maricopa County.

The actual evapotranspiration rate for wheat at the Campus Agriculture Center (CAC) and alfalfa at the Maricopa Agricultural Center (MAC) were measured using the Bowen ratio technique for near real-time irrigation scheduling. The Bowen ratio method underestimated evapotranspiration when compared with AZMET and Penman data. There were problems with the hygrometer and the net radiometer which might have caused this underestimation. The height-fetch ratio requirement was not met, and this may have affected the data. Irrigation scheduling programs and the technique to schedule irrigation in a near real-time were developed. Irrigation programs were not field tested because of the problem with field data. Simulated data was successfully used to demonstrate its application. It was found that irrigation could be scheduled in a near real-time with the programs provided reliable data and proper data acquisition systems are used.

This item was digitized as part of the Million Books Project led by Carnegie Mellon University and supported by grants from the National Science Foundation (NSF). Cornell University coordinated the participation of land-grant and agricultural libraries in providing historical agricultural information for the digitization project; the University of Arizona Libraries, the College of Agriculture and Life Sciences, and the Office of Arid Lands Studies collaborated in the selection and provision of material for the digitization project.

Cover title: Draft technical appendix. / Phoenix Urban Study: Final Report / The work upon which this publication is based was supported by funds provided by the U.S. Army Corps of Engineers, Los Angeles District, as authorized by resolution of the Senate Public Works Committee on July 31, 1973. This report was prepared as a contribution to the Phoenix Urban Study under auspices of the U.S. Army Engineer District, Los Angeles.

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