Tells the story of how humans have used their ingenuity to maintain soil fertility despite continuous use, & to avoid famine through productive ag. Shows how the dev t. of towns & fixed settlements meant that methods had to be found to maintain the fertility of fields exploited year after year. The way this was done is described for the ancient Chinese, the Incas, the Maya, & the Romans. Examines the dev t. of ag. in England, particularly the use of crop rotations. Details the 17th-cent. dev t. of chemistry, & the estab. of ag. science by Davy & von Liebig. Deals with the birth of the nitrogen fixation ind y. Discusses the value of ind. nitrate to help feed the world pop n. & the environ. consequences of nitrate use in terms of pollution in waters & human health. Illus.