Driving north from Wichita, Kansas, toward Salina on a warm day last October, I saw an oil-well pump sitting in the middle of a sorghum field. And not just one. As I drove, I saw hundreds more, maybe thousands, all surrounded by amber waves of grain. Like giant, insatiable gulls, they bobbed their heads up and down, up and down, gulping black crude from the earth’s depths. Oil wells in farm fields. Here was a symbol for modern agriculture, dependent on petroleum-based fertilizer to produce high yields.