Ode to Soil

Abstract

A PREAMBLE: THE MEANINGS OF SOIL “Paradox” is truth spelt with seven letters instead of five. Water is a paradox (Buchan 1996). So also is soil—no other word attracts such opposites of meaning. At one extreme, its meanings include “filth,” “dirty or refuse matter,” and “excrement!” The verb “to soil” means “to bring disgrace or discredit upon.” At the other extreme, it is reverently described as “The place of one's nativity” (Shorter Oxford Dictionary 1970). Indeed, our material nativity lies at the soil–root interface (figure 1): here begins the flow of minerals into plants and then on into animals. The human body contains about 70% water and 7% minerals, derived mainly from soil (table 1). In agriculture and ecology, soil means the top 1 to 2 m (3 to 6 ft) of life-bearing material. To engineers, it is mainly inert (lifeless) material under structures; and to geologists, it includes deep sediments. Here soil is widely interpreted as earth surface materials: it is any particulate material containing sand, silt, or clay particles (figure 2), and with or without organic matter. Soil is the “fines” (i.e., particles <2 mm (0.079 in) in size) produced by the fragmentation and weathering…