Spatial variation of in situ available water content was studied along with related parameters over three 16-ha irrigated fields. The fields, two near Marana (Pima County, Arizona) and one near Casa Grande (Pillai County), range in texture from very fine loam to loamy sand. All soil series present are mapped as Entisols or Aridisols. A 50-m grid provided 56 sampling sites in each field. Each site was sampled at 30, 60, 90, 120 and 150 cm. Samples were collected from each field following a heavy irrigation in March 1977. Bulk samples were collected two days and four weeks after the application of approximately 300 mm of water, to determine in situ water content at field capacity and moisture redistribution with time. Related parameters such as particle size distribution and soil water characteristics were also studied. Bulk density and saturated hydraulic conductivity were determined from undisturbed, core samples. The measured parameters showed different patterns of variation within the same field as well as from one field to the other. Spatial variability of saturated hydraulic conductivity was the highest for which coefficient of variability (CV) ranged upward to 108%. Bulk density, on the other hand, showed the lowest coefficient of variability, as low as 5%. The in situ available water content (AWC), estimated by subtracting moisture content at 15 bars from the corresponding in situ FC values, showed a general tendency to increase with depth corresponding to the increase in percent silt plus sand with depth in all three fields. The coefficient of correlation between the two parameters was high (up to 0.70). The mean values of AWC as estimated using 0.1 bar values for field capacity in the laboratory were consistently higher than the in situ values. The values were within 25 - 35% of each other in Fields 1 and 2, while in the sandier soil of Field 3, the AWC was overestimated by an average of 74% in the laboratory. The CV showed an irregular tendency to increase with depth, but was consistently high in the 150 cm layer in all three fields. Values estimated in the laboratory showed lower CV and higher correlations with soil separates than in situ AWC in all three fields. These two observations can be attributed to the elimination of in situ factors such as texture stratification, compaction, and/or amount of water applied. Agricultural soil formed on water transported material at 0.1 bar were highly correlated with sand (r = -0.8) and the 15 bar values were better correlated with clay (r = 0.5). Also, the coefficient of variability increased consistently with decreases in moisture content. The analysis of variance showed the three fields to be heterogeneous. The variation for within and between the 5 depth groups was significant. A two-way interaction between depths and subareas within each field accounted for 44, 45 and 38% of the total variability in Fields 1, 2, and 3 respectively. Cumulative frequency distribution plots, full normal plots, Kolmogorov-Smirnov tests of goodness-of-fit, tests of skewness and tests of kurtosis were conducted to test the null hypothesis of normal distribution for each parameter. The full normal plots, being sensitive to deviations from normality, rejected the null hypothesis in all cases with few exceptions. They showed the data tends to be skewed to the right and/or kurtic. The alternative frequency distribution of the parameters indicated the data to be asymmetric, short tailed with the exception of percent sand which was symmetric, short tailed for all three fields. A power transformation is suggested as a possibility for transforming the data to get near normal distribution.

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.