After comparing possible additions to the world's wheat-growing area and the likely increase in the number of bread eaters, Crookes estimated that only three decades remained before all available wheat acreage would have to be under cultivation to meet current needs. He was particularly concerned that the easy expansion of U.S. cropland, by 230 percent between 1870 and 1888, was drawing to a close. He emphasized the potential for yield improvements through increased application of fertilizer, particularly nitrogen. His optimism was based, not on existing technologies, but on the commercial potential of fixing atmospheric nitrogen and using it to produce chemical fertilizers-a technology that was still in the future. Proposing the use

Following World War II, there again was concern about food and land supplies. This postwar interest was accented by the creation of the Food and Agricultural Organization (F AO), which signified recognition of a potentially major problem. Nutrition goals, staggering projections of population growth, and the information system of F AO made many more people aware of the potential problem of inadequate agricultural land. Almost simultaneously, Americans and others were made aware of limits on supplies of natural resources. The period was a high point in the U.S. public's concern over conservation of these resources. Vogt suggested that mismanagement of land and water resources was proceeding at such a rate that even ongoing levels of food production might be threatened.4 In addition, birth rates in the United States increased sharply, while land was being lost through erosion. So great was the concern that a national effort was undertaken, with each state enlisted to determine the techniques that might be adopted and the level to which food production could be raised by 1985. However, the potential of new technology was so great that by the late 1970s these estimates were far surpassed and the United States could meet its domestic demands with much less land and a much larger margin for exports.5