Yet government leaders in nearly every country allow land that could produce grain to be paved over or degraded by erosion. But with a decade of faltering yields behind us, this is risky policy. In the United States, net losses of cropland between 1982 and 1992 covered an area the size of New Jersey. Erosion and retirement of marginal lands have pulled more than 24 percent of Kazakstan's grainland from production since the mid-1980s. Yields are no longer rising fast enough to offset the steady loss of grainland, nor to adequately feed nearly 90 million new people each year.
Urbanization is appropriating cropland nearly everywhere cities are growing.
And because many cities started on good farmland, the spread of roads, buildings, and industrial parks inevitably eats up some of the most productive remaining land. In the most crowded regions, especially Asia, such losses cannot be replaced, because little room for cropland expansion exists. As urban populations swell from less than 50 percent of world population to more than 60 percent in the next 30 years, the problem will become more acute. More than one third of this land was prime farmland. Depletion or diversion of irrigation water .