“You are earth, you feed on earth,
and you’ll return to earth”
Giacomo Certini
Dipartimento di Scienza del Suolo e Nutrizione della Pianta, Università di Firenze, Piazzale delle Cascine 28, 50144 Firenze, Italy
Riccardo Scalenghe
Dipartimento di Agronomia, Università di Palermo, Viale delle Scienze 13, 90128 Palermo, Italy
The importance of soil to humankind as producer, carrier, filter, and buffer is currently underlined (Various Authors 2004; Bouma 2006). We feel, however, that soil deserves wider consideration also by virtue of other less obvious functions that fulfill ancestral sanitary, psychological, and social humans’ needs. “Terra es, et de terra vivis, et in terram reverteris” (“You are earth, you feed on earth, and you’ll return to earth”) stated Saint Bernard of Clairvaux (1091-1153) in his work Meditationes piissimae de cognitione humanae conditionis. As a matter of fact, our relationship with soil lasts from birth to death, often unconscoiusly.
The first contact with soil can be the regular and intentional consumption of it, geophagy, which is still practiced by pregnant women and children worldwide (Wilson 2003). “Edible” earth may supplement poor-diets (Hooda et al. 2004) and is purchased in markets or taken from termite mounds, hut walls, and riverbeds. Adding earthy material to toxic or bitter foods to enable their consumption is a widespread practice (Johns and Duquette 1991). Carbonates have an obvious antacid effect, while some types of clay are even efficient at removing radionuclides from gastric juices (Barth and Bruckner 1969). Furthermore, it must be emphasized that much of the microflora of the gut that builds up resistance to diseases is derived originally from soil. Just from the soil Selman A. Waksman isolated the streptomycin, the first antibiotic active against tuberculosis (Waksman and Woodruff 1941). In recognition for his discovery, Dr Waksman was awarded the Nobel Prize in Medicine in 1952. However, realistically there is a great deal of literature reporting negative effects of geophagy, such as anaemia (Stokes 2006), chronic poisoning by heavy metals (Sheppard 1998), intestinal occlusion (Yé et al. 2004), perforation of the colon (Woywodt and Kiss 1999), and infections with intestinal helminthes (Luoba et al. 2005).
If the internal protective role of soil toward humans is debatable, undeniable is the external role, from both a factual and psychological point of view. Throughout history, most societies have used masks composed of earth materials to disguise or protect the face in battle, theatrical performances, or parties. Nowadays, clay facemasks are used for therapeutic or aesthetic reasons, since they stimulate the circulation of the blood and lymph systems, remove dead skin cells, absorb surface fats, tone and strengthen the connective tissues (Carretero 2002; Poensin et al. 2003). More importantly, soil products are used for protection for humans in the guise of houses. An estimated 1.5 billion people live in houses constructed of unfired earth (Keefe 2005). Plinthite (Gr. plinthos, brick) is a iron-rich and humus-poor soil horizon that simply requires to be cut into blocks and left to air-dry to form hard bricks. Soil houses are virtually fireproof and can withstand moderate earthquake shocks thanks to their ductility. Furthermore, the exhalation rate of dangerous radon (Wakefield and Kohler 1991; Law et al. 2000) from adobes is much less than that from concrete or other building materials (Minke 2006). Remarkable are the advantages of using such adobes in terms of energy saving, taking into account that the embedded energy required to produce one cubic metre of building material amounts to 10 kWh m-3 for sun-dried soil, 590 kWh m-3 for perforated fired bricks, 800 kWh m-3 for concrete blocks, 2640 kWh m-3 for ordinary Portland concrete (Keefe 2005). As a consequence, soil buildings are in increasing demand in many countries (Minke 2006). Soil contributes to saving energy also when placed untreated over the roofs and turfed, providing efficient thermal insulation (Takakura et al. 2000).
Soil can also fulfil non-primary needs of humans, such as that of expressing creativity. Nazca Lines are hundreds of gigantic individual figures, ranging in complexity from simple lines to stylized human and animal figures drawn on the Nazca Desert, Peru, between 200 BC and 700 AD. These features, the longest of which is nearly 270 m, were made by removing the iron oxide coated pebbles that cover the surface of the desert and that contrast with the light-colored earth underneath. Much more recent is Marree Man, the largest manmade artwork in the world. This geoglyph depicts a 4.2-km high man holding a boomerang and was made in Australia by anonymous creators using a 2.5-m wide, eight-tine plough attached to a tractor. The use of soil in art has not been surpassed by the development of more sophisticated materials. In contrast, it has experienced a revaluation thanks to contemporary art (Fig. 1). Jean Dubuffet coined the term “art brut” to indicate an art free from intellectual implications, appearing primitive and child-like. Dubuffet himself, Burri, Donati, Fautrier, Mathieu, Soulages, and Tàpies used bulk soil, single size fractions of soil, or tar in their artworks. “Earth art” is a form of art come to prominence in the late 1960s, with personalities such as Heizer, Long, Oppenheim, and Smithson. Earth art uses items from the natural environment, such as soil and rocks, and “earthworks” are prepared in the open air and left weathering there.
After affecting several aspects of life, our final contact with soil in most cases is burial. Soil plays a crucial role in preventing spread of germs from corpse decomposition and, thus, risk of infections for living beings. The decay of our remains within soil implies formation of a discrete, ephemeral ‘hot spot’ of biological activity directed towards the slow release of elements to the wider ecosystem (Carter et al. 2007). Part of “our” carbon is transformed into adipocere, a mix of waxy grave substances that reside in soil for several centuries (Berstan et al. 2004) and that could be viewed as our last, small, personal contribution to counteract global climate change, the present-age bogeyman.
Fig. 1 In 1998, soil rose to the dignity of the masterpiece per se thanks to Maurizio Cattelan: 8x5x5-m soil cube sustaining an olive tree at permanent collection of Castello di Rivoli, Turin, Italy (photo courtesy of Museo d'Arte Contemporanea)
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