G. Jock Churchman & Edward R. Landa 
Soil Underfoot [PDF ebook] 
Infinite Possibilities for a Finite Resource

The largest part of the world’s food comes from its soils, either directly from plants, or via animals fed on pastures and crops. Thus, it is necessary to maintain, and if possible, improve the quality-and hence good health-of soils, while enabling them to support the growing world population. The Soil Underfoot: Infinite Possibilities for a Finite