E ver since the first organized harvests of prehistory, the plow has defined the universal symbol of agriculture. So how radical is it that America's farms are gradually abandoning the plow as a no-till revolution slowly sweeps across the American heartland? Perhaps more than any emerging green technology, this little noticed, ongoing shift in the business of farming may hold the key to feeding humanity in a post-petroleum world. Agriculture has evolved through several so-called revolutions since some long-forgotten farmer hooked a digging stick up to a cow and invented the plow, one of the most enduring and widely adopted inventions of all time. The most recent and well known agricultural revolution, the Green Revolution of the 1960s, is widely regarded as enabling modern agriculture to keep up with global population growth through more than doubled yields of hybrid crops that thrive on fertilizer-intensive farming. But slowly over the past several decades, American agriculture has been undergoing another fundamental transformation as farmers increasingly adopt the once-heretical practice of no-till farming. Why am I, a geologist, excited about this recent development in farming practices? Plowing the soil fundamentally alters the ratio of runoff 's erosive energy to the ability of the ground …