alfalfa acreage is converted to corn, but increase if cotton or sorghum is converted (R.Allen, Univ. of Idaho, written commun., July 12, 2007. Data from Durwood et al. [1960]).

Given the regional differences in rainfall and groundwater storage, the feasibility and sustainability of biofuel crop production as a function of water availability may vary significantly by region. Figure 2-2 shows the state-by-state water requirement of irrigated corn in the continental United States. It demonstrates that the amount of rainfall and other hydroclimate conditions in a given area causes significant (10-fold) variations in the water requirement for the same crop. Clearly there will be geographic limits on certain kinds of biofuels feedstock simply based on their water require-

FIGURE 2-2 State-by-state water requirements in 2003 of irrigated corn (gallons of irrigation water per bushel).

SOURCE: N.Gollehon, USDA ERS, written commun., July 12, 2007. Based on data from 2003 Farm and Ranch Irrigation Survey (USDA, 2003).

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